Northwestern crows are mid-sized birds, 41.9 to 44.5 cm long and weighing 340 to 440 g. They have a wingspan of about 99 cm and their feathers are iridescent black with bluish-violet on their head, neck, back, wings, and tail. Their eyes are a smokey brownish-grey color, and their bills are glossy and stout though smaller and less powerful than those of common ravens (Corvus corax). They also have bristlelike feathers covering the nares. has thick, black legs with large scales on the front side only. When at rest, the tips of their folded wings do not reach the tip of the tail, which has slightly rounded ends. The sexes look alike, though the male is slightly larger than the female. ("Bird Identification Page", 2001; Verbeek and Butler, 1999)
Immature (Verbeek and Butler, 1999)between 3 to 15 months are also black, but have less iridescence than adults. Their back, wing and tail feathers fade gradually from black to brown. Juveniles from 1 to 3 months have looser, fluffier feathers than adult or immature and their feathers are a dull black. They have blue eyes.
Corvus brachyrhynchos) because it is about 10% smaller, with smaller feet. It is also smaller than common ravens (C. corax), and while C. corax has a wedge-shaped tail, the tail of is squarish. Corvus corax also has shaggy throat-feathers which lacks. (Verbeek and Butler, 1999)can be distinguished from American crows (
It is not known when northwestern crows ( (Verbeek and Butler, 1999)) form breeding pairs, but it is most likely sometime in their second year, prior to the breeding season. If a courtship display exists, it is very subtle and has not been observed. However, prior to copulation, the male droops, spreads his wings and tail, points his bill down and quivers his wings and tail while exposing nictitating membranes (a transparent inner eyelid in birds). The female has a similar display, but she crouches and quivers her tail rapidly.
Young (Verbeek and Butler, 1999)probably reach sexual maturity between 15 and 20 months. They copulate and begin building nests from early February through late March. Northwestern crows breed once yearly, but they will renest if disturbed early in the season. The female selects a place to build the nest, normally in or under trees, shrubs, blackberry tangles, or tall grass. Nest-building occurs only during daylight hours and in good weather. Nests are built with branches broken off of trees, grass and moss as well as other objects and soil. line their nests with moss, gull and crow feathers and sheep's wool, among other things.
A female (Verbeek and Butler, 1999)typically lays 3 to 6 eggs per breeding season, laying one egg a day, almost always before 8:00 AM. Eggs are pale bluish with darker brown spots and are subelliptical to oval. They have a smooth, slightly glossy surface and are about 40 mm long and 28 mm wide.
Incubation most likely begins on the second day, and is performed by the female only. The incubation period is about 18 days; during this time the male feeds the female, most often at a small distance from the nest. After the eggs have hatched, female (Verbeek and Butler, 1999)begin feeding the hatchlings.
Adult (Verbeek and Butler, 1999)build nests for their young, then lay eggs. The female broods the altricial young for about 18 days before devoting all of her time to gathering food and feeding them. The male, and sometimes a helper, will bring food from the time they hatch, until about 77 days after hatching. Young leave the nest at about 31 days but still rely on their parents for food as they can only make short flights. They begin to feed on their own starting around 55 days and parents generally stop feeding them at 77 days. Parent birds protect their offspring throughout this time. Immature associate with roosting groups of adults and feed near them for the first year or two, probably to pick up their leftovers and learn the intricacies of feeding.
Northwestern crows walk, hop and fly. They fly with a steady, regular wing-beat and make use of strong winds to glide along cliffs. They fly at about 30 km/h and have a wing-beat that is faster than that of American crows (C. brachyrhynchos). They are very maneuverable in flight. They have also been seen playing games, flying high into the air in order to drop a stick or stone from their claws or beak then rush back down to grasp it again. (Verbeek and Butler, 1999)
During the mating season, (Verbeek and Butler, 1999)pairs defend a territory of about 0.48 ha against all other adults, all unrelated fledglings and most or all related fledglings by calling, chasing, flying and displaying. At times they will share a larger range with a loose group of other nesting pairs. Breeding pairs tend to return to the same territory each breeding season and use the same roosting sites for the rest of the year. The size of home ranges is largely unknown and varies based on availability of food.
Northwestern crows (Verbeek and Butler, 1999)communicate mainly with calls. They have a variety of calls with meanings that range from threatening territorial defense calls to begging or feeding calls. Males have a specific call that they use to signal to brooding females that they are bringing food and she should come get some. They are very vocal in roosting groups and use warning calls and mob calls that will quickly bring the whole community together in order to scare off a would-be predator. They also engage in some visual displays, mostly to declare dominance, territory rights and to signal willingness to mate.
Northwestern crows are omnivorous scavengers. They can and will eat almost anything they can find. Their diet ranges from small invertebrates, to human garbage, to fruit, depending on what is available. Along coasts they feed mainly on clams (Venerupis philippinarum and Protothaca staminea) crustaceans and sand dollars (Dendraster excentricus). The crows pick these animals up, fly high into the air and drop them on rocks in order to break them open. They have also been known to eat sea urchins (Strongylocentrotus purpuratus) off of rocks and to steal eggs and nestlings from peregrine falcons (Falco peregrinus) and cormorants (family Phalacrocoracidae), among others. Blackberries are an important part of their diet, as are many forms of carrion such as fish, dead seals, dead birds, roadkill and dead insects from the grills of cars. (Verbeek and Butler, 1999)
They can be seen walking along the shore, digging through the sand for clams, stabbing the ground in search of insects and wading in shallow tide pools. They have also been known to root through garbage cans and landfills. (Verbeek and Butler, 1999)
As a social animal, Circus cyaneus), hawks (Accipiter striatus and Buteo jamaicensis) , owls (Tyto alba, Asio flammeus and Asio otus), gray squirrels (Sciurus carolinensis), domestic cats (Felis silvestris), dogs (Canis lupus familiaris) and people. They also chase young birds, juvenile squirrels and raccoons (Procyon lotor). Many predators, such as garter snakes (genus Thamnophis), other birds, and possibly gray squirrels, are primarily a threat to nestlings and fledglings, these animals are attacked, chased or mobbed by the parents.relies greatly on roosting partners for protection. They alert one another to predators with calls and then mob the potential predator and create a deafening noise by calling together. They tend to perch above predators and call down at them. They have been seen mobbing northern harriers (
Predators of Circus cyaneus), sharp-shinned hawks (Accipiter striatus), red-tailed hawks (Buteo jamaicensis), owls (Tyto alba, Asio flammeus and Asio otus), gray squirrels (Sciurus carolinensis), domestic cats (Felis silvestris), dogs (Canis lupus familiaris), raccoons (Procyon lotor), northern goshawks (Accipiter gentilis), garter snakes (genus Thamnophis), Cooper's hawks (Accipiter cooperii) and bald eagles (Haliaeetus leucocephalus). (Robinette and James, 2001; Verbeek and Butler, 1999)include: northern harriers (
Blackberries are also an important food for (Verbeek and Butler, 1999)and it acts as a disperser of blackberry seeds.
Northwestern crows have been known to feed on crops. (Verbeek and Butler, 1999)
This species is protected by the US Migratory Bird Treaty Act. Overall, ( (Verbeek and Butler, 1999)) has benefited from human contact because humans clear out deep forests creating more of the open, forest fringe which these crows thrive in.
Very little research has been done on (Verbeek and Butler, 1999), it is a relatively restricted species that occupies an unfriendly environment so it does not come into contact with humans very often. It also seems to have a fairly stable population. The number of individuals in a given area is based largely upon food availability and how many birds the area can support.
Alaine Camfield (editor), Animal Diversity Web.
Brynne McBryde (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
uses sound to communicate
living in landscapes dominated by human agriculture.
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
helps break down and decompose dead plants and/or animals
flesh of dead animals.
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
helpers provide assistance in raising young that are not their own
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
Having one mate at a time.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats all kinds of things, including plants and animals
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
specialized for leaping or bounding locomotion; jumps or hops.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
places a food item in a special place to be eaten later. Also called "hoarding"
living in residential areas on the outskirts of large cities or towns.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
living in cities and large towns, landscapes dominated by human structures and activity.
uses sight to communicate
Canadian Cooperative Wildlife Health Center. 2001. "Bird Identification Page" (On-line). West Nile Maps. Accessed April 02, 2004 at http://wildlife.usask.ca/WestNileAlertHTML/WestNileAlertBirdPage.htm.
James, P., N. Verbeek. 1983. The food storage behavior of the northwestern crow Corvus caurinus. Behaviour, 85 (3-4): 276-291.
Robinette, R., C. James. 2001. Social and ecological factors influencing vigilance by northwestern crows, Corvus caurinus. Animal Behaviour, 62 (3): 447-452.
Robinette, R., C. James. 1997. The significance of fishing by Northwestern Crows. The Wilson Bulletin, 109(4): 748-749.
Verbeek, N., R. Butler. 1999. Northwestern Crow (Corvus caurinus). The Birds of North America, 407: 1-23.