Corvus caurinus
north-western crow
(Also: northwestern crow)

Corvus caurinus lives only along the coast of the northeastern Pacific Ocean between southern Alaska and the northern tip of Washington. (Verbeek and Butler, 1999)

Corvus caurinus lives mainly in coastal regions near intertidal zones, but can be found along large rivers as far as 120 km inland. They are typically near, but not necessarily in, forested regions and will pull back into the forest edge during harsh weather conditions in winter. Northwestern crows are also likely to live near seabird colonies and refuse dumps. They have also been found living in river deltas, coastal bays, coastal villages, towns and cities, as well as on farmland. They can be found at elevations up to 1700 m. (Verbeek and Butler, 1999)

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. Corvus caurinus 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. (Canadian Cooperative Wildlife Health Center, 2001; Verbeek and Butler, 1999)

Immature C. caurinus 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 C. caurinus and their feathers are a dull black. They have blue eyes. (Verbeek and Butler, 1999)

Corvus caurinus can be distinguished from American crows (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 C. caurinus is squarish. Corvus corax also has shaggy throat-feathers which C. caurinus lacks. (Verbeek and Butler, 1999)

Corvus caurinus typically lives about 12 years in the wild, if it fledges. The longest known lifespan is 17 years. About 10% of eggs fail to hatch and many hatchlings either starve or are killed before they leave the nest. Some fledglings in coastal territories fall into the ocean and drown or are killed by neighboring colonies of gulls. Disease accounts for few deaths in C. caurinus populations. The main known cause of death is recreational shooting in British Columbia, but food availability is probably a large factor in determining population sizes. Corvus caurinus are not kept in captivity. (Verbeek and Butler, 1999)

Corvus caurinus spends the breeding season in territorial pairs. After the fledgling period they gradually decrease territorial behavior and eventually the entire family goes to live in a large roosting community. Yearlings and non-mating adults remain in the roosting community year-round. Within a roosting community, certain birds will act as sentries, keeping an eye out for available food, possible thieves and predators. They communicate with the rest of the flock through calls. Immature birds and fledglings have been known to play with one another while in flight. Corvus caurinus does not have a set hierarchy within roosting groups, but males are generally dominant over females, and females are dominant over yearlings and fledglings. When there is a breeding helper, the helper is subordinate to both adults, but dominant over any other adults trespassing on their territory. (Robinette and James, 2001; Verbeek and Butler, 1999)

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)

Home Range

During the mating season, C. caurinus 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. (Verbeek and Butler, 1999)

Northwestern crows C. caurinus 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. (Verbeek and Butler, 1999)

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 japonica 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)

Corvus caurinus will also cache food in the morning and evenings. Saved items include clams, cormorant eggs, crabs and fish. Cached food is typically retrieved within 24 hours. They also transport cached food for young and incubating females. Food caching seems to take place mainly at the beginning of the breeding season during high tide. It is believed that one main function of caching food is that it guarantees food for the female and nestlings at a time when food could become scarce. Corvus caurinus caches food in vegetation and along rocks. They most often attempt to bury the food and seem to memorize its location in order to find it again. (James and Verbeek, 1983; Verbeek and Butler, 1999)

As a social animal, C. caurinus 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 (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.

Predators of C. caurinus include: northern harriers (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)

Corvus caurinus feeds on many different organisms, both living and dead. It eats many of the species that inhabit northern tide pools and cleans up carrion and refuse in all of its habitats. It is prey to some large sea birds and some smaller vertebrates feed on C. caurinus nestlings. Nestlings and adults serve as hosts to louse flies, bird blow fly larvae (Protocaliphora braueri), fleas Ceratophyllus niger, and feather louse Myrsidea interrupta. (Robinette and James, 2001; Verbeek and Butler, 1999)

Blackberries are also an important food for C. caurinus and it acts as a disperser of blackberry seeds. (Verbeek and Butler, 1999)

Northwestern crows have been known to feed on crops. (Verbeek and Butler, 1999)

Corvus caurinus provides an important cleaning service to humans. It keeps shorelines and riversides free of refuse and carrion. It also plays an important role in keeping tide pool ecosystems in check. Studies show that predatory sea birds, including C. caurinus are a significant factor in controlling sea urchin populations. Northwestern crows hold down populations of clams and crabs, preventing overpopulation and maintaining biodiversity in the ocean and intertidal zones. (Robinette and James, 1997; Verbeek and Butler, 1999)

This species is protected by the US Migratory Bird Treaty Act. Overall, (C. caurinus) has benefited from human contact because humans clear out deep forests creating more of the open, forest fringe which these crows thrive in. (Verbeek and Butler, 1999)

Very little research has been done on C. caurinus, 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. (Verbeek and Butler, 1999)