The Pinyon Jay

Behavioral Ecology of a Colonial and Cooperative Corvid

By John M. Marzluff and Russell P. Balda. Academic Press Inc. (6277 Sea Harbor Drive, Orlando, FL 32887), 317 pages, 6-1/2 X 9-1/2, $37 cloth.

This is a book of many dimensions: the natural history of the Pinyon Jay; a theory of co-evolution between the pinyon pine tree and the Pinyon Jay; an embedded essay on natural selection; and a demonstration of how statistics and analysis can help ornithologists to develop a vivid portrait of a species' life.

By color banding each Pinyon Jay belonging to the "Town Flock," in Flagstaff, Arizona, and by analyzing masses of data over a 15 year period, the research team uncovered the structure of Pinyon Jay society.

The Town Flock lives peaceably year round on its mountainous home range, in a complex social system. Pinyon Jays mate for life and almost never divorce. The birds are not territorial and do not defend food supplies from other flocks. Daily activities are synchronized, as the birds forage together, cache seeds together, and roost together at night. During breeding season, the males arrive en masse on the colonial nesting ground several times a day to feed their incubating mates.

Pinyon Jays are closely associated with the pinyon pine, a conifer of the Southwest. Unlike other pines, whose survival strategy is to make nuts that are hard shelled and difficult to get at, this tree has evolved a seed that is large, soft shelled, and easily accessible to Pinyon Jays. Equipped with long, sharp bills and with expandable throats that can carry 50 seeds at a time, the birds harvest the ripening pine nuts in fall and bury the surplus, often several miles from their source. Although the jays are uncannily skillful at recovering their caches, some seeds sprout and become new trees. During the retreats of the glaciers during the Pleistocene Era, this partnership of bird and tree enabled the pinyon pine to leap farther than a seed will fall, and to colonize new areas rapidly.

Natural selection is a major theme of the book, as the researchers probe the selective advantage for each adaptation of Pinyon Jay biology. For example, the jays often attempt to nest too early in spring, when February or March snowstorms are likely to doom their efforts. The authors pondered how natural selection could allow such early nesting to persist. Their analysis revealed that the waste of energy is minimal, because if the birds fail they simply start over; and once in a while, when conditions happen to be right and late snows do not occur, those early nests produce a bumper crop of young Pinyon Jays. Hence the early nesting occasionally gives a big payoff in reproductive success, at little cost, and therefore is favored by natural selection.

The rigorous statistical bases for these and other conclusions are found in 44 tables and 116 figures, which will be useful to the scientific reader. Those who prefer to skip over the charts will still extract the meaning from the book, which is a good read, with a conversational style and frequent analogies between Pinyon Jay and human behavior.

Elegant ink drawings by Tony Angell and Caroline Bauder illustrate the book, along with black-and-white photographs by John Marzluff.

--Diane Porter