The Yellow-billed Magpie (Pica nuttalli) is endemic to the Central Valley and coast ranges of California. A close relative of the Black-billed Magpie, it prefers oak savannah woodland and other areas with large trees scattered across wide open spaces.
The Yellow-billed Magpie closely resembles Black-billed Magpie, with black head and chest, white shoulders and belly, iridescent blue wings, and long tapered black tail. However, its bill is bright yellow. Bare skin behind eyes is also yellow, though not always clearly visible. Males are slightly larger than females. Otherwise, the two sexes are alike.
Distribution and Population Trends
The Yellow-billed Magpie is a nonmigratory endemic to California, west of Sierra Nevada. Range includes Sacramento and San Joaquin valley floors and foothills, and valleys of Coast Ranges from San Francisco Bay south to Santa Barbara County. In some areas, the species coexists with dense human settlement, but in other parts of the bird's former range, populations have declined or vanished in apparent response to development of housing or agriculture.
The bird inhabits open country with tall trees. It nests high in trees, predominantly in valley oaks and coast live oaks. Nests are very large (almost 1 meter across), made of sticks and mud. Egg-laying usually begins in late April; clutches generally have 6 or 7 eggs. The Yellow-billed Magpie forages mostly on the ground in grassland, agricultural fields, pastures, and barnyards, taking a variety of insects and occasionally, small mammals. Yellow-billed Magpies are highly social, foraging and roosting together often in large numbers. They are often seen aggressively mobbing predators or other perceived threats, including humans.
Habitat loss has already extirpated the species from parts of its historical range. Poison used for extermination of ground squirrels has been strongly implicated in the catastrophic decline of one California population, and declines from the 1800s are also linked to pest and predator control.
Of particular concern today is the impact from West Nile Virus in the 2004 and 2005, when large numbers of Yellow-billed Magpies are known to have perished. Studies conducted during that time indicated a rapid onset of the disease, leading to rapid fatality. This rapid onset, combined with the highly social nature of the bird, means that entire colonies could have been wiped out very quickly.