Island Scrub Jay - Taxonomy

Taxonomy

The Island Scrub Jay was first described by American ornithologist Henry Wetherbee Henshaw in 1886. This bird is a member of the crow family, and is one of a group of closely related North American species named as scrub jays. These were formerly often considered as a single species, the Scrub Jay, Aphelocoma coerulesens, with five subspecies, but full species status is now normally given to the Florida Scrub Jay, A. coerulesens, the Island Scrub Jay, and the Western Scrub Jay, A. californica, the latter having three subspecies across its extensive range. The relationships within the genus are not fully resolved: the Western Shrub Jay subspecies A. c. californica may be another candidate for species status, and some authorities already split it into Californian Scrub Jay, A. californica, and Woodhouse's Scrub Jay, A. woodhouseii. The DNA studies also indicate that the island and coastal forms have long been isolated from their relatives inland.

The scrub jays seem to be incapable of crossing significant bodies of water. The Island Scrub Jay has never been recorded on neighboring Santa Rosa Island, only about 10 km (6 mi) away, and there are no definite occurrences of a scrub jay on any other of the Channel Islands, or on the Coronado Islands, only 13 km (8 mi) from the mainland. It has been suggested that the ancestor of the present population was storm-borne or carried on driftwood to Santa Cruz, or that the colonization occurred during a period of glaciation 70,000 to 10,000 years ago, when sea levels were much lower and the channel between the coast and the islands was correspondingly narrower. More recent DNA studies show that, although other island endemics such as the Island Fox and the Santa Cruz Mouse may have diverged from their mainland relatives around 10,000 years ago, the scrub jays separated in a period of glaciation around 150,000 years ago. Up to about 11,000 years ago, the four northern Channel Islands were one large island, so the ancestral Island Scrub Jay must have been present on all four islands initially, but became extinct on Santa Rosa, San Miguel and Anacapa after they were separated by rising sea levels.