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Black-billed magpies are mid-sized birds with a long tail that represents up to half of their length. The head, upper breast, back, and tail are black and there are large patches of white on the wings and lower breast. They have heavy black bills and black legs. Sexes are similar in coloration, but females are about 10% smaller in size than males.
Black-billed magpies live in family flocks of six to ten birds. Larger groups of birds form communal roosts in the non-breeding season, consisting of up to several hundred birds. In cold weather, birds do not huddle together, but roost in coniferous trees with the branches acting as protection from predators and the wind. Like other members of the corvid family, mapgpies are highly intelligent birds. When kept captive from a young age, black-billed magpies can be taught to speak a number of words and phrases.
Known predators of black-billed magpies include American crows, common ravens, great horned owls, northern harriers, red-tailed hawks, weasels, mink, domestic cats, coyotes, and red squirrels. Groups of adult and juvenile birds cooperate in mobbing predators. This group behavior is usually effective in causing the predator to abandon the hunt. Black-billed magpies have different mobbing responses to predators that are most likely to attack at that particular stage.
Black-billed magpies, like other corvids, are opportunistic omnivores. They often forage for food on the ground and their diet can partially be determined by the small pellet that they regurgitate soon after eating. They primarily eat insects and their larva, as well as the eggs and hatchlings of songbirds. They also eat fruit and grain crops, and small mammals like mice and meadow voles. Black-billed magpies scavenge for carrion and are often seen along roadsides picking at road kill and human refuse. They often dig small depressions in the ground or the snow to store food.
Black-billed magpies form monogamous pairs throughout the breeding season and may form lifelong bonds. Both sexes help to construct an elaborate, domed nest, which may take between five and seven weeks to complete. The female is the primary defender of the nest prior to and during egg laying, and males become the defender of the nest during incubation. Like other members of the corvid family, the female is the sole incubator and is almost totally reliant on the male to feed her during this period. Because the sexes have specialized roles, if either mate dies during incubation, the brood does not survive.
Black-billed magpies breed from late March to early June, depending on location. There is usually one brood per season, although a second brood may be attempted if the first is not successful. Females lay up to nine eggs which are greenish-gray with brown markings. The first egg hatches within 25 days of being laid, hatching is asynchronous with usually only one chick hatching per day. The chicks are born without feathers and the eyes remain closed for seven days. Fledging takes place between 24 to 30 days after hatching. The parents feed the chicks in or near the nest for the first three to four weeks and the young are beginning to fend for themselves by six to eight weeks. Young become independent at about 70 days. Females are likely to nest in their first year, whereas males may not breed until their second or third year.
During the first half of the 1900’s, black-billed magpies were widely treated as pests due to their use of food crops, poultry, and livestock as part of their diet. Although determined efforts are still made to control magpie populations in certain agricultural areas, they are generally common throughout their range. Black-billed magpies are fully protected in the U.S. under the Migratory Bird Treaty Act but currently receive no protection in Canada.
University of Michigan Museum of Zoology Animal Diversity Web