The San Clemente loggerhead shrike (Lanius ludovicianus mearnsi; SCLS) is endemic to San Clemente Island (SCI), California. Due to its localized range, critically low population numbers, consistently low productivity, predation pressure from non-native species and habitat degradation by feral goats (Capra hircus), this subspecies was listed as federally endangered in 1977. Throughout the 1990s, the population size of wild SCLS remained extremely low, with estimates ranging from 33 individuals in 1994 to only 14 individuals in January 1998.
Due to the critically low numbers of shrikes in the wild population, intensive efforts were necessary to decrease the threat of extinction in the wild. IWS first became involved with the SCLS program in 1996 with the development of video monitoring systems that could be used to determine the reasons behind shrike nest failures. In 1997 the U.S. Navy contracted with IWS to develop a research protocol that could be implemented to provide a better understanding of shrike habitat requirements and to propose improved methods for successfully releasing captive-bred shrikes into the wild. In 1998 the Navy requested that IWS start implementing some of the research suggestions that were made in the report.
In 1999 our involvement with the recovery effort grew to include taking over the release of captive-reared shrikes into the wild. In collaboration with the San Diego Zoo, IWS implemented new release protocols which resulted in the first captive reared shrikes being successfully recruited into the wild population. We have since made numerous modifications to our techniques and released a total of 434 shrikes on San Clemente Island.
Also beginning in 1999, we were contracted by the U.S. Navy to administer a predator research and management program, which focused on innovative methods to monitor native predators and protect SCLS nests from predation. Shrikes are impacted by a variety of introduced predators, including black rats, and controlling their numbers within shrike nesting territories increases the probability of successfully fledging young.
Checking for wing wear/molt Checking for parasites Weighing shrike in a bag
In 2006 IWS took over the responsibilities of monitoring the wild shrike population on San Clemente Island. This work involved attempting to locate all nesting shrike pairs, determine their success, band as many nestlings as possible, trap shrikes outside the nesting season for color marking, and resight birds over the winter to estimate survival.
Under the recovery effort funded by the U.S. Navy, the shrike population has rebounded and is showing very positive growth in population size.
The minimum number of breeding individuals in the wild population of San Clemente loggerhead shrikes on San Clemente Island, California, separated by origin (wild-born vs. captive-reared), 1991–2009. Arrow indicates the year that IWS started releasing captive-reared birds into the wild population.
The Institute for Wildlife Studies (IWS) is proud to be a member of the recovery effort of this imperiled songbird, working cooperatively with the U.S. Navy, U.S. Fish and Wildlife Service, the Zoological Society of San Diego, and the Soil and Ecology Restoration Group of San Diego State University.