Buitron, D. 1983. Variability in the responses of black-billed magpies to natural predators. Behaviour 87. pp. 209-233.
Encounters between black-billed magpies (Pica pica) and a variety of natural predators were observed during 3 breeding seasons in Wind Cave National Park, South Dakota. Raptors were the most frequently encountered potential predators, with magpies reacting more strongly to falcons than to hawks. Reactions to crows and squirrels were most frequent and intense during laying and incubation, while raptors in flight and coyotes were responded to most vigorously during the second half of the nestling period and the first two weeks of fledging. Perched raptors were almost always mobbed vigorously. Diving to within 2 inches of a predator appeared to be effective in driving it away. The roles of chasing and alarm calling were less clear, but in addition to alerting mates and offspring to danger, such behavior would impede efficient hunting by the predator and so might contribute to its departure.