Structure and Dynamics of Communal Groups in the Beechey Jay

Structure and dynamics of breeding groups in the cooperatively breeding Beechey Jay (Cyanocorax beecheii) were studied near Mazatlan, Mexico, from 1974-1978. Breeding groups were composed of one breeding adult member of each sex and 0-4 helpers, which varied in age from yearling to adult (3 years or older). Most groups were relatively stable in membership and occupied the same territories throughout our study. A few groups dissolved, most when habitat of their territory was destroyed. Adults predominated among birds moving from one group to another; neither sex predominated. Breeders that disappeared were replaced more often by immigrants than by group members. All group members assisted in feeding and defending nests, fledglings, and territories. Most helpers were offspring of one or both breeders. Male breeders accounted for the majority of the feeding visits, followed by female breeders and yearling helpers. Individual birds did not account for an increased percentage of feeding visits as they matured. A group attempted no more than one successful nesting and produced an average of 2.3 fledglings per year. Major losses of eggs were through predation (15 of 99) and infertility (21 of 84). Predation was the principal source of nestling loss (25-33 of 40 lost, of 101 total). Groups with helpers did not realize an increase in annual reproductive success when compared to groups without helpers. The probability of survival increased with age; adult annual survival rate was at least 70% and probably nearer to 80%. Only one known bird failed to breed after reaching adulthood and at least 29 of 34 adults became breeders. Breeders incur few costs in allowing helpers to remain on the territory and assist at the nest. They probably benefit from the presence of helpers through increased survival and thus in lifetime reproductive output. Helpers forego breeding and remain on occupied territories because by doing so they have a greater opportunity to survive and ultimately reproduce than if they dispersed into ecologically unsuitable, unoccupied areas. Likely reasons that helpers help are that such behavior (1) is a form of payment to the breeders for allowing them access to territorial resources, (2) results in the gain of future help of the young they help raise, and (3) increases their indirect fitness because they help close kin. Any combination of these reasons may be operative. The social organization and demography of Beechey Jays are remarkably similar to thos