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Lifespan, longevity, and ageing

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Maximum longevity: 20 years
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Behavior

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American Crows are highly vocal birds. Unlike most other songbirds, males and females have the same songs. They have a complex system of loud, harsh caws that are often uttered in repetitive rhythmic series. Shorter and sharper caws called "kos" are probably alarm or alert calls. Slightly longer caws are probably used in territorial defense, and patterns of repetition may be matched in what may be considered "countersinging," or exchanges between territorial neighbors. "Double caws," short caws repeated in stereotyped doublets, may serve as a call-to-arms vocalization, alerting family members to territorial intruders. Sometimes pairs or family members coordinate their cawing in a duet or chorus. Harsher cawing is used while mobbing potential predators.

People are less familiar with the large variety of softer calls crows can make. Melodic, highly variable coos accompanied by bowing postures are used among family members, possibly as greetings or other bonding signals. Coos of cage-mates become similar over time; this vocalization may therefore be the basis of the mimicry ability shown by pet crows. Crows also give several kinds of rattles.

Young crows make gargling sounds that eventually turn into adult vocalizations. Yearling crows also "ramble" or run through long sequences of different patterns and rhythms of cawing.

Communication Channels: visual ; acoustic

Perception Channels: visual ; tactile ; acoustic ; chemical

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Parr, C. 2005. "Corvus brachyrhynchos" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Corvus_brachyrhynchos.html
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Conservation Status

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American crows are thriving, particularly in association with suburban areas. Their numbers may be increasing.

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

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Benefits

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Large foraging flocks of American crows may impact agriculture, particularly orchards and cornfields. In the United States there once was a bounty on them. People often consider large roosts to be nuisances when they occur in areas with high human activity; there is concern about noise, mess, and disease from feces. American crows can scatter garbage. As nest predators they may negatively impact population of game birds such as ducks.

Negative Impacts: crop pest

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Benefits

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Although American crows can be harmful to crops, their impact is shown to be less than what it was previously thought to be. Damage to crops is offset by the amount of damage prevented because the crows eat insect pests. Though it is illegal under the Migratory Bird Act, many people have kept young crows as pets and they are known to mimic human speech. American crows are also considered small game, and hunting seasons exist in many states. Typically they are hunted for sport at times when more valuable game birds cannot be hunted.

Positive Impacts: controls pest population

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Associations

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American crows do not have significant, unique roles in particular ecosystems. They probably serve as seed dispersers as they eat fruit and cache nuts. They scavenge on carcasses which speeds their decomposition.

Ecosystem Impact: disperses seeds; biodegradation

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Parr, C. 2005. "Corvus brachyrhynchos" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Corvus_brachyrhynchos.html
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Trophic Strategy

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American crows are omnivores and will eat almost anything. During the breeding season, American crows consume insects and their larvae, worms, fruits, grains, and nuts. They actively hunt and prey on small animals such as frogs, mice, and young rabbits, though they more likely to scavenge carrion such as roadkill. They also are significant nest predators, preying on the eggs and nestlings of smaller songbirds. In the fall and winter they eat more nuts, such as walnuts and acorns. On rare occasions, American crows will eat from bird feeders put out by humans. Crows often take advantage of human garbage.

American crows store food items such as meat and nuts in short-term caches. Caches are hiding places that are scattered around, rather than in one place. They may be in tree crevices or on the ground, where they are often covered with leaves or other material.

Crows forage primarily by walking on the ground and picking up the item, or by walking along tree branches. Foraging is usually done by a few individuals in a small area, but can also occur in groups over a larger area.

Crows will hold a nut under one foot and strike it with the bill to open it. To open a particularly heavy-shelled food item such as a walnut or clam, a crow will fly high with it and drop it on a hard surface.

Animal Foods: birds; mammals; amphibians; reptiles; eggs; carrion ; insects; terrestrial non-insect arthropods; mollusks; terrestrial worms

Plant Foods: seeds, grains, and nuts; fruit

Primary Diet: omnivore

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Parr, C. 2005. "Corvus brachyrhynchos" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Corvus_brachyrhynchos.html
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Distribution

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American crows are native to the Nearctic region all over North America. They can be found in the lower part of Canada and through the continental United States.

Biogeographic Regions: nearctic (Native )

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Parr, C. 2005. "Corvus brachyrhynchos" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Corvus_brachyrhynchos.html
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Habitat

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American crows prefer open areas with nearby trees. Agricultural and grassland areas are ideal habitat for crows to forage for their food. American crows will also use nearby woodlots and forest edges for breeding and roosting. American crows thrive in suburban neighborhoods and urban parks, as well as in coastal habitats.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: savanna or grassland ; forest ; scrub forest

Aquatic Biomes: coastal

Other Habitat Features: urban ; suburban ; agricultural ; riparian ; estuarine

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Parr, C. 2005. "Corvus brachyrhynchos" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Corvus_brachyrhynchos.html
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Life Expectancy

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The oldest recorded age of a wild American crow is 14 years and 7 months.

Range lifespan
Status: wild:
14 (high) years.

Average lifespan
Status: wild:
175 months.

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Parr, C. 2005. "Corvus brachyrhynchos" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Corvus_brachyrhynchos.html
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Morphology

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Adult American crows are completely black birds weighing on average 450 g. The feathers have a glossy and slightly iridescent look. Crows have strong legs and toes. The bill is also black with a slight hook on the end. Stiff bristles cover their nostrils. About 20% of male birds are slightly larger than the females.

Young crows are about the same size as adults, but have blue eyes and pink inside the mouth. Both the eyes and mouth darken as the bird becomes an adult. In young birds, the ends of tail feathers are symmetrical and are more pointed than the wide, flat-ended feathers of adults. The wing and tail feathers of the young can become quite brown and ragged through the first winter and spring and only become darker and more glossy like adult feathers after the first molt.

American crows are often confused with common ravens. American crows can be distinguished from common ravens (Corvus corax) most easily by size (ravens are much larger), by voice (ravens are hoarser), by the bill (ravens have heavier, "roman-nosed" bills), and by the shape of the wings and tails, which come to a point in ravens but not crows.

Average mass: 450 g.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes alike; male larger

Average mass: 384.8 g.

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Associations

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Crows will group together to vocally harass and chase predators. This behavior is called mobbing.

Known Predators:

  • red-tailed hawks
  • great horned owls
  • raccoons
  • humans
  • snakes
  • domestic cats
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Parr, C. 2005. "Corvus brachyrhynchos" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Corvus_brachyrhynchos.html
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Reproduction

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Breeding in American crows may begin as early as February and last through June. Nests are usually built by both males and females high in a sturdy conifer or hardwood tree. Females lay 4 to 5 light green colored eggs with brown markings. The female incubates her eggs, which means that she sits on them to keep the eggs warm until they hatch. Eggs hatch after 18 days. While she is sitting on the nest, the female will beg for food like a baby bird, and her mate will bring it to her. The young fledge (leave the nest) when they are approximately 35 days old. Most American crows reach sexual maturity and begin to breed when they are two years old.

Breeding interval: American crows rear only a single brood each year; if a nest fails early in the breeding season the pair may try to lay a second clutch of eggs.

Breeding season: Breeding occurs from February through June.

Range eggs per season: 4 to 5.

Average eggs per season: 4.

Average time to hatching: 18.0 days.

Average fledging age: 35.0 days.

Average age at sexual or reproductive maturity (female): 2.0 years.

Average age at sexual or reproductive maturity (male): 2.0 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; oviparous

Average time to hatching: 18 days.

Average eggs per season: 5.

Young crows are helpless at birth and require parental care. They are fed by both parents as well as by helpers who are their older siblings. After they leave their nests, young are still clumsy for several weeks and must be fed and protected by family members during the summer. Parents have been observed to feed babies even after they can find food on their own.

Parental Investment: altricial ; pre-fertilization (Protecting: Male, Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)

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Corvus brachyrhynchos

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Only slightly larger (17-21 inches) than the similar-looking Fish Crow (Corvus ossifragus), the American Crow is most easily separated from its relative by its call, which is deeper and less nasal than that of the Fish Crow. Other field marks include a glossy purple-black body, thick bill, and slightly rounded tail. The American Crow occurs widely across the United States and southern Canada, absent only from the desert southwest, south Texas and northwestern Washington (where it is replaced by the Northwestern Crow, Corvus caurinus). Many American Crows breeding in Canada move south into the U.S. during the winter. However, more southerly populations are mostly non-migratory. American Crows tend to avoid wide expanses of open country such as desert, grassland, and tundra. Otherwise, American Crows are extremely adaptable birds, and are found in many habitats across North America, including forest, orchards, fields, suburbs, and even inner cities. Likewise, this species eats a variety of plant and animal foods, including fruits, seeds, small mammals, carrion, and garbage. Like most members of the crow family, the American Crow is extremely sociable. American Crows gather together in family groups to feed, roost, and defend territory. They will even mob larger predatory birds intruding on their territory, swooping down and calling loudly until the predator leaves the area. This species is primarily active during the day.

Threat Status: Least Concern

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Corvus brachyrhynchos

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Only slightly larger (17-21 inches) than the similar-looking Fish Crow (Corvus ossifragus), the American Crow is most easily separated from its relative by its call, which is deeper and less nasal than that of the Fish Crow. Other field marks include a glossy purple-black body, thick bill, and slightly rounded tail. The American Crow occurs widely across the United States and southern Canada, absent only from the desert southwest, south Texas and northwestern Washington (where it is replaced by the Northwestern Crow,Corvus caurinus). Many American Crows breeding in Canada move south into the U.S. during the winter. However, more southerly populations are mostly non-migratory. American Crows tend to avoid wide expanses of open country such as desert, grassland, and tundra. Otherwise, American Crows are extremely adaptable birds, and are found in many habitats across North America, including forest, orchards, fields, suburbs, and even inner cities. Likewise, this species eats a variety of plant and animal foods, including fruits, seeds, small mammals, carrion, and garbage. Like most members of the crow family, the American Crow is extremely sociable. American Crows gather together in family groups to feed, roost, and defend territory. They will even mob larger predatory birds intruding on their territory, swooping down and calling loudly until the predator leaves the area. This species is primarily active during the day.

References

  • American Crow (Corvus brachyrhynchos). The Internet Bird Collection. Lynx Edicions, n.d. Web. 20 July 2012.
  • Corvus brachyrhynchos. Xeno-canto. Xeno-canto Foundation, n.d. Web. 20 July 2012.
  • Verbeek, N. A. and C. Caffrey. 2002. American Crow (Corvus brachyrhynchos), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/647
  • eBird Range Map - American Crow. eBird. Cornell Lab of Ornithology, N.d. Web. 20 July 2012.

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Rumelt, Reid B. Corvus brachyrhynchos. June-July 2012. Brief natural history summary of Corvus brachyrhynchos. Smithsonian's National Museum of Natural History, Washington, D.C.
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American crow

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Pair of crows chasing away a red-tailed hawk from their nest

The American crow (Corvus brachyrhynchos) is a large passerine bird species of the family Corvidae. It is a common bird found throughout much of North America. American crows are the New World counterpart to the carrion crow and the hooded crow. Although the American crow and the hooded crow are very similar in size, structure and behavior, their calls and visual appearance are different. The American crow, nevertheless, occupies the same ecological niche that the hooded crow and carrion crow do in Eurasia.

From beak to tail, an American crow measures 40–50 cm (16–20 in), almost half of which is tail. Mass varies from about 300 to 600 g (11 to 21 oz). Males tend to be larger than females. The most usual call is CaaW!-CaaW!-CaaW!. Plumage is all black, with iridescent feathers. It looks much like other all-black corvids. They can be distinguished from the common raven (C. corax) because American crows are smaller; from the fish crow (C. ossifragus) because American crows do not hunch and fluff their throat feathers when they call; and from the carrion crow (C. corone) by size, as the carrion crow is larger and of a stockier build. They are very intelligent, and adaptable to human environments.

American crows are common, widespread, and susceptible to the West Nile virus, making them useful as a bioindicator to track the virus's spread. Direct transmission of the virus from crows to humans is impossible. They are considered an agricultural pest, and are subject to hunting and management.

Taxonomy and systematics

The American crow was described by German ornithologist Christian Ludwig Brehm in 1822.[2] Its scientific name means literally 'short-billed crow', from Ancient Greek βραχυ- brachy- ('short-') and ρυνχος rhynchos ('billed').[3]

A 2012 genetic analysis of the genus Corvus by Knud A Jønsson and colleagues using nuclear and mitochondrial DNA calculated that the American crow diverged from a lineage that gave rise to the collared, carrion and hooded crows around 5 million years ago.[4]

"American crow" has been designated the official name by the International Ornithologists' Union (IOC).[5]

Subspecies

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Northwestern crow range map

The number of subspecies varies by authority, ranging between three and five. The unclear taxonomy of the northwestern crow, previously its own species, has complicated subspecies determinations. Subspecies differ in bill proportion and form a rough NE–SW clinal in size across North America. Birds are smallest in the far west and on the southern coast.[6][2]

  • C. b. brachyrhynchos (Brehm, 1822)eastern crow: northeastern United States, eastern Canada and surroundings. The nominate subspecies, and largest.
  • C. b. hesperis (Ridgway, 1887)western crow: western North America except the Arctic north, the Pacific Northwest and the extreme south. Smaller overall with a proportionally more slender bill[7] and low-pitched voice.
  • C. b. caurinus (Baird, 1858) northwestern crow: of the Pacific temperate rain forests was formerly considered a distinct species as C. b. caurinus, averaging smaller in size than other American crows with a distinctly hoarser call.[8] It forms a hybrid swarm with American crow (sensu stricto) in coastal Washington and British Columbia.[9] The American Ornithological Society lumped the northwestern crow with the American crow in 2020.[10] It is now considered a geographic variation within C. b. hesperis.[11]
  • C. b. pascuus (Coues, 1899)Florida crow: Florida. Mid-sized, short-winged, but decidedly long bill and legs.[7]
  • C. b. paulus (Howell, 1913)southern crow: southern United States. Smaller overall, bill also small.[12]

Description

An American crow making its distinctive call.
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American crow - Brooklyn, NY
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The skull of an American crow

The American crow is a large, distinctive bird with iridescent black feathers all over. Its legs, feet and bill are also black. They measure 40–53 cm (16–21 in) in length, of which the tail makes up about 40%. The wing chord is 24.5 to 33 cm (9.6 to 13.0 in), with the wingspan ranging from 85 to 100 cm (33 to 39 in). The bill length can be from 3 to 5.5 cm (1.2 to 2.2 in), varying strongly according to location. The tarsus is 5.5 to 6.5 cm (2.2 to 2.6 in) and the tail is 13.5 to 19 cm (5.3 to 7.5 in).[6] The body mass can vary from 316 to 620 g (11.1 to 21.9 oz). Males tend to be larger than females.[13][14]

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Brooklyn Museum - American crow - John J. Audubon

The most usual call is a loud, short, and rapid caaw-caaw-caaw. Usually, the birds thrust their heads up and down as they utter this call. American crows can also produce a wide variety of sounds and sometimes mimic noises made by other animals, including other birds such as barred owls.[15]

Visual differentiation from the fish crow (C. ossifragus) is extremely difficult and often inaccurate. Nonetheless, differences apart from size do exist. Fish crows tend to have more slender bills and feet. There may also be a small sharp hook at the end of the fish crow's upper bill. Fish crows also appear as if they have shorter legs when walking. More dramatically, when calling, fish crows tend to hunch and fluff their throat feathers.

If seen flying at a distance from where size estimates are unreliable, the distinctly larger common ravens (C. corax) can be distinguished by their almost lozenge-shaped tail and their larger-looking heads. They also fluff their throat feathers when calling — like fish crows, only more so. Ravens also soar for extended periods, unlike crows, which rarely fly more than a few seconds without flapping their wings.

Crows have been noted to be intelligent. They have the same brain-weight-to-body ratio as humans. This has led to some studies that have identified that crows are self-aware and that young crows take time to learn from tolerant parents. While a human has a neocortex, the crow has a different area in their brain that is equally complex.[16][17]

Bird on a human's hand
A fledgling, of the Northwestern subtype

The average lifespan of the American crow in the wild is 7–8 years. Captive birds are known to have lived up to 30 years.[18]

Distribution and habitat

The range of the American crow now extends from the Pacific Ocean to the Atlantic Ocean in Canada, on the French islands of Saint-Pierre and Miquelon, south through the United States, and into northern Mexico.[1] The increase in trees throughout the Great Plains during the past century due to fire suppression and tree planting facilitated range expansions of the American crow[19] as well as range expansions of many other species of birds.[20][21][22] Virtually all types of country from wilderness, farmland, parks, open woodland to towns and major cities are inhabited; it is absent only from tundra habitat, where it is replaced by the common raven. This crow is a permanent resident in most of the US, but most Canadian birds migrate some distances southward in winter. Outside of the nesting season these birds often gather in large (thousands or even millions[23]) communal roosts at night.

The American crow was recorded in Bermuda from 1876 onwards.[24]

Behavior and ecology

Studying the behavior of American crows is laborious due to the difficulty in catching them to band them, let alone catching them again. Thus much of their behavior, including daily routine, migration, molting, survivorship, age of first breeding, nestling development, nature of nesting helpers, and more remains poorly studied.[2]

Diet

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American crow skeleton (Museum of Osteology)

The American crow is omnivorous. It will feed on invertebrates of all types, carrion, scraps of human food, nuts such as walnuts and almonds, seeds, eggs and nestlings, stranded fish on the shore and various grains. American crows are active hunters and will prey on mice, frogs, and other small animals. In the winter and autumn, the diet of American crows is more dependent on nuts and acorns. Occasionally, they will visit bird feeders.[25] The American crow is one of only a few species of bird that has been observed modifying and using tools to obtain food.[26]

Like most crows, they will scavenge at landfills, scattering garbage in the process. Where available, corn, wheat and other crops are a favorite food. These habits have historically caused the American crow to be considered a nuisance. However, it is suspected that the harm to crops is offset by the service the American crow provides by eating insect pests.[25]

Reproduction

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An American crow egg, in the collection of the Children's Museum of Indianapolis

American crows are socially monogamous cooperative breeding birds. Mated pairs form large families of up to 15 individuals from several breeding seasons that remain together for many years.[27] Offspring from a previous nesting season will usually remain with the family to assist in rearing new nestlings. American crows do not reach breeding age for at least two years.[28] Most do not leave the nest to breed for four to five years.[27]

The nesting season starts early, with some birds incubating eggs by early April.[29] American crows build bulky stick nests, nearly always in trees but sometimes also in large bushes and, very rarely, on the ground. They will nest in a wide variety of trees, including large conifers, although oaks are most often used. Three to six eggs are laid and incubated for 18 days. The young are usually fledged by about 36 days after hatching. Predation primarily occurs at the nest site and eggs and nestlings are frequently eaten by snakes, raccoons, ravens and domestic cats. Adults are less frequently predated, but face potential attack from great horned owls, red-tailed hawks, peregrine falcons and eagles. They may be attacked by predators such as coyotes or bobcats at carrion when incautious, although this is even rarer.[25][30]

West Nile virus

American crows succumb easily to West Nile virus infection. This was originally a mosquito-borne African virus causing encephalitis in humans and livestock since about 1000 AD, and was accidentally introduced to North America in 1999, apparently by an infected air traveller who got bitten by a mosquito after arrival. It is estimated that the American crow population has dropped by up to 45% since 1999.[31] Despite this decline, the crow is considered a species of least concern.[32] The disease runs most rampant in the subtropical conditions which encourage reproduction of its mosquito vectors among which Culex tarsalis is most significant. Mortality rates appear to be higher than those in other birds, causing local population losses of up to 72% in a single season.[28][33] Because of this, American crows are a sentinel species indicating the presence of West Nile virus in an area. Crows cannot transmit the virus to humans directly.[18]

Intelligence

American crows, like other corvids, are highly cunning and inquisitive. They are able to steal food from other species, often in creative ways. One example shows a group of crows stealing a fish from a Northern river otter: one bird pecked the otter's tail to distract it while other birds swooped in and stole the fish.[2] They are able to use and modify tools.[34]

Relationship with humans

Crows are a motif in human culture, often associated with death, thieves, graveyards, bad luck, and other negative connotations.[35]

Status and management

The intelligence and adaptability of the American crow has insulated it from threats, and it is instead considered an agricultural pest.[2] In 2012, BirdLife International estimated the American crow population to be around 31 million. The large population and vast range result in the least concern status for the American crow, meaning that the species is not threatened with extinction.[1]

Crows have been killed in large numbers by humans, both for recreation and as part of organized campaigns of extermination.[36] In Canada, American crows have no protections, aside from Quebec which bans their hunting during the nesting season.[2] Laws on their hunting vary throughout the United States. New Jersey allows for a limited hunting season, unless if they are agricultural pests in which case they may be killed. Oklahoma allows hunting even during the nesting season. In the first half of the 20th century, state sponsored campaigns dynamited roosting areas, taking large numbers of crows. A campaign in Oklahoma from 1934 to 1945 dynamited 3.8 million birds. The effect on populations was negligible and damage to agricultural crops did not decrease, and thus the campaign was halted as ineffective. In a study taking data from 1917 to 1999, intentional killings were the overwhelming cause of death for crows, accounting for 68% of all recovered bird bands.[2]

Non-deadly methods of managing crows are varied but usually limited in their effectiveness. High value crops may be netted, but this is cost prohibitive for most other crops. Frightening may be used to disperse crows, including loud noises from guns, fake hawks flown from balloons, fake owls that move with the wind, strips of reflective tape on fences, or recordings of crow distress calls. Poisoned baits are of limited effectiveness, as the most toxic baits are necessary but are generally unacceptable for use. Crows quickly learn to avoid less toxic baits, as the baits make crows sick. The actual effect of crows on agriculture has been poorly studied.[2] There is some suggestion that they may be a benefit to farmers, by eating insect pests and chasing off livestock predators like hawks.[35]

References

  1. ^ a b c BirdLife International (2018). "Corvus brachyrhynchos". IUCN Red List of Threatened Species. 2018: e.T22705990A131945410. doi:10.2305/IUCN.UK.2018-2.RLTS.T22705990A131945410.en. Retrieved 19 November 2021.
  2. ^ a b c d e f g h Verbeek, N. A.; Caffrey, Carolee (August 2021). Poole, A. F.; Gill, F. B. (eds.). "American Crow (Corvus brachyrhynchos) version 1.1". Birds of the World. Cornell Lab of Ornithology. doi:10.2173/bow.amecro.01.1.
  3. ^ Liddell, Henry George; Scott, Robert; Stuart-Jones, Henry and McKenzie, Roderick: (1980): A Greek-English Lexicon (abridged ed.). Oxford University Press, Oxford, UK. ISBN 0-19-910207-4.
  4. ^ Jønsson, Knud A.; Fabre, Pierre-Henri; Irestedt, Martin (2012). "Brains, tools, innovation and biogeography in crows and ravens". BMC Evolutionary Biology. 12: 72. doi:10.1186/1471-2148-12-72. PMC 3480872. PMID 22642364.
  5. ^ Gill, Frank; Donsker, David, eds. (2021). "Crows, mudnesters, melampittas, Ifrit, birds-of-paradise". World Bird List Version 11.2. International Ornithologists' Union. Retrieved 26 October 2021.
  6. ^ a b Madge, Steve & Burn, Hilary (1994): Crows and jays: a guide to the crows, jays and magpies of the world. A&C Black, London. ISBN 0-7136-3999-7.
  7. ^ a b Goodwin & Gillmor (1976): p. 87
  8. ^ Dick, Gary Owen (2007): American Crow. Whatbird.com – Field Guide to Birds of North America. identify.whatbird.com/obj/103/_/American_Crow.aspx Retrieved 2007-October-18.
  9. ^ Slager, David L.; Epperly, Kevin L.; Ha, Renee R.; Rohwer, Sievert; Wood, Chris; Hemert, Caroline; Klicka, John (2020). "Cryptic and extensive hybridization between ancient lineages of American crows". Molecular Ecology. 29 (5): 956–969. doi:10.1111/mec.15377. ISSN 0962-1083.
  10. ^ Chesser, R Terry; Billerman, Shawn M; Burns, Kevin J; Cicero, Carla; Dunn, Jon L; Kratter, Andrew W; Lovette, Irby J; Mason, Nicholas A; Rasmussen, Pamela C; Remsen, J V; Stotz, Douglas F (2020-07-24). "Sixty-first Supplement to the American Ornithological Society's Check-list of North American Birds". The Auk. 137 (3): ukaa030. doi:10.1093/auk/ukaa030. ISSN 0004-8038.
  11. ^ "Corvus brachyrhynchos hesperis (caurinus or occidentalis) (American Crow (caurinus or occidentalis)) - Avibase". avibase.bsc-eoc.org. Retrieved 2021-10-19.
  12. ^ Goodwin & Gillmor (1976) p. 88.
  13. ^ Kilham, Lawrence. The American Crow and the Common Raven. p. 52
  14. ^ American Crow, Life History, All About Birds – Cornell Lab of Ornithology. Allaboutbirds.org. Retrieved on 2013-03-06.
  15. ^ Lawrence Kilham (October 1990). The American Crow and the Common Raven. Texas A&M University Press. pp. 62–. ISBN 978-0-89096-466-8.
  16. ^ Amanda Heidt. "Like humans, these big-brained birds may owe their smarts to long childhoods".
  17. ^ Chris Baraniuk. "Crows have long been considered cunning. But their intelligence may be far more advanced than we ever thought possible".
  18. ^ a b Connecticut Department of Environmental Protection (2001): American Crow Fact Sheet Archived November 5, 2006, at the Wayback Machine. Version of 2001. Retrieved 2006-October-25.
  19. ^ Houston S. 1977. Changing patterns of Corvidae on the prairies. Blue Jay 35:149–155.
  20. ^ Livezey KB. 2009a. Range expansion of Barred Owls, part I: chronology and distribution. American Midland Naturalist 161:49–56.
  21. ^ Livezey KB. 2009b. Range expansion of Barred Owls, part 2: facilitating ecological changes. American Midland Naturalist 161:323–349.
  22. ^ Livezey KB. 2010. Killing barred owls to help spotted owls II: implications for many other range-expanding species. Northwestern Naturalist 91:251–270.
  23. ^ Di Dilvestro, Roger. "Something To Crow About". National Wildlife Federation.
  24. ^ Long, John L. (1981). Introduced Birds of the World: The worldwide history, distribution and influence of birds introduced to new environments. Terrey Hills, Sydney: Reed. p. 354. ISBN 0-589-50260-3.
  25. ^ a b c C. Parr (2005). "Corvus brachyrhynchos". Animal Diversity Web. Retrieved 13 September 2015.
  26. ^ Caffrey, Carolee (2000). "Tool Modification and Use by an American Crow". Wilson Bull. 112 (2): 283–284. doi:10.1676/0043-5643(2000)112[0283:TMAUBA]2.0.CO;2.
  27. ^ a b Roger Segelken: Tree-climbing researcher knows exactly how far the crow flies Archived September 16, 2006, at the Wayback Machine Cornell Chronicle. Retrieved 2006-October-25,
  28. ^ a b Cornell Lab of Ornithology (2002): Bird Guide – American Crow. Retrieved 2006-October-24.
  29. ^ Henninger, W.F. (1906). "A preliminary list of the birds of Seneca County, Ohio" (PDF). Wilson Bulletin. 18 (2): 47–60.
  30. ^ Johnson, Ron American Crows Archived 2017-07-16 at the Wayback Machine. Internet Center for Wildlife Damage Management
  31. ^ LaDeau, Shannon L.; Kilpatrick, A. Marm; Marra, Peter P. (2007). "West Nile virus emergence and large-scale declines of North American bird populations". Nature. 447 (7145): 710–713. doi:10.1038/nature05829. PMID 17507930.
  32. ^ Deen, David (December 12, 2012). "The crow – a sociable bird with a long memory". The Chronicle. Barton, Vermont. p. 34.
  33. ^ Caffrey, Carolee; Smith, Shauna C.R.; Weston, Tiffany J. (2005). "West Nile Virus Devastates an American Crow Population". Condor. 107 (1): 128–132. doi:10.1650/7646.
  34. ^ Caffrey, Carolee (June 2000). "Tool Modification and Use by an American Crow". The Wilson Bulletin. 112 (2): 283–284. doi:10.1676/0043-5643(2000)112[0283:TMAUBA]2.0.CO;2. ISSN 0043-5643.
  35. ^ a b Sullivan, Emily. "The Glorious American Crow - Romanticism at SU". Archived from the original on 2020-09-28. Retrieved 2021-10-23.
  36. ^ Campbell, Robert Wayne & Canadian Wildlife Service (1997). "American Crow". The Birds of British Columbia: Passerines : flycatchers through vireos. UBC Press. p. 227. ISBN 978-0-7748-0572-8.
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American crow: Brief Summary

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 src= Pair of crows chasing away a red-tailed hawk from their nest

The American crow (Corvus brachyrhynchos) is a large passerine bird species of the family Corvidae. It is a common bird found throughout much of North America. American crows are the New World counterpart to the carrion crow and the hooded crow. Although the American crow and the hooded crow are very similar in size, structure and behavior, their calls and visual appearance are different. The American crow, nevertheless, occupies the same ecological niche that the hooded crow and carrion crow do in Eurasia.

From beak to tail, an American crow measures 40–50 cm (16–20 in), almost half of which is tail. Mass varies from about 300 to 600 g (11 to 21 oz). Males tend to be larger than females. The most usual call is CaaW!-CaaW!-CaaW!. Plumage is all black, with iridescent feathers. It looks much like other all-black corvids. They can be distinguished from the common raven (C. corax) because American crows are smaller; from the fish crow (C. ossifragus) because American crows do not hunch and fluff their throat feathers when they call; and from the carrion crow (C. corone) by size, as the carrion crow is larger and of a stockier build. They are very intelligent, and adaptable to human environments.

American crows are common, widespread, and susceptible to the West Nile virus, making them useful as a bioindicator to track the virus's spread. Direct transmission of the virus from crows to humans is impossible. They are considered an agricultural pest, and are subject to hunting and management.

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Corneille d'Amérique

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Corvus brachyrhynchos

La Corneille d'Amérique (Corvus brachyrhynchos) est une espèce de grands passereaux de la famille des Corvidae.

Cette corneille a un plumage iridescent complètement noir, et ressemble à la Corneille noire, qui vit en Europe, au Grand Corbeau et à la Corneille d'Alaska. Elle se distingue de ces autres espèces par la taille, la niche écologique, la voix ou la répartition géographique. La Corneille d'Amérique est protégée par la Loi sur la convention concernant les oiseaux migrateurs. C'est une espèce grégaire.

Taxonomie

La Corneille d'Amérique a été décrite par Christian Ludwig Brehm en 1822. Le nom de l'espèce brachyrhynchos « à bec court » est dérivé du grec brachy-/βραχυ- « court » et rhynchos/ρυνχος « bec »[1]. Plusieurs espèces ont pour nom brachyrhynchus, une seule brachyrhynchos.

La Corneille d'Alaska (Corvus caurinus) est proche parente de la Corneille d'Amérique. Il est difficile de les distinguer là où leurs aires de répartition se recoupent. Cependant, la voix diffère de façon caractéristique entre les deux espèces[2], sauf dans le nord-ouest de l'aire de répartition de la Corneille d'Amérique où celle-ci présente une voix rauque indistinguable de celle de la Corneille d'Alaska[3].

Liste des sous-espèces

D'après la classification de référence (version 5.2, 2015) du Congrès ornithologique international, cette espèce est constituée des quatre sous-espèces suivantes (ordre phylogénique) :

  • Corvus brachyrhynchos hesperis Ridgway, 1887 ; sous-espèce plutôt petite (39 à 44 cm de longueur ; 278 à 325 mm d'aile pliée ; 159 à 190 mm pour la queue ; 46 à 50 mm pour le bec et 53 à 59 mm pour le tarse) avec une voix un peu plus grave occupant l'ouest des États-Unis ;
  • Corvus brachyrhynchos hargravei A.R. Phillips, 1942 ;
  • Corvus brachyrhynchos brachyrhynchos Brehm, 1822 ; sous-espèce plutôt grande (39 à 49 cm de longueur ; 282 à 333 mm d'aile pliée ; 155 à 198 mm pour la queue ; 46 à 53 mm pour le bec et 55 à 65 mm pour le tarse) occupant le nord et le centre de l'aire de répartition de l'espèce ;
  • Corvus brachyrhynchos pascuus Coues, 1899 ; sous-espèce de taille moyenne (43 à 48 cm de longueur ; 280 à 324 mm d'aile pliée ; 153 à 185 mm pour la queue ; 48 à 55 mm pour le bec et 59 à 66 mm pour le tarse) présente en Floride.

Description

 src=
Corneille d'Amérique lançant son appel

Le plumage, les pattes et le bec sont noirs. En Amérique du Nord, plusieurs formes régionales sont reconnues avec des différences au niveau de la taille et des proportions du bec. Les individus sont généralement plus petits dans le sud-est et l'ouest du continent. Pour les distinguer en vol, on peut observer la forme de la queue ; la base de la queue de la corneille est plate ou légèrement arrondie, tandis que celle du corbeau termine en pointe ou avec un arrondi prononcé[4]. Les corneilles mesurent entre 39 et 53 centimètres, et pèsent environ 450 grammes (458 g pour le mâle et 438 g pour la femelle). Les deux sexes sont semblables. Le croassement est rauque et discordant. Les individus peuvent également produire une grande variété de sons et imiter les cris d'autres oiseaux.

Répartition et habitat

 src=
Carte de répartition de l'espèce.

Au Canada, la Corneille d'Amérique se retrouve de Terre-Neuve jusqu'en Colombie-Britannique, tout en étant absente de la côte du Pacifique, où elle est remplacée par la Corneille d'Alaska. Elle niche également à Saint-Pierre-et-Miquelon, partout aux États-Unis sauf dans les zones désertiques du sud-ouest et au nord du Mexique.

Elle exploite de nombreux types d'habitats, dont les milieux ouverts et les milieux boisés, les champs, les pâturages, les vergers, les marais, les tourbières, les rivages, les cimetières et les milieux urbains. Les populations les plus nordiques migrent sur de plus ou moins longues distances vers le sud en hiver. Après la saison de reproduction, les groupes familiaux se rassemblent en bandes importantes (pouvant comporter des dizaines de milliers d'individus) et se réunissent en dortoirs pour la nuit.

La corneille d'Amérique a été enregistrée dans les Bermudes à partir de 1876[5].

Comportement

Alimentation

La Corneille d'Amérique est omnivore. Elle consomme des insectes, des crustacés, des mollusques et d'autres invertébrés, des amphibiens, des reptiles, des poissons, des œufs et des oisillons, des petits mammifères, des charognes, des déchets alimentaires, des fruits et des graines, et même, en bord de mer, des coquillages et des oursins. Elle possède une cavité antélinguale qui lui permet d'emmagasiner et de transporter de la nourriture. Elle se constitue parfois des réserves dans des caches. Elle régurgite sous forme de boulettes les matières non digérées tels les poils et les os. La Corneille d'Amérique est l'une des rares espèces d'oiseaux capables de modifier et d'utiliser des outils afin d'obtenir de la nourriture[6].

Reproduction

 src=
Œuf de Corvus brachyrhynchos dans la collection du Children's Museum of Indianapolis

La Corneille d'Amérique est monogame et n'est pas sexuellement mature avant l'âge de deux ans. La plupart des individus ne se reproduisent qu'à l'âge de quatre ou cinq ans. De ce fait, les familles sont composées d'un couple et de leur progéniture (jusqu'à 15 individus) provenant des saisons de reproduction antérieures. Ces jeunes individus aident le couple reproducteur à défendre le territoire, à construire le nid et à élever les oisillons.

Le nid est fait de brindilles et est tapissé d'herbes, d'aiguilles de pin, de mousses, de feuilles, de poils et de plumes. Il est presque toujours placé dans des arbres ou de grands buissons. Plus rarement, il est placé au sol. La femelle pond de 3 à 6 œufs qu'elle incube 18 jours. Les jeunes quittent le nid à l'âge de 35 jours.

Conservation

Dans plusieurs régions, les chasseurs et les agriculteurs ont tenté d'éliminer les corneilles. Dans les dortoirs, des milliers d'individus ont été abattus, empoisonnés ou même dynamités. Cependant, ces actes ont provoqué de violentes critiques et protestations tout en étant inefficaces; la Corneille d'Amérique reste commune. Birdlife International estime qu'il existe environ 31 millions de Corneille d'Amérique en 2004[7] et le statut de cette espèce est donc de préoccupation mineure.

Annexes

Références taxonomiques

Notes et références

  1. (en) Liddell et Scott, Greek-English Lexicon, Abridged Edition, Oxford, UK, Oxford University Press, 1980, 804 p. (ISBN 978-0-19-910207-5, LCCN )
  2. (en) Whatbird.com, « American Crow » (consulté le 18 octobre 2007)
  3. Madge S. & Burn H. (1996) Corbeaux et Geais. Guide des Corbeaux, Geais et Pies du monde entier. Vigot, Paris, 184 p.
  4. « Refuge Pageau »
  5. (en) John L. Long, Oiseaux réintroduits du Monde : L'histoire dans le monde entier, répartition et influence des oiseaux introduits dans un nouvel environnement, Terrey Hills, Sydney, Reed, 1981 (ISBN 0-589-50260-3), p. 354
  6. Caffrey, C. (2000) Tool Modification and Use by an American Crow. The Wilson Bulletin: Vol. 112, No. 2 pp. 283–284.
  7. (UICN, 2004)

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Corneille d'Amérique: Brief Summary

provided by wikipedia FR

Corvus brachyrhynchos

La Corneille d'Amérique (Corvus brachyrhynchos) est une espèce de grands passereaux de la famille des Corvidae.

Cette corneille a un plumage iridescent complètement noir, et ressemble à la Corneille noire, qui vit en Europe, au Grand Corbeau et à la Corneille d'Alaska. Elle se distingue de ces autres espèces par la taille, la niche écologique, la voix ou la répartition géographique. La Corneille d'Amérique est protégée par la Loi sur la convention concernant les oiseaux migrateurs. C'est une espèce grégaire.

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