The Island Scrub Jay -- Cause for Concern

Painting by Eli W. Blake Jr.
December 1886
(From Collins 2009)

The Island scrub jay (Aphelocoma insularis) is found only on Santa Cruz Island, the largest of the eight California Channel Islands. It is the only bird island endemic in the continental United States. (An endemic is a species unique to one location and found nowhere else.) Estimates of the population size for Island scrub jays has varied over time and between studies. Generally speaking, older studies estimated a larger population size than more recent studies, suggesting that the population has declined.

Wildlife biologists studying the birds cannot confirm a population decline, but the present-day estimate (2500) is small enough to concern them for several reasons. First, of course, this population is restricted to a single island, increasing the likelihood that one catastrophic event (like a fire) could jeopardize the entire species. Quite literally, their eggs are all in one basket! Second, a population size of 2500 is smaller than that of other bird species designated as endangered by the US federal government (e.g. the Red-cockaded woodpecker). A third reason for concern is that when island populations of other species have declined, they have often declined very rapidly, leaving little time for addressing, or even detecting, the decline. 

Taking Proactive Measures

The Nature Conservancy (TNC) and the National Park Service (NPS) each own part of Santa Cruz Island. They have opted for a proactive stance on Island scrub jay conservation, taking steps now to reduce the chances that the species ever flirts with extinction. They have outlined four courses of action:

1. Establish a small captive population to study breeding behavior, so that if captive breeding of the Island scrub jay is necessary, they won't have to learn under the gun.
2. Vaccinate a subset of the population against the West Nile Virus, which is deadly to other members of the crow family. A similar vaccination program has successfully protected the endangered California Condor from this disease. As of 2012, about 100 Island scrub jays have been vaccinated. 
3. Develop protocols to prevent, detect, and respond to biohazards like introduced rats, invasive plants, and wildfires.
4. Establish a second population on Santa Rosa Island.

Island scrub jay nest
(Photo from MBC site)

This last option, of course, is the most controversial action that the group is contemplating. Their rationale is that a Santa Rosa population would spread the "eggs" to another basket, reducing the chance that a single event could wipe out the species. In addition, there are tantalizing suggestions that Island scrub jays lived on Santa Rosa Island until the late 19th century.

Island Scrub Jays on Santa Rosa Island?

Two bits of evidence point to a now-extinct population of Island scrub jays on Santa Rosa Island.

Scientists have found one fossilized femur of an Island scrub jay on the island. Radiocarbon dating places it at 10,000 to 28,000 years old. One femur seems like paltry evidence for scrub jays on Santa Rosa, but fossil evidence of birds this size are hard to find on any of the islands. For example, there are no fossilized remains of Island scrub jays from Santa Cruz Island and we know the bird is there today.

The other whiff of scrub jay from Santa Rosa is from the field notes of the ornithologist Clark Streator, who visited the island in 1892. He interviewed John More, a sheep rancher on the island, and recorded this comment in his field notebook: "Aphelocoma -- Mr. John More informs me that there are Jays on the island."

That's it -- a bone and a sentence in a field notebook.

Could scrub jays have gone extinct on Santa Rosa Island without any iron-clad record of it ever occurring there? It seems possible. The species was first mentioned by H. W. Henshaw in 1876 and not formally described as a new species until 1886. During this time sheep grazing was rapidly degrading the island's habitat so that it was unsuitable for scrub jays. In addition, only a handful of naturalists visited the islands before the turn of the 20th century and many of them did not record any bird sightings. Thus, it might have gone extinct on the island before its presence was firmly established.

How would the Island scrub jay have gotten to Santa Rosa? It isn't a strong flyer -- vagrant Island scrub jays are never found on other Channel Islands.

But scrub jays wouldn't have had to fly to get to the other Northern Channel Islands! Sea level dropped during glaciation events, combining the four northern islands into one single large island (Santarosae). This happened perhaps 8-10 times over a 200,000 year period. Genetic studies suggest that Island scrub jays would have been on the islands during many of these cycles. During periods of low sea level, the birds could have spread throughout Santarosae, only to be isolated on separate islands during times of higher sea level.

The Northern Channel Islands (brown) and Santarosae (green)
(From Collins 2009)

The last Pleistocene glaciers retreated around 10,000 years ago, stranding scrub jays on the four modern islands. At some later time the populations on San Miguel, Anacapa, and Santa Rosa went extinct, leaving only the Santa Cruz population of birds. San Miguel and Anacapa probably never had much habitat that was suitable for scrub jays and it most likley went extinct on those islands quickly. But Island scrub jays might have survived on Santa Rosa until the 19th century. And, in the near future, they might be coming back.

References:

Collins, P. W. 2009. History and prehistoric record for the occurrrence of Island scrub-jays (Aphelocoma insularis) on the Northern Channel Islands, Santa Barbara County, California. Santa Barbara Museum of Natural History Technical Reports - No. 5.

Morrison, S. A., et al. 2011. Proactive conservation management of an island-endemic bird species in the face of global change. BioScience 61: 1013-1021.

For more information:
The Migratory Bird Center (MBC) at the National Zoo is involved in Island scrub jay conservation efforts.  Conservation measures are described in this article.

 The Nature Conservancy information on West Nile virus and Island scrub jays

The Santa Barbara Museum of Natural History offers a wealth of information about the Channel Islands, especially the northern islands.