The Black-billed Magpie is medium-sized and boldly patterned. Sexes similar in appearance, and plumages similar throughout year. Adults largely black, with contrasting white scapulars, white belly, iridescent metallic blue-green wings and tail, and large white markings on primaries (rarely on secondaries), with form white patch on wing when wing is extended. Tail long and graduated. Sexes distinguished by differences in size. Males are larger (Trost 1999).
For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see Marks et al. 2016, Birds of Montana.
Western Hemisphere Range
Historically, it frequently followed Native Americans and lived on the refuse of their hunts. In breeding season will be found in thickets in riparian areas, often associated with open meadows, grasslands, or sagebrush for foraging. Less specific in its habitat requirements in nonbreeding season. Frequently numerous near human habitats such as livestock feedlots, barnyards, landfills, sewage lagoons, and grain elevators (Trost 1999).
Ground-dwelling arthropods, seeds, and carrion (Trost 1999).
South of Missoula nesting density was 55.5 pairs per square mile; nesting range averaged 0.39 miles in diameter; and feeding territory averaged 400 feet in diameter. Humans and pine squirrels caused 14% and 12% of nesting failures. The Great Horned Owl is also a predator.
Nests are durable, domed structures of sticks, with mud cup and anchor. Generally prefers high trees. Have been know to nest on utility poles. Eggs usually subelliptical in shape, and tan or olive brown colored background with speckles (Trost 1999). South of Missoula the average clutch size was 6.5; 58% hatched; 88% of the young fledged; and the minimum breeding age was 1 year. Statewide, egg dates range from March 28 to May 26.