Loggerhead Shrike Program Making a Home Run

This is a long-term project to bring a severely endangered bird back from the brink of extinction. This shrike subspecies is only found on Navy-owned San Clemente Island (SCI). It was placed on the endangered species list in 1977, and the US Navy has been monitoring it, and doing all they can to recover the bird and its habitat while still conducting Navy training on the island.

In the early 1990’s the San Diego Zoo was approached by the Navy to start a captive breeding program. We maintain a captive population of 60-65 shrikes. We breed the flock to produce birds for release to increase the wild population, while maintaining a core flock for our captive population. We strive to increase the genetic diversity of both captive and wild populations through careful pair selection, and to produce the best possible birds that demonstrate the most normal behavior. This is best done by letting parents rear their own chicks, and by providing them with a captive environment that is as close to the wild environment as possible.

The captive facility is located on SCI, which makes them ready for the island climate. The birds are provided with live prey year-round so they will be skilled hunters after release.

Over the 18 years of this project, we have developed many new skills. In the beginning, methods to artificially incubate and hand-rear these small birds were developed by ZSSD Avian Propagation Center staff. Methods to monitor the behavior of the birds were developed by Behavioral Biology staff. Genetic diversity was close monitored, veterinary care was provided, and disease events explored by Wildlife Disease Lab staff.

In collaboration with the Navy biologists and the other contractors, we developed a complex array of soft release methods. We release captive adults to wild shrikes that can’t find mates, as breeding pairs released to empty shrike territories, as family groups from field aviaries, and we release juveniles in groups that mimic a clutch of wild juvenile shrikes dispersing from their home territory. With these methods we have successfully grown the wild population from as few as 14 birds to as many as 50 breeding pairs. Our goal is to reach the carrying capacity of the island. Once the goal is reached we should continue to monitor the population over time to track the dynamics and stability of the wild population.