Island Scrub-Jay Aphelocoma insularis Scientific name definitions

In 1875, naturalist Henry Henshaw completed a short visit to Santa Cruz Island, largest of southern California's northern Channel Islands off Santa Barbara and only 30 kilometers from the nearest point on the mainland. During his visit, Henshaw collected 4 large and brightly colored scrub-jays, which, after comparison with mainland specimens, he concluded represented a new species, Aphelocoma insularis (1 Henshaw, H. W. (1886). Description of a new jay from California. Auk 3:452-453. Close ). This island endemic population averages about 15% larger, 40% heavier, and with a bill about 20% longer than the largest mainland scrub-jay, the California Scrub-Jay (Aphelocoma californica).

Henshaw's large scrub-jays are known only from Santa Cruz Island, and no scrub-jays are currently found on any of the other Channel Islands, even as a vagrant. In addition, the Island Scrub-Jay is the most strongly differentiated of the endemic landbirds found in the archipelago (2 Swarth, H. S. (1918). The Pacific Coast jays of the genus Aphelocoma. University of California Publications in Zoology 17:405-422. Close ). Although isolated and distinctive, its close similarity with other scrub-jays has caused taxonomists to treat it in the past as a subspecies along with all other scrub-jays in western North America and with the highly disjunct populations in Florida (3 Pitelka, F. A. (1951) Speciation and ecological distribution in American jays of the genus Aphelocoma. University of California Publications in Zoology 50: 195–464. Close ). Accumulated information on behavior, morphology, and genetics has since supported recognition of 5 species of scrub-jays (4 Chesser, R. T., K. J. Burns, C. Cicero, J. L. Dunn, A. W. Kratter, I. J. Lovette, P. C. Rasmussen, J. V. Remsen, J. D. Rising, D. F. Stotz, and K. Winker (2016). Fifty-seventh Supplement to the American Ornithologists’ Union Check-list of North American Birds. Auk 133(3):544–560. Close ). Its status as a distinct species is based on traditional morphological criteria bolstered by genetic analysis (5 Peterson, A. T. (1990). Evolutionary relationships of the Aphelocoma jays. University of Chicago Press, Chicago, IL, USA Close , 6 Peterson, A. T. (1992). Phylogeny and rates of molecular evolution in the Aphelocoma jays (Corvidae). Auk 109:133-147. Close , 7 Delaney, K. S., S. Zafar, and R. K. Wayne (2008). Genetic divergence and differentiation within the Western Scrub-jay (Aphelocoma californica). Auk 125(4): 839-849. Close ).

Besides its endemism and large size, the Island Scrub-Jay is notable in several other respects. As is often typical of island birds, the jays of Santa Cruz Island are locally common, fearless of humans, and inquisitively opportunistic in their foraging habits. Intensive study of their evolution, demography, and social ecology has revealed that the endemic birds are intermediate between California Scrub-Jay and Florida Scrub-Jay (Aphelocoma coerulescens) in several important respects: while Florida Scrub-Jay is renowned for its extreme habitat specificity, highly restricted dispersal, and cooperative breeding (8 Woolfenden, G. E., and J. W. Fitzpatrick. (1984). The Florida Scrub Jay: Demography of a Cooperative-breeding Bird. Princeton University Press, Princeton, NJ, USA. Close , 9 Woolfenden, G. E., and J. W. Fitzpatrick (1996). Florida Scrub-Jay (Aphelocoma coerulescens). In The Birds of North America, No. 228 (A. Poole and F. Gill, Editors). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C. Close ), California Scrub-Jay is more flexible in its habitat requirements and less social throughout most of its broad geographic range (10 Curry, R. L., A. T. Peterson, and T. A. Langen (2002). Western Scrub-Jay (Aphelocoma californica). In The Birds of North America, No. 712 (A. Poole and F. Gill, Editors). The Birds of North America, Inc., Philadelphia, PA. Close ); Island Scrub-Jay displays limited dispersal imposed by the constraints of habitat and physical space in their island range and concomitant delayed breeding, but without any evidence of cooperative breeding indicated by observations of helpers at the nest. An important driver of the social system of the Island Scrub-Jay is an adult survival rate of more than 90% per year among both breeders and nonbreeders, levels that are extra-ordinarily high for a passerine bird.

Despite the intriguing combination of island endemism, gigantism, and unusual demography, many aspects of the Island Scrub-Jay's biology remain unknown, in part because of the logistical challenges of conducting field research on an offshore island. This account focuses on topics for which at least some information exists, including comparisons with mainland relatives where possible. Ample opportunities exist for further research on the unique Island Scrub-Jay, which is joined by only the Yellow-billed Magpie (Pica nuttalli) as a bird species endemic to California.