Island Scrub-Jay Breeding Season 2011

Posted by Scott Sillett on September 14, 2011

The island scrub-jay (Aphelocoma insularis) is the only bird species in the continental United States to have never ranged to the mainland: it exists only on Santa Cruz Island off the coast of California.

We have studied its breeding biology and behavior since 2008 as part of a broader research program to understand the factors that limit and regulate the jay population. Our work is motivated by risks to the jay posed by its limited range and small population size, and by emerging threats from climate change and disease.

blue bird

We studied three plots on Santa Cruz Island from February to June in 2011. We found and monitored 130 jay nests. More than half the nests were predated and only 20 fledged young. Known nest predators include: island fox, Cooper’s hawk, Bewick’s wren, gopher snake, common raven, and other island scrub-jays. Most pairs made more than one nesting attempt. As in previous years, the average number of young fledged per territory was low relative to the average number of eggs laid. See chart below.

For only the second time in our study, we found a jay pair produce a second clutch after their first clutch fledged, a phenomenon called "double brooding." Their first nest fledged three young on April 25 and the female was sitting on a new nest in the second week of June.

We have another field season planned for 2012, and the focus will be on gathering more data on nesting and mating behavior as well as detailed studies of the survival and dispersal of juvenile birds.

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