The Pinyon Jay is a highly social, cooperative-breeding, seed-caching bird of the foothills and lower mountain slopes of the western and southwestern United States. Although omnivorous, it is committed to the harvest, transport, caching, and later retrieval of pine seeds, aided by a relatively long, strong bill; an expandable esophagus; and long, strong wings. Individuals have excellent spatial memories that allow them uncanny recovery accuracy when digging up their hidden food stores months after caching, even through snow.
This bird is named for piñon pines of western North America (genus Pinus, subgenus Strobus, subsection Cembroides; Little and Critchfield 1969 ). These pines and this jay are associated in a mutualist, or coevolutionary, relationship. The large, wingless seeds of these pines are dispersed long distances on the strong wings of the Pinyon Jay, which reaps the reward of a food source rich in energy and nutrients.
Social organization is complex in this bird, with permanent flocks that may contain more than 500 individuals. Many birds spend their entire lives in their natal flocks. Individuals that do disperse—mostly females before they are one year of age—generally travel short distances. Birds may live up to 16 years of age in the wild and in captivity. Although permanent residents, in years when cone crops fail, individuals often disperse far from their normal range, making them one of the truly “irruptive” species of North American birds.
The Pinyon Jay is a synchronized colonial nester that commences breeding in the cold of winter in areas where pine-seed crops were abundant the previous autumn. This is one of the earliest nesting passerines in the United States. Nests are bulky and well insulated and often are placed on the south side of tree foliage—usually one to a tree and scattered throughout a traditional breeding ground that is used almost every year. At some nests, yearling males help provision their brothers and sisters. Young from multiple nests gather in crèches, which may number in the hundreds of individuals, where they are fed predominantly by their parents; this requires exacting individual recognition. In these crèches, young birds preen each other and exert dominance over their associates and are subject to severe predation.
Autumnal breeding by this species occurs in a single population in central New Mexico, when piñon pine–cone crops are large. Physiologically, the mere presence of pine seeds and green cones reverses gonadal regression and stimulates testis growth in wild and experimental birds, triggering breeding (Ligon Ligon 1974b , Ligon 1978 ).
Agencies of federal and state governments have had a systematic, well-funded program for over 60 years to eradicate large areas of this species' normal habitat, piñon-juniper (Juniperus spp.) woodland, and turn it into pasture land for grazing cattle.
A color-banded flock, called the Town Flock, was studied in and around Flagstaff, Arizona, for more than 18 years by the author and many of his students; members of his family; and a local amateur, Gene Foster. This work culminated in a publication, The Pinyon Jay: Behavioral Ecology of a Colonial and Cooperative Corvid, by J. Marzluff and the author ( Marzluff and Balda 1992 ). In addition, excellent work by J. D. Ligon and his students in New Mexico provides much of the information used to write this account. Thus, most of what is known about this bird comes from or near the southern edge of its range.