During a casual visit to the pinyon–juniper woodland of the southwestern USA, a visitor is likely to miss seeing one of the most interesting and characteristic birds of this habitat type, the Pinyon Jay (Gymnorhinus cyanocephalus). This omission is simply explained as Pinyon Jays are not dispersed uniformly over the landscape, but are clumped into large flocks that maintain very large home-ranges measured in square kilometers. Thus finding them is often like locating the proverbial ‘needle in a haystack’.

When a flock is located, however, an observer must be impressed by the noisy, raucous, gregarious, nature of these birds. Flocks of between 50 and 500 birds forage, roost, nest, and raise young together. Flocking is year round, and single birds are seldom seen. These tight units are particularly impressive when they become airborne and fly out of sight.

The Pinyon Jay, a robin-sized, blue bird ranges from Oregon and Montana to Baja California and Texas. As its name implies, this bird has a strong association with, and possible reliance on the pinyon pines (Pinusedulis, P. monophylla), which form an important component of the woodlands in the western USA. The relationship of the Pinyon Jay and the pinyon pines may be one of the best examples of plant–vertebrate co-evolution in North America. The bird receives nutrients, energy, nest and roost sites, and stimuli to breed from the pines, and in turn the tree relies on the bird for safe seed dispersal (Ligon 1978; Vander Wall and Balda 1981; Balda 1987).