San Clemente Loggerhead Shrike Captive Breeding Program

Since 1991, the Zoological Society of San Diego (ZSSD) has been involved in the recovery of the San Clemente Loggerhead Shrike (Lanius ludovicianus mearnsi), one of the most endangered passerines in North America. This shrike is found only on U.S. Navy-owned San Clemente Island, the southernmost island of California’s Channel Islands, and an essential training base for the U.S. military. The bird was federally listed as endangered in 1977, and surveys in the mid-1980s found that as few as five breeding pairs remained. In 1990, the Navy approached the ZSSD to develop a captive breeding program to provide a reservoir of genetic material, a hedge against catastrophic events, and a source of animals for release to augment the wild population.

At present the program involves a full-time staff of seven members of the Applied Animal Ecology Division of CRES, who live and work on the island, directly caring for and monitoring the captive flock. The island staff is supported by many other ZSSD departments and CRES Divisions including Veterinary Medicine, Wildlife Disease Laboratories, Avian Propagation Center, Nutrition, Behavioral Biology, and Genetics.

The initial captive effort involved groundbreaking advances in the development of protocols for artificial incubation and hand rearing of this small altricial passerine species using the mainland shrike as a surrogate (Kuehler et al., 1991). A captive flock was founded in 1991 with the collection of ten eggs and nestlings from SCI, six of which survived to produce offspring the following year. Periodically, eggs, nestlings, and adults have been transferred from the wild to diversify the captive flock, and since 1999, adult and juvenile releases have supplemented the wild population. Genetics and demography are managed intensely for the captive flock, and opportunistically for the wild, by CRES population biologists trained by the AZA’s Small Population Management Advisory Group. Priorities for management are optimizing genetic diversity in the captive flock, as well as providing a number of genetically diverse individuals for release sufficient to overcome the demographic challenges facing the wild population.

To achieve better results in captive breeding, a detailed behavioral monitoring program was developed in 1994 to assess mate compatibility before pairing, to monitor the pairs during breeding, and to assess the foraging and flight skills of the captive candidates for release. The information gleaned from the behavioral observations in captivity and the wild has been incorporated into our avian husbandry protocols to best produce captive hatched birds that can survive and breed in the wild. These protocols were also an important part of the successful release program that was developed by all the program collaborators in 1999.

The success of our program can be seen in the remarkable growth of the wild population, a direct result of the successful release protocols initiated in 1999. From a population consisting of few as four breeding pairs in 1998, and fewer than ten hatched chicks by 2006, the wild population has grown to over 40 breeding pairs that hatched over 160 chicks. From 1991 to 2006, over 300 captive-bred shrikes have been released to the wild, and over 50 have survived and bred successfully in the wild. Today, over 80 percent of the wild population is comprised of captive-hatched birds and their descendents.