Introduction

The Mexican Jay, also known as the Gray-breasted Jay, is a highly social species of the mountains of central and northern Mexico. It ranges north into the “sky islands” of Arizona, New Mexico, and western Texas. Resident in pine-oak-juniper woodland, it relies on acorns and pinyon nuts to survive the winter.

This species’ social organization, based on defense of permanent territories by groups of 5 to 25 individuals, is one of the most complex known for birds. Within each territory, 2 to 4 females may breed simultaneously and somewhat monogamously. The young are fed not only by their own parents but also by many other group members, namely other breeders, failed breeders, and some nonbreeders.

The Mexican Jay is strictly nonmigratory and has little or no dispersal from its natal group, probably being more extreme in this respect than any other North American bird. It may live up to 20 years, often in the company of its offspring, parents, siblings, and other relatives on the territory where it was hatched or on an adjacent one.

A color-banded population of the Mexican Jay was studied every year for 26 years (1969–1994) at the Southwestern Research Station (SWRS), in the Chiricahua Mountains of southeastern Arizona by the author, Esther R. Brown, and others. Unless otherwise noted, all observations reported here on natural populations refer to this study and will not be further acknowledged.