Since 1989, the San Diego Zoo Institute for Conservation Research, in conjunction with the United States Navy, has been making great efforts to recover endangered San Clemente loggerhead shrikes by breeding them in aviaries and releasing juveniles into the wild. Because of the efforts of the Zoo, the Navy, and those of partner conservation organizations, this shrike subspecies, which occurs only on Navy-owned San Clemente Island off the coast of California, has increased from a population of 14 individual birds in 1998 to 65 breeding pairs in 2013. Although there is much work yet to be done, the recovery program’s success story is well known. But what exactly goes into such a project? More interestingly, what goes into the busiest, most critical part of the year for the program? How does the busiest, most critical part of the year—the breeding season—even begin for the shrikes and staff of the San Clemente Loggerhead Shrike Breeding Program?
The breeding effort begins in January, when we receive a very exciting document delivered by Tandora Grant, the San Clemente loggerhead shrike’s studbook keeper. It is her responsibility to use genetic and demographic statistics to determine which of our shrikes to breed each year. Two important factors that come into play during Tandora’s matchmaking are the representation of our birds’ genes in the wild population’s gene pool and each of our bird’s personal breeding history. It is vital to balance these two factors to maximize the positive impact our program has on the recovery of the shrike; too few juveniles to release at the end of the season results in a low probability of their surviving to breed the next year, but releasing many genetically invaluable juveniles is potentially detrimental to the recovery of the species. Think Fiddler on the Roof meets conservation biology; the document Tandora delivers is the year’s breeding recommendations, and it contains the season’s breeding pairs, whether the birds are happy with her choices or not! More often than not, the birds are happy, but the document also contains alternate pairings should any of the chosen shrikes display a lack of motivation when it comes time to court each other.
In the first week of February, after we have prepared the breeding aviaries for the upcoming season, the select females are moved into aviaries adjacent to their males in a logistics puzzle that has been appropriately named “The Big Move.” You can imagine how hard it is to place 12 to 15 specific pairs next to each other in appropriately outfitted breeding enclosures when we have a flock size of over 60 birds and a grand total of about 80 enclosures! Though it is sometimes difficult and requires lots of planning, a little bit of luck, and plenty of cooperation from the shrikes, The Big Move is important, because it is designed to imitate the natural movement of wild shrikes.
In the wild, male and female San Clemente loggerhead shrikes maintain exclusive and solitary winter territories; however, come breeding season, females leave their winter grounds to search for attractive mates. By moving a specific year’s breeding males into their breeding enclosures and the female’s into enclosures adjacent to their chosen mates, we aim to simulate the female’s discovery of her mate. Once the breeding pairs have been placed in their adjacent enclosures, they have entered the “pre-pair” phase of the breeding season. This is the time for the males to court the females by displaying, singing, nest building, and most importantly, feeding them lots of bugs! If all goes well, we will be able to move on to the next phase—pairing.
Henry Fandel is a research associate for the San Diego Zoo Institute for Conservation Research.