American Crow
Encyclopedia
The American Crow is a large passerine
bird species
of the family
Corvidae
. It is a common bird found throughout much of North America
. In the interior of the continent south of the Arctic
, it is simply called "the crow", as no other such birds occur there on any regular basis.
It is one of several species of corvid that are entirely black, though it can be distinguished from the other two such birds in its range—from the Common Raven
(C. corax) by size and behavior and from the Fish Crow
(C. ossifragus) by call (but see below). It is also distinguished from the Raven by its smaller, more curved bill than the parallel bill of the raven, and its squared tail.
American Crows are common, widespread and adaptable, but they are highly susceptible to the West Nile Virus
. They are monitored as a bioindicator
. Direct transmission of the virus from American Crows to humans is not recorded to date, and in any case not considered likely.
Although both the American crow and the Hooded crow
strongly resemble in size, structure and behavior, their calls are different. The American crow nevertheless occupies the same role the hooded crow does in Eurasia
.
in 1822. Its scientific name means literally "short-billed crow", from Ancient Greek
brachy- (βραχυ-) "short-" and rhynchos (ρυνχος) "billed".
The Northwestern Crow
(C. caurinus) is very closely related to the American Crow. Its ancestors became separated by Ice Age
glaciation west of the Rocky Mountains
. It is endemic to Pacific temperate rain forests
where it all but replaces the American Crow. Only in the Seattle region do they co-occur to any extent. In form the two species are much alike. There is a marked difference in voice.
in size across North America
. Birds are smallest in the far west and on the south coast.
The American Crow is a distinctive bird with iridescent
black feathers all over. Its legs, feet and bill are also black. They are 40–50 cm (16–20 in) in length, of which the tail makes up about 40%. Each wing is around 27–34 cm (11–14 in) long. The bill length is on average 5 cm (2 in), varying strongly according to location. Males tend to be larger than females.
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.
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 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 Raven
s (C. corax) can be distinguished by their almost lozenge
-shaped tail, their larger-looking heads and of course their strongly solitary habits. They also fluff their throat feathers when calling like Fish Crows, only more so.
Most wild American Crows live for about 7–8 years. Captive birds are known to have lived up to 30 years.
to the Atlantic Ocean
in Canada
, on the French
islands of Saint-Pierre and Miquelon
, south through the United States
, and into northern Mexico
. Virtually all types of country from wilderness, farmland, parks, open woodland to towns and major cities are inhabited; it is absent only from Pacific temperate rain forests
and tundra
habitat where it is replaced by the raven
. This crow is a permanent resident in most of the USA, but most Canadian birds migrate
some distances southward in winter. Outside of the nesting season
these birds often gather in large communal roosts at night.
The American Crow was recorded in Bermuda
from 1876 onwards.
. It will feed on invertebrate
s of all types, carrion
, scraps of human food, seed
s, eggs
and nestlings, stranded fish
on the shore and various grain
s. American Crows are active hunters and will prey on mice
, frog
s, and other small animals. In winter and autumn, the diet of American Crows is more dependent on nuts
and acorns. Occasionally, they will visit bird feeder
s. The American Crow is one of only a few species of bird that has been observed modifying and using tools
to obtain food.
Like most crows, they will scavenge
at landfill
s, 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.
cooperative breeding
birds. Mated pairs form large families of up to 15 individuals from several breeding season
s that remain together for many years. 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. Most do not leave the nest to breed for four to five years.
The nesting season starts early, with some birds incubating eggs by early April. American Crows build bulky stick nest
s, 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 oak
s are most often used. Three to six eggs are laid and incubated for 18 days. The young are usually fledge
d by about 35 days after hatching.
infection. This was originally a mosquito
-borne Africa
n 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; 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. 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.
American Crows are protected internationally by the Migratory Bird Treaty Act of 1918
. Despite attempts by humans in some areas to drive away or eliminate these birds, they remain widespread and very common. The number of individual American Crows is estimated by Birdlife International
to be around 31,000,000. The large population, as well as its vast range, are the reasons why the American Crow is considered to be of least concern
, meaning that the species is not threatened.
Passerine
A passerine is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders: with over 5,000 identified species, it has roughly...
bird species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Corvidae
Corvidae
Corvidae is a cosmopolitan family of oscine passerine birds that contains the crows, ravens, rooks, jackdaws, jays, magpies, treepies, choughs and nutcrackers. The common English names used are corvids or the crow family , and there are over 120 species...
. It is a common bird found throughout much of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. In the interior of the continent south of the Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
, it is simply called "the crow", as no other such birds occur there on any regular basis.
It is one of several species of corvid that are entirely black, though it can be distinguished from the other two such birds in its range—from the Common Raven
Common Raven
The Common Raven , also known as the Northern Raven, is a large, all-black passerine bird. Found across the northern hemisphere, it is the most widely distributed of all corvids...
(C. corax) by size and behavior and from the Fish Crow
Fish Crow
The Fish Crow is a species of crow that is associated with wetland habitats in the eastern and southeastern United States.-Taxonomy:The Fish Crow was first described by Alexander Wilson in 1812...
(C. ossifragus) by call (but see below). It is also distinguished from the Raven by its smaller, more curved bill than the parallel bill of the raven, and its squared tail.
American Crows are common, widespread and adaptable, but they are highly susceptible to the West Nile Virus
West Nile virus
West Nile virus is a virus of the family Flaviviridae. Part of the Japanese encephalitis antigenic complex of viruses, it is found in both tropical and temperate regions. It mainly infects birds, but is known to infect humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, domestic...
. They are monitored as a bioindicator
Bioindicator
Biological indicators are species used to monitor the health of an environment or ecosystem. They are any biological species or group of species whose function, population, or status can be used to determine ecosystem or environmental integrity. An example of such a group are the copepods and other...
. Direct transmission of the virus from American Crows to humans is not recorded to date, and in any case not considered likely.
Although both the American crow and the Hooded crow
Hooded Crow
The Hooded Crow is a Eurasian bird species in the crow genus. Widely distributed, it is also known locally as Scotch Crow, Danish Crow, and Corbie or Grey Crow in Ireland, which is what its Welsh name, Brân Lwyd, translates as...
strongly resemble in size, structure and behavior, their calls are different. The American crow nevertheless occupies the same role the hooded crow does in Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
.
Taxonomy
The American Crow was described by Christian Ludwig BrehmChristian Ludwig Brehm
Christian Ludwig Brehm was a German pastor and ornithologist. He was the father of Alfred Brehm.Brehm was born near Gotha, and studied at the University of Jena. In 1813 he became the minister at Renthendorf, a village sixty miles south of Leipzig, where he remained until his death...
in 1822. Its scientific name means literally "short-billed crow", from Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
brachy- (βραχυ-) "short-" and rhynchos (ρυνχος) "billed".
The Northwestern Crow
Northwestern Crow
The Northwestern Crow is an all-black passerine bird of the crow genus native to the northwest of North America. It is very similar to the more western forms of the widespread American Crow , but it averages slightly smaller with proportionately smaller feet and a slightly more slender bill...
(C. caurinus) is very closely related to the American Crow. Its ancestors became separated by Ice Age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
glaciation west of the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
. It is endemic to Pacific temperate rain forests
Pacific temperate rain forests
The Pacific temperate rain forests ecoregion of North America is the largest temperate rain forest ecoregion on the planet as defined by the World Wildlife Fund...
where it all but replaces the American Crow. Only in the Seattle region do they co-occur to any extent. In form the two species are much alike. There is a marked difference in voice.
Subspecies
Four subspecies are recognized. They differ in bill proportion and form a rough NE-SW clinalCline (population genetics)
In biology, an ecocline or simply cline describes an ecotone in which a series of biocommunities display continuous gradient...
in size across North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Birds are smallest in the far west and on the south coast.
- Corvus brachyrhynchos brachyrhynchos – Eastern Crow: northeastern United StatesNortheastern United StatesThe Northeastern United States is a region of the United States as defined by the United States Census Bureau.-Composition:The region comprises nine states: the New England states of Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont; and the Mid-Atlantic states of New...
, eastern CanadaCanadaCanada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
and surroundings. Largest subspecies. - Corvus brachyrhynchos hesperis – Western Crow: Western North America except arcticArcticThe Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
north, Pacific NorthwestPacific NorthwestThe Pacific Northwest is a region in northwestern North America, bounded by the Pacific Ocean to the west and, loosely, by the Rocky Mountains on the east. Definitions of the region vary and there is no commonly agreed upon boundary, even among Pacific Northwesterners. A common concept of the...
and extreme south. Smaller overall with a proportionally more slender bill and low-pitched voice. - Corvus brachyrhynchos pascuus – Florida Crow: FloridaFloridaFlorida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
. Mid-sized, short-winged but decidedly long bill and legs. - Corvus brachyrhynchos paulus – Southern Crow: southern United StatesSouthern United StatesThe Southern United States—commonly referred to as the American South, Dixie, or simply the South—constitutes a large distinctive area in the southeastern and south-central United States...
. Smaller overall, bill also small.
Description
Iridescence
Iridescence is generally known as the property of certain surfaces which appear to change color as the angle of view or the angle of illumination changes...
black feathers all over. Its legs, feet and bill are also black. They are 40–50 cm (16–20 in) in length, of which the tail makes up about 40%. Each wing is around 27–34 cm (11–14 in) long. The bill length is on average 5 cm (2 in), varying strongly according to location. Males tend to be larger than females.
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.
Visual differentiation from the Fish Crow
Fish Crow
The Fish Crow is a species of crow that is associated with wetland habitats in the eastern and southeastern United States.-Taxonomy:The Fish Crow was first described by Alexander Wilson in 1812...
(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 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 Raven
Common Raven
The Common Raven , also known as the Northern Raven, is a large, all-black passerine bird. Found across the northern hemisphere, it is the most widely distributed of all corvids...
s (C. corax) can be distinguished by their almost lozenge
Lozenge
A lozenge , often referred to as a diamond, is a form of rhombus. The definition of lozenge is not strictly fixed, and it is sometimes used simply as a synonym for rhombus. Most often, though, lozenge refers to a thin rhombus—a rhombus with acute angles of 45°...
-shaped tail, their larger-looking heads and of course their strongly solitary habits. They also fluff their throat feathers when calling like Fish Crows, only more so.
Most wild American Crows live for about 7–8 years. Captive birds are known to have lived up to 30 years.
Distribution and habitat
The range of the American Crow extends from the Pacific OceanPacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
to the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, on the French
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
islands of Saint-Pierre and Miquelon
Saint-Pierre and Miquelon
Saint Pierre and Miquelon is a self-governing territorial overseas collectivity of France. It is the only remnant of the former colonial empire of New France that remains under French control....
, south through the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, and into northern Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
. Virtually all types of country from wilderness, farmland, parks, open woodland to towns and major cities are inhabited; it is absent only from Pacific temperate rain forests
Pacific temperate rain forests
The Pacific temperate rain forests ecoregion of North America is the largest temperate rain forest ecoregion on the planet as defined by the World Wildlife Fund...
and tundra
Tundra
In physical geography, tundra is a biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word tūndâr "uplands," "treeless mountain tract." There are three types of tundra: Arctic tundra, alpine...
habitat where it is replaced by the raven
Common Raven
The Common Raven , also known as the Northern Raven, is a large, all-black passerine bird. Found across the northern hemisphere, it is the most widely distributed of all corvids...
. This crow is a permanent resident in most of the USA, but most Canadian birds migrate
Bird migration
Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...
some distances southward in winter. Outside of the nesting season
Nesting season
The nesting season is the time of year during which birds and some other animals, particularly some reptiles, build nests, lay eggs in them, and in most cases bring up their young. It is usually in the spring....
these birds often gather in large communal roosts at night.
The American Crow was recorded in Bermuda
Flora and fauna in Bermuda
The flora and fauna of Bermuda forms part of a unique ecosystem thanks to Bermuda's isolation from the mainland of North America. There are a wide range of endemic species and the islands form a distinct ecoregion, the Bermuda subtropical conifer forests....
from 1876 onwards.
Diet
The American Crow is omnivorousOmnivore
Omnivores are species that eat both plants and animals as their primary food source...
. It will feed on invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s of all types, carrion
Carrion
Carrion refers to the carcass of a dead animal. Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters include vultures, hawks, eagles, hyenas, Virginia Opossum, Tasmanian Devils, coyotes, Komodo dragons, and burying beetles...
, scraps of human food, seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s, eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
and nestlings, stranded fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
on the shore and various grain
GRAIN
GRAIN is a small international non-profit organisation that works to support small farmers and social movements in their struggles for community-controlled and biodiversity-based food systems. Our support takes the form of independent research and analysis, networking at local, regional and...
s. American Crows are active hunters and will prey on mice
Mouse
A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...
, frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
s, and other small animals. In winter and autumn, the diet of American Crows is more dependent on nuts
Nut (fruit)
A nut is a hard-shelled fruit of some plants having an indehiscent seed. While a wide variety of dried seeds and fruits are called nuts in English, only a certain number of them are considered by biologists to be true nuts...
and acorns. Occasionally, they will visit bird feeder
Bird feeder
A birdfeeder, bird feeder, bird table, or tray feeder are devices placed outdoors to supply bird food to birds...
s. The American Crow is one of only a few species of bird that has been observed modifying and using tools
Tool use by animals
Tools are used by some animals, particularly primates, to perform simple tasks such as the acquisition of food, or grooming. Originally thought to be a skill only possessed by humans, tool use requires some level of intelligence. Primates have been observed exploiting sticks and stones to...
to obtain food.
Like most crows, they will scavenge
Scavenger
Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
at landfill
Landfill
A landfill site , is a site for the disposal of waste materials by burial and is the oldest form of waste treatment...
s, scattering garbage in the process. Where available, corn
Maize
Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...
, wheat
Wheat
Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
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
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
pests.
Reproduction
American Crows are monogamousMonogamy
Monogamy /Gr. μονός+γάμος - one+marriage/ a form of marriage in which an individual has only one spouse at any one time. In current usage monogamy often refers to having one sexual partner irrespective of marriage or reproduction...
cooperative breeding
Cooperative breeding
Cooperative breeding is a social system in which individuals contribute care to offspring that are not their own at the expense of their own reproduction . When reproduction is monopolized by one or few of the adult group members and most adults do not reproduce, but help rear the breeder’s...
birds. Mated pairs form large families of up to 15 individuals from several breeding season
Breeding season
The breeding season is the most suitable season, usually with favourable conditions and abundant food and water, for breeding among some wild animals and birds . Species with a breeding season have naturally evolved to have sexual intercourse during a certain time of year in order to achieve the...
s that remain together for many years. Offspring from a previous nesting season will usually remain with the family to assist in rearing
Helpers at the nest
Helpers at the nest is a term used in behavioural ecology and evolutionary biology to describe a social structure in which juveniles and sexually mature adolescents of either one or both sexes, remain in association with their parents and help them raise subsequent broods or litters, instead of...
new nestlings. American Crows do not reach breeding age for at least two years. Most do not leave the nest to breed for four to five years.
The nesting season starts early, with some birds incubating eggs by early April. American Crows build bulky stick nest
Bird nest
A bird nest is the spot in which a bird lays and incubates its eggs and raises its young. Although the term popularly refers to a specific structure made by the bird itself—such as the grassy cup nest of the American Robin or Eurasian Blackbird, or the elaborately woven hanging nest of the...
s, 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 oak
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
s are most often used. Three to six eggs are laid and incubated for 18 days. The young are usually fledge
Fledge
Fledge is the stage in a young bird's life when the feathers and wing muscles are sufficiently developed for flight. It also describes the act of a chick's parents raising it to a fully grown state...
d by about 35 days after hatching.
West Nile Virus
American Crows succumb easily to West Nile virusWest Nile virus
West Nile virus is a virus of the family Flaviviridae. Part of the Japanese encephalitis antigenic complex of viruses, it is found in both tropical and temperate regions. It mainly infects birds, but is known to infect humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, domestic...
infection. This was originally a mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
-borne Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
n virus causing encephalitis
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
in humans and livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...
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; 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. Because of this, American Crows are a sentinel species
Bioindicator
Biological indicators are species used to monitor the health of an environment or ecosystem. They are any biological species or group of species whose function, population, or status can be used to determine ecosystem or environmental integrity. An example of such a group are the copepods and other...
indicating the presence of West Nile virus in an area. Crows cannot transmit the virus to humans directly.
Status and conservation
Crows have been killed in large numbers by humans, both for recreation and as part of organized campaigns of extermination.American Crows are protected internationally by the Migratory Bird Treaty Act of 1918
Migratory Bird Treaty Act of 1918
The Migratory Bird Treaty Act of 1918 , codified at , is a United States federal law, at first enacted in 1916 in order to implement the convention for the protection of migratory birds between the United States and Great Britain...
. Despite attempts by humans in some areas to drive away or eliminate these birds, they remain widespread and very common. The number of individual American Crows is estimated by Birdlife International
BirdLife International
BirdLife International is a global Partnership of conservation organisations that strives to conserve birds, their habitats and global biodiversity, working with people towards sustainability in the use of natural resources...
to be around 31,000,000. The large population, as well as its vast range, are the reasons why the American Crow is considered to be of least concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
, meaning that the species is not threatened.
Images
- American Crow Facts and Photos
- Skull of American Crow
- Pictures of American Crow on Birds of the World at Flickr
- American Crow videos, photos & sounds on the Internet Bird Collection
