Northwestern Crow Corvus caurinus

Northwestern Crow Behaviour

Northwestern Crow Feeding, Hunting & Foraging Behaviour

Northwestern crows are well known to scientists for their ability to crack clams on rocks to open the shells. Crows find clams buried in beaches that they transport in their bills to rocks, wharves, paved walkways and roads where the clams are dropped until they break. In a series of ingenious experiments, Howie Richardson and Nico Verbeek (1986) showed that crows were adept at knowing the right size of clam that was worthwhile to crack open. They showed that crows often abandoned clams that were too small to carry to the rocks in favour of the large and more profitable clams. They decide on whether a clam is profitable or not by its weight (O’Brien et al. 2005).

Northwestern Crow Flight Patterns

Flocks of several thousand crows form in late summer in Victoria and Vancouver, British Columbia and Seattle, Washington to fly to evening roosts. The number of crows entering roosts numbers from a few birds to many thousands of individuals. The large communal roosts are used all year round but the greatest number is present from about October to March. In the early morning, crows return from the roost to feed in parks, suburban lots, farmlands, and beaches. Territory-holding crows in Vancouver defend territories through the winter and non-territorial crows forage as a group on the fringes. Near sunset, flocks begin to form to fly to the roosts. The flights to the roost can take some crows up 45-60 minutes to complete. The flights often involve tens or hundreds of crows that call to one another along the way. Their arrival at the roost is even more boisterous than their commuting flights. Calling, swooping, bowing and tail flicking displays are signs of their heightened anxiety. Why crows fly to roosts is not clear but it might have to do with predator avoidance. Red-tailed hawks and especially great horned owls are predators of crows. Unlike most songbirds that discretely enter roosts near where they feed, crows fly great distances to join in large numbers making a commotion. Possibly the raucous behaviour discourages predatory owls and hawks from waiting hidden to pounce on unsuspecting sleeping crows in the roost. Crows might use roosts to find a new mate, for warmth in winter, or to share information on the whereabouts of food.

Aggressive, Defensive & Territorial Displays of The Northwestern Crow

Crows vigorously defend nesting territories and bully other crows around food items. A threat display begins with the erection of feathers on the head held rigid over the shoulders. The bill is pointed slightly downward and the feathers on the belly and flanks are splayed. The accompanying photo shows a crow in a mildly aggressive posture. As aggression mounts, the wings droop ready to strike blows, and the tail is raised about 45^o off the horizontal. Fights are vicious affairs that begin with lunges of the feet, and jabs with the bill. The strategy is to pin the opponent to the ground and direct several hard jabs of the bill into the body. There is much slapping with the wings, snapping of the bill and squawking by the fighters.

Courtship & Breeding Behaviour of the Northwestern Crow

Crows are very secretive about their breeding behaviour. Pairs will be seen together preening each others feathers and around the eyes in a very tender fashion. During mating, the female crouches in front of the male who mounts on to her back. They push the tails aside and contact their cloacas. It is a quick affair after which the birds fly to a perch where they often preen.  

Northwestern Crow Nesting Habits

The northwestern crow begins to breed after its first birthday but nothing is known about when they establish breeding pairs. Nests are built beginning in late February and through March in trees and shrubs and on the ground on small islands. Both parents build the nest. Twigs provide shape to the nest and fine shredded cedar bark, moss, wool and grass stems form the lining. An average of 4 eggs is laid per nest in April, May and June and they hatch in May and June. Only the female incubates the eggs and her mate provisions her with food. This behaviour allows constant vigilance of the eggs and young chicks from other crows intent on cannibalizing them.  Chicks hatch naked with a few bits of down. They are fed by both parents and attain 80% of the adult mass of 310 g at about one month of age when they leave the nest. The adults continue to feed them as the young scramble about the branches near the nest for another week or two gradually following the parents on foraging forays. One brood of chicks is raised each year by both parents. Some pairs are assisted at raising the young by the previous year’s offspring. By July, families of crows make a racket when the young beg for food and the parents ward off cats, raccoons, dogs and humans that venture too close.

People are sometimes the recipient of the wrath of adult crows that swoop down from trees to peck or slap at heads. Crows are not villains – they are defending their nestlings. A careful search will likely reveal a recently fledged crow hiding in the shrubbery. Alfred Hitchcock’s horror movie The Birds has permanently etched into some minds that crows are villainous. Hollywood has done so much harm to the public view of wild animals.

Northwestern Crow Vocalizations 

Crows have a very wide repertoire of sounds whose meanings are largely unknown to us. They use some calls in a variety of situations that has left researchers confused to the meaning.  There is so much we do not know about crow society. People often ask if crows can speak. Although they utter a host of sounds, they do not appear to mimic noises around them unlike well known mimics such as the mynahs and starlings.