Category: Uncategorized

The American alligator (Alligator mississippiensis), sometimes referred to as a gator, or common alligator is a large crocodilian reptile native to the Southeastern United States and a small section of northeastern Mexico. It is one of the two extant species in the genus Alligator, and is larger than the only other living alligator species, the Chinese alligator.

Adult male American alligators measure 3.4 to 4.6 m (11.2 to 15.1 ft) in length, and can weigh up to 500 kg (1,100 lb), with unverified sizes of up to 5.84 m (19.2 ft) and weights of 1,000 kg (2,200 lb) making it the second largest member by length and the heaviest of the family Alligatoridae, after the black caiman. Females are smaller, measuring 2.6 to 3 m (8.5 to 9.8 ft) in length.^{[5][6][7][8][9]} The American alligator inhabits subtropical and tropical freshwater wetlands, such as marshes and cypress swamps, from southern Texas to North Carolina.^[10] It is distinguished from the sympatric American crocodile by its broader snout, with overlapping jaws and darker coloration, and is less tolerant of saltwater but more tolerant of cooler climates than the American crocodile, which is found only in tropical and warm subtropical climates.

American alligators are apex predators and consume fish, amphibians, reptiles, birds, and mammals. Hatchlings feed mostly on invertebrates. They play an important role as ecosystem engineers in wetland ecosystems through the creation of alligator holes, which provide both wet and dry habitats for other organisms. Throughout the year (in particular during the breeding season), American alligators bellow to declare territory, and locate suitable mates.^[11] Male American alligators use infrasound to attract females. Eggs are laid in a nest of vegetation, sticks, leaves, and mud in a sheltered spot in or near the water. Young are born with yellow bands around their bodies and are protected by their mother for up to one year.^[12] This species displays parental care, which is rare for most reptiles. Mothers protect their eggs during the incubation period, and move the hatchlings to the water using their mouths.^[13]

The conservation status of the American alligator is listed as Least Concern by the International Union for Conservation of Nature. Historically, hunting had decimated their population, and the American alligator was listed as an endangered species by the Endangered Species Act of 1973. Subsequent conservation efforts have allowed their numbers to increase and the species was removed from endangered status in 1987. The species is the official state reptile of three states: Florida, Louisiana, and Mississippi.

History and taxonomy

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The American alligator was first classified in 1801 by French zoologist François Marie Daudin as Crocodilus mississipiensis. In 1807, Georges Cuvier created the genus Alligator for it,^[14] based on the English common name alligator (derived from Spanish word el lagarto, “the lizard”).

The American alligator and its closest living relative, the Chinese alligator, belong the subfamily Alligatorinae. Alligatorinae is the sister group to the caimans of Caimaninae, which together comprise the family Alligatoridae, which can be shown in the cladogram below:^[15][16]

Alligatoridae	CaimaninaeAlligatorinaeCeratosuchus burdoshi†Hassiacosuchus haupti†Navajosuchus mooki†Wannaganosuchus brachymanus†Arambourgia gaudryi†Allognathosuchus polyodon†Allognathosuchus wartheni†Procaimanoidea kayi†AlligatorAlligator prenasalis†Alligator mcgrewi†Alligator olseni†Alligator sinensis Chinese alligatorAlligator thomsoni†Alligator mefferdi†Alligator mississippiensis American alligator

Evolution

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Fossils identical to the existing American alligator are found throughout the Pleistocene, from 2.5 million to 11.7 thousand years ago.^[17] In 2016, a Late Miocene fossil skull of an alligator, dating to approximately seven or eight million years ago, was discovered in Marion County, Florida. Unlike the other extinct alligator species of the same genus, the fossil skull was virtually indistinguishable from that of the modern American alligator. This alligator and the American alligator are now considered to be sister taxa, suggesting that the A. mississippiensis lineage has existed in North America for seven to eight million years.^[1]

The alligator’s full mitochondrial genome was sequenced in the 1990s, and it suggests the animal evolved at a rate similar to mammals and greater than birds and most cold-blooded vertebrates.^[18] However, the full genome, published in 2014, suggests that the alligator evolved much more slowly than mammals and birds.^[19]

Characteristics

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Domestic American alligators range from long and slender to short and robust, possibly in response to variations in factors such as growth rate, diet, and climate.

Size

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The American alligator is a relatively large species of crocodilian. On average, it is the largest species in the family Alligatoridae, with only the black caiman being possibly larger.^[20] Weight varies considerably depending on length, age, health, season, and available food sources. Similar to many other reptiles that range expansively into temperate zones, American alligators from the northern end of their range, such as southern Arkansas, Alabama, and northern North Carolina, tend to reach smaller sizes. Large adult American alligators tend to be relatively robust and bulky compared to other similar-length crocodilians; for example, captive males measuring 3 to 4 m (9 ft 10 in to 13 ft 1 in) were found to weigh 200 to 350 kg (440 to 770 lb), although captive specimens may outweigh wild specimens due to lack of hunting behavior and other stressors.^[21][22]

Large male American alligators reach an expected maximum size up to 4.6 m (15 ft 1 in) in length and weigh up to 500 kg (1,100 lb), while females reach an expected maximum of 3 m (9 ft 10 in).^[5][6][23] However, the largest free-ranging female had a total length of 3.22 m (10 ft 7 in) and weighed 170 kg (370 lb).^[24] On rare occasions, a large, old male may grow to an even greater length.^[25][26]

Largest

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During the 19th and 20th centuries, larger males reaching 5 to 6 m (16 ft 5 in to 19 ft 8 in) were reported.^[27] The largest reported individual size was a male killed in 1890 by Edward McIlhenny^[28] on Marsh Island, Louisiana, and reportedly measured at 5.84 m (19 ft 2 in) in length, but no voucher specimen was available, since the American alligator was left on a muddy bank after having been measured due to having been too massive to relocate.^[26] If the size of this animal was correct, it would have weighed about 1,000 kg (2,200 lb).^[29] In Arkansas, a man killed an American alligator that was 4.04 m (13 ft 3 in) and 626 kg (1,380 lb).^[30] The largest American alligator ever killed in Florida was 5.31 m (17 ft 5 in), as reported by the Everglades National Park, although this record is unverified.^[31][32] The largest American alligator scientifically verified in Florida for the period from 1977 to 1993 was reportedly 4.23 m (13 ft 11 in) and weighed 473 kg (1,043 lb), although another specimen (size estimated from skull) may have measured 4.54 m (14 ft 11 in).^[21] A specimen that was 4.5 m (14 ft 9 in) long and weighed 458.8 kg (1,011.5 lb) is the largest American alligator killed in Alabama and has been declared the SCI world record in 2014.^[33][34]

Reported sizes

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showDate	Location	Reported Length	Reported Weight	Reported Girth	Reported Skull Length	Scientifically Analyzed Length	Comments

Average

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American alligators do not normally reach such extreme sizes. In mature males, most specimens grow up to about 3.4 m (11 ft 2 in) in length, and weigh up to 360 kg (790 lb),^[7] while in females, the mature size is normally around 2.6 m (8 ft 6 in), with a body weight up to 91 kg (201 lb).^[8][9] In Newnans Lake, Florida, adult males averaged 73.2 kg (161 lb) in weight and 2.47 m (8 ft 1 in) in length, while adult females averaged 55.1 kg (121 lb) and measured 2.22 m (7 ft 3 in).^[50] In Lake Griffin State Park, Florida, adults weighed on average 57.9 kg (128 lb).^[51] Weight at sexual maturity per one study was stated as averaging 30 kg (66 lb) while adult weight was claimed as 160 kg (350 lb).^[52]

Relation to age

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There is a common belief stated throughout reptilian literature that crocodilians, including the American alligator, exhibit indeterminate growth, meaning the animal continues to grow for the duration of its life. However, these claims are largely based on assumptions and observations of juvenile and young adult crocodilians, and recent studies are beginning to contradict this claim. For example, one long-term mark-recapture study (1979–2015) done at the Tom Yawkey Wildlife Center in South Carolina found evidence to support patterns of determinate growth, with growth ceasing upon reaching a certain age (43 years for males and 31 years for females).^[53]

Sexual dimorphism

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While noticeable in very mature specimens, the sexual dimorphism in size of the American alligator is relatively modest among crocodilians.^[54] For contrast, the sexual dimorphism of saltwater crocodiles is much more extreme, with mature males nearly twice as long as and at least four times as heavy as female saltwater crocodiles.^[55] Given that female American alligators have relatively higher survival rates at an early age and a large percentage of given populations consists of immature or young breeding American alligators, relatively few large mature males of the expected mature length of 3.4 m (11 ft 2 in) or more are typically seen.^[56]

Color

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Dorsally, adult American alligators may be olive, brown, gray, or black. However, they are on average one of the most darkly colored modern crocodilians (although other alligatorid family members are also fairly dark), and can reliably be distinguished by color via their more blackish dorsal scales against crocodiles.^[25] Meanwhile, their undersides are cream-colored.^[57] Some American alligators are missing or have an inhibited gene for melanin, which makes them albino. These American alligators are extremely rare and almost impossible to find in the wild. They could only survive in captivity, as they are very vulnerable to the sun and predators.^[58]

Jaws, teeth, and snout

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American alligators have 74–80 teeth.^[27] As they grow and develop, the morphology of their teeth and jaws change significantly.^[59] Juveniles have small, needle-like teeth that become much more robust and narrow snouts that become broader as the individuals develop.^[59] These morphological changes correspond to shifts in the American alligators’ diets, from smaller prey items such as fish and insects to larger prey items such as turtles, birds, and other large vertebrates.^[59] American alligators have broad snouts, especially in captive individuals. When the jaws are closed, the edges of the upper jaws cover the lower teeth, which fit into the jaws’ hollows. Like the spectacled caiman, this species has a bony nasal ridge, though it is less prominent.^[27] American alligators are often mistaken for a similar animal: the American crocodile. An easy characteristic to distinguish the two is the fourth tooth. Whenever an American alligator’s mouth is closed, the fourth tooth is no longer visible. It is enclosed in a pocket in the upper jaw. Alligators also frequently lose and replace their teeth, about once every year. ^[60] As alligators live a lengthy life, they can go through over 2,000 teeth in their lifetimes.^[61]

Bite

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Adult American alligators held the record as having the strongest laboratory-measured bite of any living animal, measured at up to 13,172 N (1,343.2 kgf; 2,961 lbf). This experiment had not been, at the time of the paper published, replicated in any other crocodilians, and the same laboratory was able to measure a greater bite force of 16,414 N (1,673.8 kgf; 3,690 lbf) in saltwater crocodiles;^[62][63] notwithstanding this very high biting force, the muscles opening the American alligator’s jaw are quite weak, and the jaws can be held closed by hand or tape when an American alligator is captured. No significant difference is noted between the bite forces of male and female American alligators of equal size.^[59] Another study noted that as the American alligator increases in size, the force of its bite also increases.^[64]

Movement

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X-ray video of a female American alligator showing contraction of the lungs while breathing

When on land, an American alligator moves either by sprawling or walking, the latter involving the reptile lifting its belly off the ground. The sprawling of American alligators and other crocodylians is not similar to that of salamanders and lizards, being similar to walking. Therefore, the two forms of land locomotion can be termed the “low walk” and the “high walk”. Unlike most other land vertebrates, American alligators increase their speed through the distal rather than proximal ends of their limbs.^[65]

In the water, American alligators swim like fish, moving their pelvic regions and tails from side to side.^[66] Swimming is assisted by webbed rear feet as well, which bear four toes in contrast to the five toes of the front feet.^[67][68] During respiration, air flow is unidirectional, looping through the lungs during inhalation and exhalation;^[69] the American alligator’s abdominal muscles can alter the position of the lungs within the torso, thus shifting the center of buoyancy, which allows the American alligator to dive, rise, and roll within the water.^[70]

Distribution

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American alligators, being native both to the Nearctic and Neotropical realms, are found in the wild in the Southeastern United States, from the Lowcountry in South Carolina, south to Everglades National Park in Florida, and west to the southeastern region of Texas.^[71] They are found in parts of North Carolina, South Carolina, Georgia, Florida, Louisiana, Alabama, Mississippi, Arkansas, Oklahoma and Texas. Some of these locations appear to be relatively recent introductions, with often small but reproductive populations.^[72] Louisiana has the largest American alligator population of any U.S. state. In the future, possible American alligator populations may be found in areas of Mexico adjacent to the Texas border.^[73] The range of the American alligator is slowly expanding northwards, including into areas they once found such as Virginia.^[74] American alligators have been naturally expanding their range into Tennessee,^[75] and have established a small population in the southwestern part of that state via inland waterways, according to the state’s wildlife agency.^[76] They have been extirpated from Virginia, and occasional vagrants from North Carolina wander into the Great Dismal Swamp.^[77]

In 2021, an individual was found in Calvert County, Maryland, near Chesapeake Bay, where it was shot and killed by a hunter using a crossbow. Additional reports of American alligators from this region exist, though they are believed to be escaped or released exotic pets.^[78]

Conservation status

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American alligators are currently listed as least concern by the IUCN Red List,^[2] even though from the 1800s to the mid-1900s, they were being hunted and poached by humans unsustainably.

Historically, hunting and habitat loss have severely affected American alligator populations throughout their range, and whether the species would survive was in doubt. In 1967, the American alligator was listed as an endangered species (under a law that was the precursor to the Endangered Species Act of 1973), since it was believed to be in danger of extinction throughout all or a significant portion of its range.^[79]

Both the United States Fish and Wildlife Service (USFWS) and state wildlife agencies in the South contributed to the American alligator’s recovery. Protection under the Endangered Species Act allowed the species to recuperate in many areas where it had been depleted. States began monitoring their American alligator populations to ensure that they would continue to grow. In 1987, the USFWS removed the animal from the endangered species list, as it was considered to be fully recovered.^[80] The USFWS still regulates the legal trade in American alligators and their products to protect still endangered crocodilians that may be passed off as American alligators during trafficking.^[79]

American alligators are listed under Appendix II of the Convention on International Trade in Endangered Species (CITES) meaning that international trade in the species (including parts and derivatives) is regulated.^[3]

Habitat

[edit]American alligator in the Everglades

They inhabit swamps, streams, rivers, ponds, and lakes as well as wetland prairies interspersed with shallow open water and canals with associated levees.^[81] A lone American alligator was spotted for over 10 years living in a river north of Atlanta, Georgia.^[82] Females and juveniles are also found in Carolina Bays and other seasonal wetlands. While they prefer fresh water, American alligators may sometimes wander into brackish water,^[83] but are less tolerant of salt water than American crocodiles, as the salt glands on their tongues do not function.^[84] One study of American alligators in north-central Florida found the males preferred open lake water during the spring, while females used both swampy and open-water areas. During summer, males still preferred open water, while females remained in the swamps to construct their nests and lay their eggs. Both sexes may den underneath banks or clumps of trees during the winter.^[50]

In some areas of their range, American alligators are an unusual example of urban wildlife; golf courses are often favored by the species due to an abundance of water and a frequent supply of prey animals such as fish and birds.^[85][86]

Cold tolerance

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American alligators are less vulnerable to cold than American crocodiles. Unlike an American crocodile, which would immediately succumb to the cold and drown in water at 45 °F (7 °C) or less, an American alligator can survive in such temperatures for some time without displaying any signs of discomfort.^[87] This adaptiveness is thought to be why American alligators are widespread further north than the American crocodile.^[87] In fact, the American alligator is found farther from the equator and is more equipped to handle cooler conditions than any other crocodilian.^[88] When the water begins to freeze, American alligators go into a period of brumation; they stick their snouts through the surface, which allows them to breathe above the ice,^[83] and they can remain in this state for several days.^[89]

Ecology and behavior

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Basking

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American alligators primarily bask on shore, but also climb into and perch on tree limbs to bask if no shoreline is available. This is not often seen, since if disturbed, they quickly retreat back into the water by jumping from their perch.^[90]

Holes

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American alligators modify wetland habitats, most dramatically in flat areas such as the Everglades, by constructing small ponds known as alligator holes. This behavior has qualified the American alligator to be considered a keystone species. Alligator holes retain water during the dry season and provide a refuge for aquatic organisms, which survive the dry season by seeking refuge in alligator holes, so are a source of future populations. The construction of nests along the periphery of alligator holes, as well as a buildup of soils during the excavation process, provides drier areas for other reptiles to nest and a place for plants that are intolerant of inundation to colonize. Alligator holes are an oasis during the Everglades dry season, so are consequently important foraging sites for other organisms.^[91] In the limestone depressions of cypress swamps, alligator holes tend to be large and deep, while those in marl prairies and rocky glades are usually small and shallow, and those in peat depressions of ridge and slough wetlands are more variable.^[92]

Feeding

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• Baby eating a southern leopard frog
• Young alligator eating a bullfrog
• Young alligator eating worms
• Eating a Florida gar
• Eating a pleco
• Eating a swimmer crab
• Eating a redhead duck
• Eating a great blue heron
• Eating a Florida softshell turtle
• Eating a cooter
• Eating a nutria
• Eating a feral pig
• Killing an invasive Burmese python, which is attempting to coil around it
• With deer

Bite and mastication

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The teeth of the American alligator are designed to grip prey, but cannot rip or chew flesh like teeth of some other predators (such as canids and felids), and depend on their gizzard, instead, to masticate their food. The attainment of adulthood enables the consumption of large mammals and the crushing of large turtles.^[93] The American alligator is capable of biting through a turtle’s shell or a moderately sized mammal bone.^[94]

Possible tool use

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American alligators have been documented using lures to hunt prey such as birds.^[95] This means they are among the first reptiles recorded to use tools. By balancing sticks and branches on their heads, American alligators are able to lure birds looking for suitable nesting material to kill and consume. This strategy, which is shared by the mugger crocodile, is particularly effective during the nesting season, in which birds are more likely to gather appropriate nesting materials.^[96] This strategy has been documented in two Florida zoos occurring multiple times a day in peak nesting season and in some parks in Louisiana. The use of tools was documented primarily during the peak rookery season when birds were primarily looking for sticks.^[97]

However, a three-day experiment to reproduce the use of sticks as lures, published in 2019, failed to document the behavior. Researchers placed sticks at densities of 30 to 35 sticks per meter squared near four captive populations, two near rookeries and two at no-rookery sites. While stick-displaying behavior was observed several times, it was not more frequent near rookeries. In fact, in some comparisons, it was associated with no-rookery sites. This implies American alligators do not tailor this behavior to specific contexts, leaving the purpose, if any, of stick-displaying ambiguous.^[98]

Aquatic vs terrestrial prey

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Fish and other aquatic prey taken in the water or at the water’s edge form the major part of American alligator’s diet and may be eaten at any time of the day or night. Adult American alligators also spend considerable time hunting on land, up to 160 feet (50 m) from water, ambushing terrestrial animals on trailsides and road shoulders. Usually, terrestrial hunting occurs on nights with warm temperatures.^[99] When hunting terrestrial prey, American alligators may also ambush them from the edge of the water by grabbing them and pulling the prey into the water, the preferred method of predation of larger crocodiles.^[25]

Additionally, American alligators have recently been filmed and documented killing and eating sharks and rays; four incidents documented indicated that bonnetheads, lemon sharks, Atlantic stingrays, and nurse sharks are components of the animal’s diet. Sharks are also known to prey on American alligators, in turn, indicating that encounters between the two predators are common.^[100][101]

Common prey

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American alligators are considered an apex predator throughout their range. They are opportunists and their diet is determined largely by both their size and age and the size and availability of prey. Most American alligators eat a wide variety of animals, including invertebrates, fish, birds, turtles, snakes, amphibians, and mammals. Hatchlings mostly feed on invertebrates such as insects, insect larvae, snails, spiders, and worms, as well as small fish and frogs.^[102][103] As they grow, American alligators gradually expand to larger prey. Once an American alligator reaches full size and power in adulthood, any animal living in the water or coming to the water to drink is potential prey. Most animals captured by American alligators are considerably smaller than itself.^[27] A few examples of animals consumed are largemouth bass, spotted gar, freshwater pearl mussels, American green tree frogs, yellow mud turtles, cottonmouths, common moorhens, and feral wild boars.^[102] Stomach contents show, among native mammals, muskrats and raccoons are some of the most commonly eaten species.^[104] In Louisiana, where introduced nutria are common, they are perhaps the most regular prey for adult American alligators, although only larger adults commonly eat this species.^[105][104] It has also been reported that large American alligators prey on medium-sized American alligators, which had preyed on hatchlings and smaller juveniles.^[106]

If an American alligator’s primary food resource is not available, it will sometimes feed on carrion and non-prey items such as rocks and artificial objects, like bottle caps. These items help the American alligator in the process of digestion by crushing up the meat and bones of animals, especially animals with shells.^[102]

Large animals

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Other animals may occasionally be eaten, even large deer or feral wild boars, but these are not normally part of the diet. American alligators occasionally prey on large mammals, but usually do so when fish and smaller prey levels go down.^[107] Rarely, American alligators have been observed killing and eating bobcats, but such events are not common and have little effect on bobcat populations.^[108][109] Although American alligators have been listed as predators of the Nilgai and the West Indian manatees, very little evidence exists of such predation.^[110] In the 2000s, when invasive Burmese pythons first occupied the Everglades, American alligators have been recorded preying on sizable snakes, possibly controlling populations and preventing the invasive species from spreading northwards.^[111] However, the python is also known to occasionally prey on alligators, a form of both competition and predation.^[112] American alligator predation on Florida panthers is rare, but has been documented. Such incidents usually involve a panther trying to cross a waterway or coming down to a swamp or river to get a drink.^[113] American alligator predation on American black bears has also been recorded.^{[114][115][116]}

Domestic animals

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Occasionally, domestic animals, including dogs, cats, and calves, are taken as available, but are secondary to wild and feral prey.^[27] Other prey, including snakes, lizards, and various invertebrates, are eaten occasionally by adults.^[25]

Birds

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Water birds, such as herons, egrets, storks, waterfowl and large dabbling rails such as gallinules or coots, are taken when possible. Occasionally, unwary adult birds are grabbed and eaten by American alligators, but most predation on bird species occurs with unsteady fledgling birds in late summer, as fledgling birds attempt to make their first flights near the water’s edge.^[25]

Fruit

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In 2013, American alligators and other crocodilians were reported to also eat fruit.^[117] Such behavior has been witnessed, as well as documented from stomach contents, with the American alligators eating such fruit as wild grapes, elderberries, and citrus fruits directly from the trees. Thirty-four families and 46 genera of plants were represented among seeds and fruits found in the stomach contents of American alligators.^[118] The discovery of this unexpected part of the American alligator diet further reveals that they may be responsible for spreading seeds from the fruit they consume across their habitat.^[119]

Cooperative hunting

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Additionally, American alligators engage in what seems to be cooperative hunting.^[120][121] One observation of cooperative hunting techniques was where there are pushing American alligators and catching American alligators and they were observed taking turns in each position. Another observation said that about 60 American alligators gathered in an area and would form a semicircle with about half of them and would push the fish closer to the bank. Once one of the American alligators caught a fish another one would enter into its spot, and it would take the fish to the resting area. This was reported to have occurred two days in a row.^[122]

In Florida and East Texas

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The diet of adult American alligators from central Florida lakes is dominated by fish, but the species is highly opportunistic based upon local availability. In Lake Griffin, fish made up 54% of the diet by weight, with catfish being most commonly consumed, while in Lake Apopka, fish made up 90% of the food and mostly shad were taken; in Lake Woodruff, the diet was 84% fish and largely consists of bass and sunfish. Unusually in these regions, reptiles and amphibians were the most important nonpiscivore prey, mostly turtles and water snakes.^[123] In southern Louisiana, crustaceans (largely crawfish and crabs) were found to be present in the southeastern American alligators, but largely absent in southwestern American alligators, which consumed a relatively high proportion of reptiles, although fish were the most recorded prey for adults, and adult males consumed a large portion of mammals.^[124]

In East Texas, diets were diverse and adult American alligators took mammals, reptiles, amphibians, and invertebrates (e.g. snails) in often equal measure as they did fish.^[125]

Vocalizations

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Alligator bellow

Duration: 24 seconds.0:24

Alligator bellow, ogg/Vorbis format

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Another alligator bellow

Duration: 22 seconds.0:22

Alligator bellow, ogg/Vorbis format

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Alligator hiss

Duration: 12 seconds.0:12

Alligator hiss ogg/Vorbis format

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Problems playing these files? See media help.

Mechanism

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An American alligator is able to abduct and adduct the vocal folds of its larynx, but not to elongate or shorten them; yet in spite of this, it can modulate fundamental frequency very well.^[126] Their vocal folds consists of epithelium, lamina propria and muscle. Sounds ranged from 50 to 1200 Hz. In one experiment conducted on the larynx, the fundamental frequency depended on both the glottal gap and stiffness of the larynx tissues. As the frequency increases, there’s high tension and large strains. The fundamental frequency has been influenced by the glottal gap size and subglottal pressure and when the phonation threshold pressure has been exceeded, there will be vocal fold vibration.^[127]

Calls

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Crocodilians are the most vocal of all non-avian reptiles and have a variety of different calls depending on the age, size, and sex of the animal.^[128] The American alligator can perform specific vocalizations to declare territory, signal distress, threaten competitors, and locate suitable mates. Juveniles can perform a high-pitched hatchling call (a “yelping” trait common to many crocodilian species’ hatchling young)^[129] to alert their mothers when they are ready to emerge from the nest. Juveniles also make a distress call to alert their mothers if they are being threatened. Adult American alligators can growl, hiss, or cough to threaten others and declare territory.

Bellowing

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Both males and females bellow loudly by sucking air into their lungs and blowing it out in intermittent, deep-toned roars to attract mates and declare territory.^[130] Males are known to use infrasound during mating bellows. Their bellowing initiates the beginning of the courtship period for American alligators.^[131] Bellowing is performed in a “head oblique, tail arched” posture. Infrasonic waves from a bellowing male can cause the surface of the water directly over and to either side of his back to literally “sprinkle”,^[132] in what is commonly called the “water dance”.^[133] Large bellowing “choruses” of American alligators during the breeding season are commonly initiated by females and perpetuated by males.^[134] Observers of large bellowing choruses have noted they are often felt more than they are heard due to the intense infrasound emitted by males. American alligators bellow in B flat (specifically “B♭₁“, defined as an audio frequency of 58.27 Hz), and bellowing choruses can be induced by tuba players, sonic booms, and large aircraft.^[135]

Lifespan

[edit]

American alligators typically live to the age of 50, and possibly over 70 years old. Males reach sexual maturity at around 11.6 years, and females at around 15.8 years. Although it was originally thought that American alligators never stop growing, studies have now found that males stop growing at around the age of 43 years, and females stop growing at around the age of 31 years.^[53]

Reproduction

[edit]

Breeding season

[edit]

The breeding season begins in the spring. On spring nights, American alligators gather in large numbers for group courtship, in the aforementioned “water dances”.^[136] A study conducted in the 1980s at an alligator farm showed that homosexual courtship is common, with two-thirds of the recorded instances of sexual behaviour having been between two males.^[137] The female builds a nest of vegetation, sticks, leaves, and mud in a sheltered spot in or near the water.

Eggs

[edit]

After the female lays her 20 to 50 white eggs, about the size of a goose egg, she covers them with more vegetation, which heats as it decays, helping to keep the eggs warm. This differs from Nile crocodiles, which lay their eggs in pits.^[87] The temperature at which American alligator eggs develop determines their sex (see temperature-dependent sex determination). Studies have found that eggs hatched at a temperature below 88.7 °F (31.5 °C) or a temperature above 94.1 °F (34.5 °C) will produce female offspring, while those at a temperature between 90.5 and 92.3 °F (32.5 and 33.5 °C) will produce male offspring.^[138] The nests built on levees are warmer, thus produce males, while the cooler nests of wet marsh produce females.^[139] The female remains near the nest throughout the 65-day incubation period, protecting it from intruders. When the young begin to hatch — their “yelping” calls can sometimes even be heard just before hatching commences — the mother quickly digs them out and carries them to the water in her mouth,^[27] as some other crocodilian species are known to do.

Young

[edit]

The young are tiny replicas of adults, with a series of yellow bands around their bodies that serve as camouflage.^[27] Hatchlings gather into pods and are guarded by their mother and keep in contact with her through their “yelping” vocalizations. Young American alligators eat small fish, frogs, crayfish, and insects.^[140] They are preyed on by large fish, birds, raccoons, Florida panthers, and adult American alligators.^[27] Mother American alligators eventually become more aggressive towards their young, which encourages them to disperse.^[140] Young American alligators grow 3–8 in (7.6–20.3 cm) a year and reach adulthood at 6 ft (1.8 m).^[83]

Parasites

[edit]

American alligators are commonly infected with parasites. In a 2016 Texas study, 100% of the specimens collected were infected with parasites, and by at least 20 different species of parasites, including lung pentastomids, gastric nematodes, intestinal helminths. When compared to American alligators from different states there was no significant difference in prevalence.^[141]

Interactions with exotic species

[edit]

Nutria were introduced into coastal marshes from South America in the mid-20th century, and their population has since exploded into the millions. They cause serious damage to coastal marshes and may dig burrows in levees. Hence, Louisiana has had a bounty to try to reduce nutria numbers. Large American alligators feed heavily on nutria, so American alligators may not only control nutria populations in Louisiana, but also prevent them spreading east into the Everglades. Since hunting and trapping preferentially take the large American alligators that are the most important in eating nutria, some changes in harvesting may be needed to capitalize on their ability to control nutria.^[105]

Recently, a population of Burmese pythons became established in Everglades National Park. Substantial American alligator populations in the Everglades might be a contributing factor, as a competitor, in keeping the python populations low, preventing the spread of the species north. While events of predation by Burmese pythons on sizable American alligators have been observed,^{[112][142][143]} no evidence of a net negative effect has been seen on overall American alligator populations.^[144]

Indicators of environmental restoration

[edit]

American alligators play an important role in the restoration of the Everglades as biological indicators of restoration success.^[145] American alligators are highly sensitive to changes in the hydrology, salinity, and productivity of their ecosystems; all are factors that are expected to change with Everglades restoration. American alligators also may control the long-term vegetation dynamics in wetlands by reducing the population of small mammals, particularly nutria, which may otherwise overgraze marsh vegetation.^[105] In this way, the vital ecological service they provide may be important in reducing rates of coastal wetland losses in Louisiana.^[146] They may provide a protection service for water birds nesting on islands in freshwater wetlands. American alligators prevent predatory mammals from reaching island-based rookeries and in return eat spilled food and birds that fall from their nests. Wading birds appear to be attracted to areas with American alligators and have been known to nest at heavily trafficked tourist attractions with large numbers of American alligators, such as the St. Augustine Alligator Farm in St. Augustine, Florida.^[147]

Relationship with humans

[edit]

Attacks on humans

[edit]

Main article: List of fatal alligator attacks in the United States

American alligators are capable of killing humans, but fatal attacks are rare. Mistaken identity leading to an attack is always possible, especially in or near cloudy waters. American alligators are often less aggressive towards humans than larger crocodile species, a few of which (mainly the Nile and saltwater crocodiles) may prey on humans with some regularity.^[26][148] Alligator bites are serious injuries, due to the reptile’s sheer bite force and risk of infection. Even with medical treatment, an American alligator bite may still result in a fatal infection.^[149]

As human populations increase, and as they build houses in low-lying areas, or fish or hunt near water, incidents are inevitable where humans intrude on American alligators and their habitats. Since 1948, 257 documented attacks on humans in Florida (about five incidents per year) have been reported, of which an estimated 23 resulted in death.^[150] Only nine fatal attacks occurred in the United States throughout the 1970s–1990s, but American alligators killed 12 people between 2001 and 2007. An additional report of alligator attacks showed a total of 376 injuries and 15 deaths recorded all from 1948 to 2004, leading this to an increase of the alligator population.^[151] In May 2006, American alligators killed three Floridians in less than a week.^[152] At least 28 fatal attacks by American alligators have occurred in the United States since 1970.

Wrestling

[edit]

Main article: Alligator wrestling

Since the late 1880s, alligator wrestling has been a source of entertainment for some. Created by the Miccosukee and Seminole tribes prior to its popularity for tourism, this tourism tradition remains popular despite criticism from animal-rights activists.^[153]

Farming

[edit]

Main article: Alligator farm

Today, alligator farming is a large, growing industry in Georgia, Florida, Texas, and Louisiana. These states produce a combined annual total of some 45,000 alligator hides. Alligator hides bring good prices and hides in the 6- to 7-ft range have sold for $300 each.^[154] The market for alligator meat is growing, and about 300,000 pounds (140,000 kg) of meat are produced annually.^[155] According to the Florida Department of Agriculture and Consumer Services, raw alligator meat contains roughly 200 Calories (840 kJ) per 3-oz (85-g) portion, of which 27 Calories (130 kJ) come from fat.

Culture and film

[edit]

The American alligator is the official state reptile of Florida,^[156] Louisiana,^[157] and Mississippi.^[158] Several organizations and products from Florida have been named after the animal.

“Gators” has been the nickname of the University of Florida‘s sports teams since 1911. In 1908, a printer made a spur-of-the-moment decision to print an alligator emblem on a shipment of the school’s football pennants.^[159] The mascot stuck, and was made official in 1911, perhaps because the team captain’s nickname was Gator.^[160] Allegheny College and San Francisco State University both have Gators as their mascots, as well.^[161]

The Gator Bowl is a college football game held in Jacksonville annually since 1946, with Gator Bowl Stadium hosting the event until the 1993 edition. The Gatornationals is a NHRA drag race held at the Gainesville Raceway in Gainesville since 1970.

The grizzly bear (Ursus arctos horribilis), also known as the North American brown bear or simply grizzly, is a population or subspecies^[4] of the brown bear inhabiting North America.

In addition to the mainland grizzly (Ursus arctos horribilis), other morphological forms of brown bear in North America are sometimes identified as grizzly bears. These include three living populations—the Kodiak bear (U. a. middendorffi), the Kamchatka bear (U. a. beringianus), and the peninsular grizzly (U. a. gyas)—as well as the extinct California grizzly (U. a. californicus†)^[5][6] and Mexican grizzly (formerly U. a. nelsoni†).^[7][8] On average, grizzly bears near the coast tend to be larger while inland grizzlies tend to be smaller.

The Ussuri brown bear (U. a. lasiotus), inhabiting the Ussuri Krai, Sakhalin, the Amur Oblast, the Shantar Islands, Iturup Island, and Kunashir Island in Siberia, northeastern China, North Korea, and Hokkaidō in Japan,^[6][9][10] is sometimes referred to as the “black grizzly”, although it is no more closely related to North American brown bears than other subspecies of the brown bear around the world.

Classification

Meaning of “grizzly”

Meriwether Lewis and William Clark first described it as grisley, which could be interpreted as either “grizzly” (i.e., “grizzled”—that is, with grey-tipped hair) or “grisly” (“fear-inspiring”, now usually “gruesome”).^[11] The modern spelling supposes the former meaning; even so, naturalist George Ord formally classified it in 1815 as U. horribilis for its character.^[12]

Evolution and genetics

Phylogenetics

Several studies have been conducted on the genetic history of the grizzly bear.^[13][14][15] Classification has been revised along genetic lines.^[5] There are two morphological forms of Ursus arctos: the grizzly and the coastal brown bears, but these morphological forms do not have distinct mtDNA lineages.^[16] The genome of the grizzly bear was sequenced in 2018 and found to be 2,328.64Mb (mega-basepairs) in length, and contain 30,387 genes.^[17]

Ursus arctos

Brown bears originated in Eurasia, and first migrated to North America between 177,000 BP ~ 111,000 BP.^[13] Most grizzly bears belong to this initial population of North American brown bear (clade 4), which continues to be the dominant mitochondrial grouping south of subarctic North America. Genetic divergences suggest brown bears first migrated south during MIS-5 (~92,000 – 83,000 BP) upon the opening of the ice-free corridor,^[13][18] with the first fossils being near Edmonton (26,000 BP).^[19] Other mitochondrial lineages appear later- the Alexander and Haida Gwaii archipelagoes have an endemic lineage, which first appears around 20,000 BP. After a local extinction in Beringia ~33,000 BP, two closely related lineages repopulated Alaska and northern Canada from Eurasia after the Last Glacial Maximum (>25,000 BP).^[13]

In the 19th century, the grizzly was classified as 86 distinct species. By 1928 only seven grizzly species remained,^[6] and by 1953, only one species remained globally.^[20] However, modern genetic testing reveals the grizzly to be a subspecies of the brown bear (Ursus arctos). Biologist R.L. Rausch found that North America has but one species of grizzly.^[4] Therefore, everywhere it is the “brown bear”; in North America, it is the “grizzly”, but these are all the same species, Ursus arctos.

Subspecies in North America

In 1963, Rausch reduced the number of North American subspecies to one, Ursus arctos middendorffi.^[21] Further testing of Y-chromosomes is required to yield an accurate new taxonomy with different subspecies.^[5] Coastal grizzlies, often referred to by the popular but geographically redundant synonym of “brown bear” or “Alaskan brown bear” are larger and darker than inland grizzlies, which is why they, too, were considered a different species from grizzlies. Kodiak Grizzly Bears were also at one time considered distinct. Therefore, at one time the thought was there were five different “species” of brown bear, including three in North America.^[22]

It remains an open question how many subspecies of Ursus arctos are present in North America. Traditionally, the following have been recognized alongside U. a. horribilis proper: Alaskan brown bear (U. a. alascensis), California grizzly bear (U. a. californicus), Dall Island brown bear (U. a. dalli), the Alaska Peninsula brown bear (U. a. gyas), Kodiak bear (U. a. middendorffi), Mexican grizzly bear (U. a. nelsoni), ABC Islands bear (U. a. sitkensis), and Stickeen brown bear (U. a. stikeenensis).^[23]

One study based on mitochondrial DNA recovered no distinct genetic groupings of North American brown bears, implying that previous grizzly bear subspecies designations are unwarranted and these bears should all be considered populations of U. a. horribilis.^[3] The only genetically anomalous grouping was the ABC Islands bear, which bears genetic introgression from the polar bear.^[24] A formal taxonomic revision was not performed, however, and the implied synonymy has not been accepted by taxonomic authorities.^[25][26] Furthermore, a recent whole-genome study suggests that certain Alaskan brown bears, including the Kodiak and Alaskan Peninsula grizzly bears, are members of a Eurasian brown bear lineage, more closely related to the Kamchatka brown bear than to other North American brown bears.^[27] Until the systematics of North American brown bears is studied in more depth, other North American subspecies have been provisionally considered separate from U. a. horribilis.^[28]

Appearance

Size

Grizzly bears are some of the largest subspecies of brown bear, only being beaten by the Kamchatka brown bears and the Kodiak bears. Grizzly bears vary in size depending on timing and populations.

The largest populations are the coastal grizzlies in the Alaskan peninsula, with males weighing 389 kilograms (858 lb) and females weighing 207 kilograms (456 lb).^[29]

The populations in northern interior Canada are much smaller, with males weighing 139 kilograms (306 lb) and females weighing 95 kilograms (209 lb). This is actually similar to the American black bear population of the area.^[29]

Average total length in this subspecies is between 198 cm (78 in) and 240 cm (94 in),^[30] with an average shoulder height of 102 cm (40 in) and hindfoot length of 28 cm (11 in).^[31] Newborn bears may weigh less than 500 g (18 oz).

Characteristics

Although variable in color from blond to nearly black, grizzly bear fur is typically brown with darker legs and commonly white or blond tipped fur on the flank and back.^[32]

Grizzly bears overlap with Black Bears in range, but there are numerous factors that can differentiate the two:

• A pronounced muscular hump appears on adult grizzlies’ shoulders; black bears do not have this hump.
• Aside from the distinguishing hump a grizzly bear can be identified by a “dished in” profile of their face with short, rounded ears, whereas a black bear has a straight face profile and longer ears.^[33]
• A grizzly bear can also be identified by its rump, which is lower than its shoulders; a black bear’s rump is higher than its shoulders.^[33]
• A grizzly bear’s front claws measure about 51–102 mm (2–4 in) in length; a black bear’s claws measure about 25–51 mm (1–2 in) in length.^[33]

Range

In North America, grizzly bears previously ranged from Alaska down to Mexico and as far east as the western shores of Hudson Bay;^[34] the species is now found in Alaska, south through much of western Canada, and into portions of the northwestern United States (including Washington, Idaho, Montana, and Wyoming), extending as far south as Yellowstone and Grand Teton National Parks.^[35] In Canada, there are approximately 25,000 grizzly bears occupying British Columbia, Alberta, the Yukon, the Northwest Territories, Nunavut, and the northern part of Manitoba.^[34]

An article published in 1954 suggested they may be present in the tundra areas of the Ungava Peninsula and the northern tip of Labrador–Quebec.^[36] In British Columbia, grizzly bears inhabit approximately 90% of their original territory. There were approximately 25,000 grizzly bears in British Columbia when the European settlers arrived.^[34] However, population size has since significantly decreased due to hunting and habitat loss. In 2008, it was estimated there were 16,000 grizzly bears. A revised Grizzly bear count in 2012 for British Columbia was 15,075.^[37] Population estimates for British Columbia are based on hair-snagging, DNA-based inventories, mark-and-recapture, and a refined multiple regression model.^[38] In 2003, researchers from the University of Alberta spotted a grizzly on Melville Island in the high Arctic, which is the most northerly sighting ever documented.^[39][40]

Populations

Around 60,000 wild grizzly bears are located throughout North America, 30,000 of which are found in Alaska.^[34] and up to 29,000 live in Canada. The Alaskan population of 30,000 individuals is the highest population of any province / state in North America. Populations in Alaska are densest along the coast, where food supplies such as salmon are more abundant.^[41] The Admiralty Island National Monument protects the densest population: 1,600 bears on a 1,600 square-mile island.^[42] The majority of Canada’s grizzlies live in British Columbia.^[43]

In the lower 48 United States, around 1,000 are found in the Northern Continental Divide in northwestern Montana.^[44] About 1,000 more live in the Greater Yellowstone Ecosystem in the tri-state area of Wyoming, Idaho and Montana.^[45] There are an estimated 70–100 grizzly bears living in northern and eastern Idaho. In September 2007, a hunter produced evidence of one bear in the Selway-Bitterroot Wilderness ecosystem, by killing a male grizzly bear there.^[46]

In the North Cascades ecosystem of northern Washington, grizzly bear populations are estimated to be fewer than 20 bears, but there is a longterm management plan to reintroduce the bears to North Cascades National Park.^[47]

Extirpated populations and recovery

The grizzly bear’s original range included much of the Great Plains and the southwestern states, but it has been extirpated in most of those areas. Combining Canada and the United States, grizzly bears inhabit approximately half the area of their historical range.^[34]

Although the once-abundant California grizzly bear appears prominently on the state flag of California and was the symbol of the Bear Flag Republic before the state of California’s admission to the Union in 1850, the subspecies or population is currently extinct. The last known grizzlies in California were killed in the Sierra foothills east of Fresno in the early 1920s.^[48]

The killing of the last grizzly bear in Arizona in 1936 at Escudilla Mountain is included in Aldo Leopold‘s Sand County Almanac.^[49] There has been no confirmed sighting of a grizzly in Colorado since 1979.^[50]

Other provinces and the United States may use a combination of methods for population estimates. Therefore, it is difficult to say precisely what methods were used to produce total population estimates for Canada and North America, as they were likely developed from a variety of studies. The grizzly bear currently has legal protection in Mexico, European countries, some areas of Canada, and in all of the United States. However, it is expected that repopulating its former range will be a slow process, due to various reasons, including the bear’s slow reproductive habits and the effects of reintroducing such a large animal to areas prized for agriculture and livestock.

Biology

Hibernation

Grizzly bears hibernate for five to seven months each year^[51] (except where the climate is warm—the California grizzly did not hibernate).^[6] During this time, female grizzly bears give birth to their offspring, who then consume milk from their mother and gain strength for the remainder of the hibernation period.^[52] To prepare for hibernation, grizzlies must prepare a den and consume an immense amount of food because they do not eat during hibernation. Grizzly bears also do not defecate or urinate throughout the entire hibernation period. The male grizzly bear’s hibernation ends in early to mid-March, while females emerge in April or early May.^[53]

In preparation for winter, bears can gain approximately 180 kg (400 lb), during a period of hyperphagia, before going into hibernation.^[54] The bear often waits for a substantial snowstorm before it enters its den: such behavior lessens the chances that predators will find the den. The dens are typically at elevations above 1,800 meters (5,900 ft) on north-facing slopes.^[55] There is some debate among professionals as to whether grizzly bears technically hibernate: much of this debate revolves around body temperature and the ability of the bears to move around during hibernation on occasion. Grizzly bears can “partially” recycle their body wastes during this period.^[56] Although inland or Rocky Mountain grizzlies spend nearly half of their life in dens, coastal grizzlies with better access to food sources spend less time in dens. In some areas where food is very plentiful year round, grizzly bears skip hibernation altogether.^[57]

Reproduction

Except for females with cubs,^[58] grizzlies are normally solitary, active animals, but in coastal areas, grizzlies gather around streams, lakes, rivers, and ponds during the salmon spawn. Females (sows) produce one to four young (usually two) that are small and weigh only about 450 g (16 oz) at birth. A sow is protective of her offspring and will attack if she thinks she or her cubs are threatened.

Grizzly bears have one of the lowest reproductive rates of all terrestrial mammals in North America.^[59] This is due to numerous ecological factors. Grizzly bears do not reach sexual maturity until they are at least five years old.^[34][60] Once mated with a male in the summer, the female delays embryo implantation until hibernation, during which miscarriage can occur if the female does not receive the proper nutrients and caloric intake.^[61] On average, females produce two cubs in a litter^[60] and the mother cares for the cubs for up to two years, during which the mother will not mate.^[34]

Once the young leave or are killed, females may not produce another litter for three or more years, depending on environmental conditions.^[62] Male grizzly bears have large territories, up to 4,000 km² (1,500 sq mi),^[59] making finding a female scent difficult in such low population densities. Population fragmentation of grizzlies may destabilize the population from inbreeding depression. The gestation period for grizzly bears is approximately 180–250 days.

Litter size varies between one and four cubs, typically comprising twins or triplets. Cubs are always born in the mother’s winter den while she is in hibernation. Female grizzlies are fiercely protective of their cubs, being able to fend off predators including larger male bears.^[63] Cubs feed entirely on their mother’s milk until summer comes, after which they still drink milk but begin to eat solid foods. Cubs gain weight rapidly during their time with the mother—their weight will have increased from 4.5 to 45 kg (9.9 to 99.2 lb) in the two years spent with the mother. Mothers may see their cubs in later years but both avoid each other.^[64]

Lifespan

The average lifespan for a male is estimated at 22 years, with that of a female being slightly longer at 26.^[65] Females live longer than males due to their less dangerous life; they do not engage in seasonal breeding fights as males do. The oldest known wild inland grizzly was about 34 years old in Alaska; the oldest known coastal bear was 39,^[66] but most grizzlies die in their first year of life.^[67] Captive grizzlies have lived as long as 47 years.^[68]

Movement

They have a tendency to chase fleeing animals,^[69] and although it has been said anecdotally that grizzly bears (Ursus arctos horribilis) can run at 56 km/h (35 mph), the maximum speed reliably recorded at Yellowstone is 48 km/h (30 mph).^[70] In addition, they can climb trees.^[69]

Ecology

Diet

See also: HypocarnivoreWild grizzly bears at Brooks Falls, Alaska

Although grizzlies are of the order Carnivora and have the digestive system of carnivores, they are normally omnivores: their diets consist of both plants and animals. They have been known to prey on large mammals, when available, such as moose, elk, caribou, white-tailed deer, mule deer, bighorn sheep, bison, and even black bears, though they are more likely to take calves and injured individuals rather than healthy adults. Grizzly bears feed on fish such as salmon, trout, and bass, and those with access to a more protein-enriched diet in coastal areas potentially grow larger than inland individuals. Grizzly bears also readily scavenge food or carrion left behind by other animals.^[71] Grizzly bears will also eat birds and their eggs, and gather in large numbers at fishing sites to feed on spawning salmon. They frequently prey on baby deer left in the grass, and occasionally they raid the nests of raptors such as bald eagles.^[72]

Coastal Canadian and Alaskan grizzlies are larger than those that reside in the Rocky Mountains. This is due, in part, to the richness of their diets. In Yellowstone National Park in the United States, the grizzly bear’s diet consists mostly of whitebark pine nuts, tubers, grasses, various rodents, army cutworm moths, and scavenged carcasses.^[73] None of these, however, match the fat content of the salmon available in Alaska and British Columbia. With the high fat content of salmon, it is not uncommon to encounter grizzlies in Alaska weighing 540 kg (1,200 lb).^[74] Grizzlies in Alaska supplement their diet of salmon and clams with sedge grass and berries. In areas where salmon are forced to leap waterfalls, grizzlies gather at the base of the falls to feed on and catch the fish. Salmon are at a disadvantage when they leap waterfalls because they cluster together at their bases and are therefore easier targets for the grizzlies.^[75] Grizzly bears are well-documented catching leaping salmon in their mouths at Brooks Falls in Katmai National Park and Preserve in Alaska. They are also very experienced in chasing the fish around and pinning them with their claws.^[76] At such sites such as Brooks Falls and McNeil Falls in Alaska, big male grizzlies fight regularly for the best fishing spots.^[77] Grizzly bears along the coast also forage for razor clams, and frequently dig into the sand to seek them.^[78] During the spring and fall, directly before and after the salmon runs, berries and grass make up the mainstay of the diets of coastal grizzlies.^[79]

Inland grizzlies may eat fish too, most notably in Yellowstone grizzlies eating Yellowstone cutthroat trout.^[80] The relationship with cutthroat trout and grizzlies is unique because it is the only example where Rocky Mountain grizzlies feed on spawning salmonid fish.^[80] However, grizzly bears themselves and invasive lake trout threaten the survival of the trout population and there is a slight chance that the trout will be eliminated.^[81]

Grizzly bears occasionally prey on small mammals, such as marmots, ground squirrels, lemmings, and voles.^[82] The most famous example of such predation is in Denali National Park and Preserve, where grizzlies chase, pounce on, and dig up Arctic ground squirrels to eat.^[83] In some areas, grizzly bears prey on hoary marmots, overturning rocks to reach them, and in some cases preying on them when they are in hibernation.^[84] Larger prey includes bison and moose, which are sometimes taken by bears in Yellowstone National Park. Because bison and moose are dangerous prey, grizzlies usually use cover to stalk them and/or pick off weak individuals or calves.^[85][86] Grizzlies in Alaska also regularly prey on moose calves, which in Denali National Park may be their main source of meat. In fact, grizzly bears are such important predators of moose and elk calves in Alaska and Yellowstone that they may kill as many as 51 percent of elk or moose calves born that year. Grizzly bears have also been blamed in the decline of elk in Yellowstone National Park when the actual predators were thought to be gray wolves.^{[87][88][89][90][91]} In northern Alaska, grizzlies are a significant predator of caribou, mostly taking sick or old individuals or calves.^[92] Several studies show that grizzly bears may follow the caribou herds year-round in order to maintain their food supply.^[93][94] In northern Alaska, grizzly bears often encounter muskox. Despite the fact that muskox do not usually occur in grizzly habitat and that they are bigger and more powerful than caribou, predation on muskox by grizzlies has been recorded.^[95]

Grizzlies along the Alaskan coast also scavenge on dead or washed up whales.^[96] Usually such incidents involve only one or two grizzlies at a carcass, but up to ten large males have been seen at a time eating a dead humpback whale. Dead seals and sea lions are also consumed.^{[citation needed]}

Although the diets of grizzly bears vary extensively based on seasonal and regional changes, plants make up a large portion of them, with some estimates as high as 80–90%.^[97] Various berries constitute an important food source when they are available. These can include blueberries, blackberries (Rubus fruticosus), salmon berries (Rubus spectabilis), cranberries (Vaccinium oxycoccos), buffalo berries (Shepherdia argentea), soapberries (Shepherdia canadensis), and huckleberries (Vaccinium parvifolium), depending on the environment. Insects such as ladybugs, ants, and bees are eaten if they are available in large quantities. In Yellowstone National Park, grizzly bears may obtain half of their yearly caloric needs by feeding on miller moths that congregate on mountain slopes.^[98] When food is abundant, grizzly bears will feed in groups. For example, many grizzly bears will visit meadows right after an avalanche or glacier slide. This is due to an influx of legumes, such as Hedysarum, which the grizzlies consume in massive amounts.^[99] When food sources become scarcer, however, they separate once again.

Interspecific competition

The relationship between grizzly bears and other predators is mostly one-sided; grizzly bears will approach feeding predators to steal their kill. In general, the other species will leave the carcasses for the bear to avoid competition or predation. Any parts of the carcass left uneaten are scavenged by smaller animals.^[100]

Wolves

With the reintroduction of gray wolves to Yellowstone, many visitors have witnessed a once common struggle between a keystone species, the grizzly bear, and its historic rival, the gray wolf. The interactions of grizzly bears with the wolves of Yellowstone have been under considerable study. Typically, the conflict will be in the defence of young or over a carcass, which is commonly an elk killed by wolves.^[101]

The grizzly bear uses its keen sense of smell to locate the kill. As the wolves and grizzly compete for the kill, one wolf may try to distract the bear while the others feed. The bear then may retaliate by chasing the wolves. If the wolves become aggressive with the bear, it is normally in the form of quick nips at its hind legs. Thus, the bear will sit down and use its ability to protect itself in a full circle. Rarely do interactions such as these end in death or serious injury to either animal. One carcass simply is not usually worth the risk to the wolves (if the bear has the upper hand due to strength and size) or to the bear (if the wolves are too numerous or persistent).^[102]

While wolves usually dominate grizzly bears during interactions at wolf dens, both grizzly and black bears have been reported killing wolves and their cubs at wolf dens even when the wolves were acting in defence.^[103][104]

Big cats

Cougars generally give the bears a wide berth. Grizzlies have less competition with cougars than with other predators, such as coyotes, wolves, and other bears. When a grizzly descends on a cougar feeding on its kill, the cougar usually gives way to the bear. When a cougar does stand its ground, it will use its superior agility and its claws to harass the bear, yet stay out of its reach until one of them gives up. Grizzly bears occasionally kill cougars in disputes over kills.^[105] There have been several anecdotes, primarily from the late 19th and early 20th centuries, of cougars and grizzly bears killing each other in fights to the death.^[106]

The other big cat present in the United States which might pose a threat to bears is the jaguar;^[107] however, both species have been extirpated in the regions of the Southwest where their former habitats overlapped, and grizzlies remain so far absent from the regions along the U.S.-Mexico border, where jaguars appear to be returning.

Other bears

Black bears generally stay out of grizzly territory, but grizzlies may occasionally enter black bear terrain to obtain food sources both bears enjoy, such as pine nuts, acorns, mushrooms, and berries. When a black bear sees a grizzly coming, it either turns tail and runs or climbs a tree.

Black bears are not strong competition for prey because they have a more herbivorous diet. Confrontations are rare because of the differences in size, habitats, and diets of the bear species. When this happens, it is usually with the grizzly being the aggressor. The black bear will only fight when it is a smaller grizzly such as a yearling or when the black bear has no other choice but to defend itself. There is at least one confirmed observation of a grizzly bear digging out, killing, and eating a black bear when the latter was in hibernation.^[108]

The segregation of black bear and grizzly bear populations is possibly due to competitive exclusion. In certain areas, grizzly bears outcompete black bears for the same resources.^[109] For example, many Pacific coastal islands off British Columbia and Alaska support either the black bear or the grizzly, but rarely both.^[110]

In regions where they coexist, they are divided by landscape gradients such as the age of forest, elevation, and land openness. Grizzly bears tend to favor old forests with high productivity, higher elevations and more open habitats compared with black bears.^[109] However, a bear shot in autumn 1986 in Michigan was thought by some to be a grizzly–black bear hybrid, due to its unusually large size and its proportionately larger braincase and skull, but DNA testing was unable to determine whether it was a large American black bear or a grizzly bear.^[111]

Encounters between grizzly bears and polar bears have increased in recent times due to global warming. In encounters the grizzly is usually the more aggressive one and often dominate in fight.^[112] However, healthy polar bears seem to be dominant over the grizzly.^[113]

However, conflict is not the only result of the two bears meeting; in some instances grizzly–polar bear hybrids (called grolar bears or pizzly bears depending on the sex of the parents) are produced.^[114]

Various small predators

Coyotes, foxes, and wolverines are generally regarded merely as pests to grizzlies rather than competition, though they may compete for smaller prey, such as ground squirrels and rabbits. All three will try to scavenge whatever they can from the bears. Wolverines are aggressive enough to occasionally persist until the bear finishes eating, leaving more scraps than normal for the smaller animal.^[100] Packs of coyotes have also displaced grizzly bears in disputes over kills.^[115] However, the removal of wolves and grizzlies in California may have greatly reduced the abundance of the endangered San Joaquin Kit Fox.^[116]

Ecological role

Scent rubbing

The grizzly bear has several relationships with its ecosystem. One such relationship is a mutualistic relationship with fleshy-fruit bearing plants. After the grizzly consumes the fruit, the seeds are excreted and thereby dispersed in a germinable condition. Some studies have shown germination success is indeed increased as a result of seeds being deposited along with nutrients in feces.^[117] This makes grizzly bears important seed distributors in their habitats.^[118]

While foraging for tree roots, plant bulbs, or ground squirrels, bears stir up the soil. This process not only helps grizzlies access their food, but also increases species richness in alpine ecosystems.^[119] An area that contains both bear digs and undisturbed land has greater plant diversity than an area that contains just undisturbed land.^[119] Along with increasing species richness, soil disturbance causes nitrogen to be dug up from lower soil layers, and makes nitrogen more readily available in the environment. An area that has been dug by the grizzly bear has significantly more nitrogen than an undisturbed area.^[120]

Nitrogen cycling is not only facilitated by grizzlies digging for food, it is also accomplished via their habit of carrying salmon carcasses into surrounding forests.^[121] It has been found that spruce tree (Picea glauca) foliage within 500 m (1,600 ft) of the stream where the salmon have been obtained contains nitrogen originating from salmon on which the bears preyed.^[122] These nitrogen influxes to the forest are directly related to the presence of grizzly bears and salmon.^[123]

Grizzlies directly regulate prey populations and also help prevent overgrazing in forests by controlling the populations of other species in the food chain.^[124] An experiment in Grand Teton National Park in Wyoming in the United States showed removal of wolves and grizzly bears caused populations of their herbivorous prey to increase.^[125] This, in turn, changed the structure and density of plants in the area, which decreased the population sizes of migratory birds.^[125] This provides evidence grizzly bears represent a keystone predator, having a major influence on the entire ecosystem they inhabit.^[124]

When grizzly bears fish for salmon along the coasts of Alaska and British Columbia, they often only eat the skin, brain and roe of the fish. In doing so, they provide a food source for gulls, ravens, and foxes, all of which eat salmon as well; this benefits both the bear and the smaller predators.^[126]

Interaction with humans

Relationship with Native Americans

Native American tribes living among brown bears often view them with a mixture of awe and fear.^[127] North American brown bears have at times been so feared by the Natives that they were rarely hunted by them, especially when alone. At traditional grizzly hunts in some western tribes such as the Gwichʼin, the expedition was conducted with the same preparation and ceremoniality as intertribal warfare and was never done except with a company of four to ten warriors. The tribe members who dealt the killing blow were highly esteemed among their compatriots.^[128] Californian Natives actively avoided prime bear habitat and would not allow their young men to hunt alone for fear of bear attacks. During the Spanish colonial period, some tribes would seek aid from European colonists to deal with problem bears instead of hunting grizzlies themselves. Many authors in the American West wrote of Natives or voyageurs with lacerated faces and missing noses or eyes, due to attacks from grizzlies.^[129][130]

Many Native American tribes both respect and fear the brown bear.^{[128][130][131]} In Kwakiutl mythology, American black and brown bears became enemies when Grizzly Bear Woman killed Black Bear Woman for being lazy. Black Bear Woman’s children, in turn, killed Grizzly Bear Woman’s own cubs.^[132] Sleeping Bear Dunes is named after an Ojibwe legend, where a female bear and her cubs swam across Lake Michigan. According to the legend, the two cubs drowned and became the Manitou islands. The mother bear eventually got to shore and slept, waiting patiently for her cubs to arrive. Over the years, the sand covered the mother bear up, creating a huge sand dune.

Conflicts with humans

See also: Bear attack and List of fatal bear attacks in North America

Native Americans fighting two grizzly bears, 1844 painting by George Catlin

A rough and tumble with a grizzly by H. Bullock Webster, watercolor

Grizzlies are considered more aggressive compared to black bears when defending themselves and their offspring.^[133] Unlike the smaller black bears, adult grizzlies do not climb trees well, and respond to danger by standing their ground and warding off their attackers.^[134] Mothers defending cubs are the most prone to attacking, and are responsible for 70% of humans killed by grizzlies.^[135]

Grizzly bears normally avoid contact with people. In spite of their obvious physical advantage they rarely actively hunt humans.^[136] Most grizzly bear attacks result from a bear that has been surprised at very close range, especially if it has a supply of food to protect, or female grizzlies protecting their offspring.^[137]

Increased human–bear interaction has created “problem bears”: bears adapted to human activities or habitat.^[138] Exacerbating this is the fact that intensive human use of grizzly habitat coincides with the seasonal movement of grizzly bears.^[137] Aversive conditioning using rubber bullets, foul-tasting chemicals, or acoustic deterrent devices attempt to condition bears to associate humans with unpleasantness, but is ineffective when the bears have already learned to positively associate humans with food.^[139] Such bears are translocated or killed because they pose a threat to humans. The B.C. government kills approximately 50 problem bears each year^[139] and overall spends more than one million dollars annually to address bear complaints, relocate bears or kill them.^[139] A bear killing a human in a national park may be killed to prevent its attacking again.^[140]

Bear awareness programs have been developed by communities in grizzly bear territory to help prevent conflicts with both black and grizzly bears. The main premise of these programs is to teach humans to manage foods that attract bears. Keeping garbage securely stored, harvesting fruit when ripe, securing livestock behind electric fences, and storing pet food indoors are all measures promoted by bear awareness programs.^[141] Revelstoke, British Columbia, is a community that demonstrates the success of this approach. In the ten years preceding the development of a community education program in Revelstoke, 16 grizzlies were destroyed and a further 107 were relocated away from the town. An education program run by Revelstoke Bear Aware was put in place in 1996. Since the program began just four grizzlies have been eliminated and five have been relocated.^[142]

For back-country campers, hanging food between trees at a height unreachable to bears is a common procedure, although some grizzlies can climb and reach hanging food in other ways. An alternative to hanging food is to use a bear canister.^[143]

Traveling in groups of six or more can significantly reduce the chance of bear-related injuries while hiking in bear country.^[144] Grizzly bears are especially dangerous because of the force of their bite, which has been measured at over 8 megapascals (1160 psi). It has been estimated that a bite from a grizzly can crush a bowling ball.^[145]

Bear-watching

In the past 20 years in Alaska, ecotourism has boomed. While many people come to Alaska to bear-hunt, the majority come to watch the bears and observe their habits. Some of the best bear viewing in the world occurs on coastal areas of the Alaska Peninsula, including in Lake Clark National Park and Preserve, Katmai National Park and Preserve, and the McNeil River State Game Sanctuary and Refuge. Here bears gather in large numbers to feast on concentrated food sources, including sedges in the salt marshes, clams in the nearby tidal flats, salmon in the estuary streams, and berries on the neighboring hillsides.

Katmai National Park and Preserve is one of the best spots to view brown bears. As of 2012, the bear population in Katmai is estimated to be 2,100.^[146][147] The park is located on the Alaskan Peninsula about 480 km (300 mi) southwest of the city of Anchorage. At Brooks Camp, a famous site exists where grizzlies can be seen catching salmon from atop a platform–it can be even viewed online from a cam.^[148] In coastal areas of the park, such as Hallo Bay, Geographic Harbor, Swikshak Lagoon, American Creek, Big River, Kamishak River, Savonoski River, Moraine Creek, Funnel Creek, Battle Creek, Nantuk Creek,^[149] Kukak Bay, and Kaflia Bay bears can be seen fishing alongside wolves, eagles, and river otters. Coastal areas host the highest population densities year round because there is a larger variety of food sources available, but Brooks Camp hosts the highest population (100 bears).^[150]

The McNeil River State Game Sanctuary and Refuge, on the McNeil River, is home to the greatest concentration of brown bears in the world. An estimated 144 individual bears have been identified at the falls in a single summer with as many as 74 at one time;^[151] 60 or more bears at the falls is a frequent sight, and it is not uncommon to see 100 bears at the falls throughout a single day.^[152] The McNeil River State Game Refuge, containing Chenik Lake and a smaller number of grizzly bears, has been closed to grizzly hunting since 1995.^[153] All of the Katmai-McNeil area is closed to hunting except for Katmai National Preserve, where regulated legal hunting takes place.^[154] In all, the Katmai-McNeil area has an estimated 2,500 grizzly bears.^[155]

Admiralty Island, in southeast Alaska, was known to early natives as Xootsnoowú, meaning “fortress of bears,” and is home to the densest grizzly population in North America. An estimated 1600 grizzlies live on the island, which itself is only 140 km (90 mi) long.^[156] One place to view grizzly bears in the island is probably Pack Creek, in the Stan Price State Wildlife Sanctuary. 20 to 30 grizzlies can be observed at the creek at one time and like Brooks Camp, visitors can watch bears from an above platform.^[157] Kodiak Island, hence its name, is another place to view bears. An estimated 3,500 Kodiak grizzly bears inhabit the island, 2,300 of these in the Kodiak National Wildlife Refuge.^[158][159] The O’Malley River is considered the best place on Kodiak Island to view grizzly bears.^[160]

Protection

The grizzly bear is listed as threatened in the contiguous United States and endangered in parts of Canada. In May 2002, the Canadian Species at Risk Act listed the Prairie population (Alberta, Saskatchewan and Manitoba range) of grizzly bears as extirpated in Canada.^[161] As of 2002, grizzly bears were listed as special concern under the COSEWIC registry^[162] and considered threatened under the U.S. Fish and Wildlife Service.^[163]

Within the United States, the U.S. Fish and Wildlife Service concentrates its effort to restore grizzly bears in six recovery areas. These are Northern Continental Divide (Montana), Yellowstone (Montana, Wyoming, and Idaho), Cabinet-Yaak (Montana and Idaho),^[164] Selway-Bitterroot (Montana and Idaho), Selkirk (Idaho and Washington), and North Cascades (Washington). The grizzly population in these areas is estimated at 1,000 in the Northern Continental Divide, 1,000 in Yellowstone,^[165] 40 in the Yaak portion of the Cabinet-Yaak, and 15 in the Cabinet portion (in northwestern Montana), 105 in Selkirk region of Idaho, 10–20 in the North Cascades, and none currently in Selway-Bitterroots, although there have been sightings.^[166] These are estimates because bears move in and out of these areas. In the recovery areas that adjoin Canada, bears also move back and forth across the international boundary.

The U.S. Fish and Wildlife Service claims the Cabinet-Yaak and Selkirk areas are linked through British Columbia, a claim that is disputed.^[167] U.S. and Canadian national parks, such as Banff National Park, Yellowstone and Grand Teton, and Theodore Roosevelt National Park are subject to laws and regulations designed to protect the bears.

On 9 January 2006, the US Fish and Wildlife Service proposed to remove Yellowstone grizzlies from the list of threatened and protected species.^[168] In March 2007, the U.S. Fish and Wildlife Service “de-listed” the population,^[169] effectively removing Endangered Species Act protections for grizzlies in the Yellowstone National Park area. Several environmental organizations, including the NRDC, brought a lawsuit against the federal government to relist the grizzly bear. On 22 September 2009, U.S. District Judge Donald W. Molloy reinstated protection due to the decline of whitebark pine tree, whose nuts are an important source of food for the bears.^[170] In early March 2016, the U.S. Fish and Wildlife Service proposed to withdraw Endangered Species Act protections from grizzly bears in and around Yellowstone National Park. The population has risen from 136 bears in 1975 to an estimated 700 in 2017, and was “delisted” in June 2017.^{[171][172][173]} It was argued that the population had sufficiently recovered from the threat of extinction, however numerous conservation and tribal organizations argued that the grizzly population remained genetically vulnerable. They successfully sued the administration (Crow Tribe et al v. Zinke) and on 30 July 2019, the Yellowstone grizzly was officially returned to federal protection.^[174][175]

In Alberta, Canada, intense DNA hair-snagging studies in 2000 showed the grizzly population to be increasing faster than what it was formerly believed to be, and Alberta Sustainable Resource Development calculated a population of 841 bears.^[176] In 2002, the Endangered Species Conservation Committee recommended that the Alberta grizzly bear population be designated as threatened due to recent estimates of grizzly bear mortality rates that indicated the population was in decline. A recovery plan released by the provincial government in March 2008 indicated the grizzly population is lower than previously believed.^[177] In 2010, the provincial government formally listed its population of about 700 grizzlies as “Threatened”.^[178]

Environment Canada consider the grizzly bear to a “special concern” species, as it is particularly sensitive to human activities and natural threats. In Alberta and British Columbia, the species is considered to be at risk.^[179] In 2008, it was estimated there were 16,014 grizzly bears in the British Columbia population, which was lower than previously estimated due to refinements in the population model.^[180]

Conservation efforts

Conservation efforts have become an increasingly vital investment over recent decades, as population numbers have dramatically declined. Establishment of parks and protected areas are one of the main focuses currently being tackled to help reestablish the low grizzly bear population in British Columbia. One example of these efforts is the Khutzeymateen Grizzly Bear Sanctuary located along the north coast of British Columbia; at 44,300 ha (109,000 acres) in size, it is composed of key habitat for this threatened species. Regulations such as limited public access, as well as a strict no hunting policy, have enabled this location to be a safe haven for local grizzlies in the area.^[181] When choosing the location of a park focused on grizzly bear conservation, factors such as habitat quality and connectivity to other habitat patches are considered.

The Refuge for Endangered Wildlife located on Grouse Mountain in Vancouver is an example of a different type of conservation effort for the diminishing grizzly bear population. The refuge is a five-acre terrain which has functioned as a home for two orphaned grizzly bears since 2001.^[182] The purpose of this refuge is to provide awareness and education to the public about grizzly bears, as well as providing an area for research and observation of this secluded species.

Another factor currently being taken into consideration when designing conservation plans for future generations are anthropogenic barriers in the form of urban development and roads. These elements are acting as obstacles, causing fragmentation of the remaining grizzly bear population habitat and prevention of gene flow between subpopulations (for example, Banff National Park). This, in turn, is creating a decline in genetic diversity, and therefore the overall fitness of the general population is lowered.^[183] In light of these issues, conservation plans often include migration corridors by way of long strips of “park forest” to connect less developed areas, or by way of tunnels and overpasses over busy roads.^[184] Using GPS collar tracking, scientists can study whether or not these efforts are actually making a positive contribution towards resolving the problem.^[185] To date, most corridors are found to be infrequently used, and thus genetic isolation is currently occurring, which can result in inbreeding and therefore an increased frequency of deleterious genes through genetic drift.^[186] Current data suggest female grizzly bears are disproportionately less likely than males to use these corridors, which can prevent mate access and decrease the number of offspring.^{[citation needed]}

In the United States, national efforts have been made since 1982 for the recovery plan of grizzly bears.^[187] The Interagency Grizzly Bear Recovery Committee is one of many organizations committed to the recovery of grizzly bears in the lower 48 states.^[188] There are five recovery zones for grizzly bears in the lower 48 states including the North Cascades ecosystem in Washington state.^[171] The National Park Service and U.S. Fish and Wildlife initiated the process of an environmental impact statement in the fall of 2014 to begin the recovery process of grizzly bears to the North Cascades region.^[171] A final plan and environmental impact statement was released in the spring of 2017 with a record of decision to follow.^[171][173]

In 2017, the Trump administration stripped parklands of previous regulations that protected wildlife living on the land, putting species such as the grizzly bear at risk.^[189] Specifically, federal protections on the grizzly bear in Yellowstone National Parks were removed. Regulations that protected the bears against hunting methods with Park Service rules (specifically in park lands in Alaska) were revisited by the Department of Interior.^[189][190] The National Parks Conservation Association (NPCA) supports common sense opportunities for hunting in national preserves,” but the state of Alaska’s wildlife management leads for the killing of more bears, which increases the population of moose and caribou.^[189][190] The rise in moose and caribou works in favor of sport hunters. Theresa Pierno, President and CEO of National Parks Conservation Association stated, “The State of Alaska’s lawsuit against the Park Service and Fish and Wildlife Service seeks to overturn common sense regulations, which underwent a thorough and transparent public process. More than 70,000 Americans said ‘no’ to baiting bears with grease-soaked donuts in Denali National Park and Preserve. The public was right to want to stop sport hunters from crawling into bears’ dens and using flashlights to wake and kill mother bears and their cubs. The state’s attempt to dismantle the results of this public process jeopardizes the stewardship of federal public lands, which belong to all Americans.”^[189]

A press release on 3 October 2022, stated that a federal district court, based in Alaska, will be returning to look over a National Park Service rule relating to hunting practices, including baiting bears.^[189] The Interior Department and Park Service’s decision permits the law to reside in place while conducting revisions.^[