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Northwestern Crow Life History

Habitat

Habitat Open Woodlands

Northwestern Crows are mostly permanent residents in coastal areas near the intertidal zone, often found by bays or rivermouths, along beaches, on islands, or at landfills. They forage in tidepools, on mudflats, in seabird colonies, as well as in many human-modified environments (residential and agricultural), where they are opportunists in their feeding, much like American Crows. Although they inhabit forest edges, they are unreported in heavily forested areas away from the coast. Birds that nest on some offshore islands withdraw after the breeding season, joining flocks on the mainland for the winter.

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Food

Food Omnivore

Like many crow species, Northwestern Crows are omnivorous in diet and opportunistic in foraging. They eat invertebrates, small vertebrates, eggs, nestlings, carrion, fruit, seeds, and garbage. Like other crows, they forage mostly on the ground, singly or in groups, and sometimes hunt visually from a perch. Unlike many crow species, they readily wade into water to take marine invertebrates such as crabs, clams, whelks, sea urchins, and sand dollars, as well as vertebrates like small fish trapped in tidepools (especially blennies, gunnels, and pricklebacks). When hunting for prey, they submerge the head in tidepools, probe and dig into sand, mud, and soil, and flip over rocks, seaweed, and jetsam. For prey items with hard shells, these crows fly up above rocky shores or sidewalks and let the item drop, breaking open the shell. Northwestern Crows have been recorded eating the eggs of dozens of bird species, even of Peregrine Falcons, and they regularly prey on nestlings or fledglings. They also steal food from other birds, especially gulls and auks. Amphibians, small snakes, and songbirds are all known prey items, as are flying insects of many kinds, which are captured in the air. In summer, they eat blackberry, red elderberry, salmonberry, and Saskatoon berry. Like other crows, they visit landfills, garbage cans, picnic sites, and other places where human food or refuse might be available, and they are adept at getting at food left inside all sorts of containers. They scavenge at many types of roadkill as well as beached carcasses of whales and seals. When larger predators such as Bald Eagles make a kill, crows perch patiently nearby, waiting for an opportunity to scavenge scraps. If food is plentiful, Northwestern Crows cache (store) the excess, returning the next day to eat it. This behavior is especially important for a forager in the intertidal zone, as the mudflats are covered by deep water for much of the day. Their well-rounded diet may also include small bones, eggshells, and marine algae.

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Nesting

Nest Placement

Nest Tree

The male and female visit several sites together before selecting the nest site, often a concealed spot in a tree, shrub, or berry tangle, or on the ground against a tree or set in grasses.

Nest Description

Using branches up to a foot in length, the female constructs a sloppy-looking nest, then lines the interior with material such as grass, moss, bark, leaves, feathers, and wool. Nests are about a foot across and 9 inches tall, with the interior cup about 6 inches across and 4 inches deep.

Nesting Facts

Clutch Size:3-6 eggs
Number of Broods:1 brood
Egg Length:1.6-1.6 in (3.96-4.03 cm)
Egg Width:1.1-1.1 in (2.8-2.86 cm)
Incubation Period:17-20 days
Nestling Period:29-35 days
Egg Description:Blotchy pale green, blue, and gray.
Condition at Hatching:Blind and helpless; minimally covered in down.
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Behavior

Behavior Ground Forager

Northwestern Crows have long-term pair bonds, but they sometimes mate with crows that are not their partners. Males perform a flight display with slow wingbeats and rhythmic raising of the head. Prior to mating, the male droops and quivers the wings and tail and bows, and the female responds in kind, then crouches. Both male and female incubate the eggs and care for the young, sometimes with a “nest helper,” possibly offspring from a previous breeding season. Male and female often preen one another, and males bring food to females both before and during incubation. Beginning in February, pairs maintain territories, and all family members quickly mobilize to mob (harass) predators that come near the nest, calling, flying, and diving at them in coordinated attacks. On occasion, Northwestern Crow nests are located very near others, probably to provide better defense against predators such as hawks or owls. On other occasions, a crow pair may drive others of their species away from their territory, which a pair may occupy for many consecutive breeding seasons. After the breeding season, Northwestern Crows gather into large flocks, foraging, resting, and roosting together. These flocks have a complex hierarchy (a pecking order), with some individuals dominant over others and able to claim the best food or perches. Small flocks seen during the breeding season are probably nonbreeders. These highly social animals communicate visually as well as through a remarkable variety of calls. They often soar on clear days and sometimes seem to play with each other on the wing, chasing and swooping without aggressive purpose. Some also repeatedly drop, then catch, small objects while in flight, another form of play that has many practical applications.

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Conservation

Conservation Low Concern

Northwestern Crows are fairly common in their small range and their population was stable between 1968 and 2015, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 700,000 and rates the species a 10 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. Despite being protected by the Migratory Bird Treaty Act, Northwestern Crows are sometimes still shot for sport or other purposes, particularly in Canada. They are fairly tolerant of human activity, but in some residential areas people consider large evening roosts to be a nuisance and attempt to disrupt them.

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Credits

Lutmerding, J. A. and A. S. Love. (2019). Longevity records of North American birds. Version 1019 Patuxent Wildlife Research Center, Bird Banding Laboratory 2019.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

Verbeek, N. A. and Robert W. Butler. (1999). Northwestern Crow (Corvus caurinus), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

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