Social Interactions in the Santa Cruz Island Scrub Jay

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Abstract
Social interactions were studied in the genetically isolated Santa Cruz Island scrub jay (A. coerulescens insularis) over 5 yr. A total of 254 individuals, representing most of the population within an approximately 225-ha study area, were color-banded. This jay resembles known western mainland populations in its breeding biology and the general characteristics of its social system. Pairing is permanently monogamous; breeders defend established territories throughout the year. This subspecies may include a higher percentage of non-breeding individuals, especially those older than 1 yr of age, than poorly studied western mainland populations. Populations of both the Santa Cruz Island scrub jay and Florida scrub jay (A. c. coerulescens) appear to saturate suitable nesting habitat. Mortality rates are low; both populations produce individuals who delay breeding for up to several years. Unlike the ecologically restricted florida scrub jay, the Santa Cruz Island scrub jay is ecologically broad, enabling non-breeders to maintain themselves in marginal habitats until such time as breeding space becomes available; cooperative breeding does not occur in A. c. insularis. When dispersal from natal territories is ecologically feasible, selection does not favor the evolution of group-breeding behavior. The selective value of non-territorial, floating behavior by non-breeding Santa Cruz Island scrub jays presumably outweighs any possible benefits that might be derived through kin selection. At least in this species, the theory of habitat-forced cooperative breeding appears to explain most of the currently known range of social interactions.

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