Distinguishing Island and Western Scrub-Jays

Feb. 10, 2005

In late October 2004 I was privileged to visit the Nature Conservancy’s spectacular Santa Cruz Island preserve off the coast of Southern California. This island, along with the other California Channel Islands has been called the “Galapagos of the North” and has long been the focus of biological studies, but became more interesting for North American bird watchers around 1995 when the American Ornithologist’s Union elevated the Island Scrub-Jay to a full species separate from the mainland Western Scrub-Jay. The entire world’s population of about 12,500 Island Scrub-Jays is found on Santa Cruz Island and the species has never been recorded anywhere else. This was my first visit to the Island and consequently my first opportunity to see the Island Scrub-Jay in life.

I illustrated this species in my Sibley Guide to Birds (2000) but having never seen it I was forced to work from specimens, photographs, and expectations based on my familiarity with Western Scrub-Jay. Seeing the birds in life revealed a number of small differences and clarified the most useful distinctions, and it is worth summarizing that information here to update the guide.

At first glance anyone even moderately familiar with Western Scrub-Jay will be struck by the large bulk and dark color of the Island Scrub-Jay. They average 15% larger in measurements and 40% larger in weight, with the bill 20% longer than in Western Scrub-Jay (Curry and Delaney, 2002).

These differences, which are probably striking to someone who sees mainland jays regularly, are subjective and relative differences and may not lead to a fully satisfying identification. In looking more closely at plumage details I noticed several specific things that seem quite distinctive and should be useful as confirmation.

• The Island Scrub-Jay has deep bluish-black cheeks, contrasting distinctly with the paler blue of the crown and nape. The nasal tufts at the base of the bill are nearly black and the feathering around the eye is nearly black. On Western Scrub-Jay the cheeks and nasal tufts are dark bluish-gray, not much darker than the surrounding blue parts.
• The white eyebrow of Island Scrub-Jay is narrow and broken, apparently consisting of a single row of feathers, and not extending forward of the eye. On Western Scrub-Jay the white eyebrow is broader and longer, and extends as a band of tiny white flecks forward to the base of the nasal tufts and around below the eye.
• The mantle of Island Scrub-Jay is a dark blue-brown, so dark that it contrasts very little with the surrounding blue of the wings and nape. On Western Scrub-Jay the mantle is a paler gray with less obvious blue and brown tones and contrasting distinctly with the surrounding blue, especially the darker blue of the “necklace”.
• The under tail coverts of Island Scrub-Jay are washed with blue. The under tail coverts of Western Scrub-Jay from the adjacent mainland are white (although it is important to note that Western Scrub-Jays from farther north along the Pacific Coast have blue under tail coverts).
• The darker blue color of Island Scrub-Jay is always apparent, especially on the wings and tail and on the blue partial necklace. The blue color of Western Scrub-Jays on the Pacific coast is a relatively pale, dusty blue (and birds of the interior western subspecies group ‘Woodhouse’s’ Jay are even paler and drabber).
• The Island Scrub-Jay is relatively quite and inconspicuous, much less vocal than their mainland relatives, and their calls are muffled, flat, and low-pitched; lacking the vibrant, electric, rasping sound of mainland birds. The rising “zhink” call so characteristic of mainland birds is given infrequently by Island Scrub-Jay and only as a flat or slightly descending “sshrr”. The characteristic rapid series of harsh notes is also relatively flat, muffled, and soft, as if vocalizing through a beak full of food.
• Flight and habits are similar but the larger size and bulk of Island Scrub-Jay is apparent. In addition to the longer and stronger-looking bill the whole head appears longer and the neck thicker than Western Scrub-Jay.
• The bill shape seems slightly different, with Island Scrub-Jay having a nearly straight culmen and thick lower mandible; the bill looks strong, thick, and straight. It also has an obvious silvery sheen on the base of the bill around the gape, more obvious than on Western Scrub-Jay, maybe because it contrasts more with the blacker feathers.

Island Scrub-Jay has never been recorded away from Santa Cruz Island and mainland Scrub-Jays have never been recorded on any of the Channel Islands. This is not likely to change, but it is certainly worth watching for either species outside of its normal range. Just knowing the differences allows a fuller appreciation of the uniqueness of the Island Scrub-Jay.

References:

Curry, R. L., and K. S. Delaney. 2002. Island Scrub-Jay (Aphelocoma insularis). In The Birds of North America, No. 713 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA. http://bna.birds.cornell.edu/BNA/