Loggerhead Shrikes: Breeding Endangered Birds for Release to the Wild
Ah, it is April, and that means it is time for me to be doing one of my favorite things—pulling out my extendable mirror and peeking into nests at our shrike breeding facility on the U.S. Navy’s San Clemente Island (SCI).
The San Clemente loggerhead shrike is a critically endangered songbird subspecies found only on SCI, and the Navy has been actively guiding and funding the recovery of this species for more than 20 years. It is a collaborative effort between the Navy, U.S. Fish and Wildlife Service, San Diego Zoo Institute for Conservation Research, the Institute for Wildlife Studies, and San Diego State University’s Soil Ecology Restoration Group. Other major collaborators from the past include the Western Foundation for Vertebrate Zoology, the Endangered Species Recovery Council, and PRBO Conservation Science.
When I first started on this project in the fall of 1998, the wild population had dropped to 14 adults, but through breeding birds in our facility and releasing them to the wild, we have had a dramatic effect on the wild population: by 2011, the breeding population numbered more than 170 shrikes!
At the beginning of this project, we stressed artificial incubation and hand-rearing, but now almost all chicks are parent reared. When parent shrikes rear their own chicks, they can teach them to be more wary of predators.
Though we don’t hand-rear, we do keep a close eye on them. From daily behavioral observations and twice-a-week nest checks, we can calculate expected hatch dates. Shrikes are mighty little hunters: they eat insects, lizards, mice, and other small birds. They feed these same foods to their chicks, but since they aren’t free to wander the island, we humans have to give them what they need. We use our Access database to help guide the amount of food needed based on the age and number of chicks.
This brings me back to my trusty extendable mirror, the kind mechanics use to peer under an engine, which is perfect for looking into nests. The long handle allows me to count the eggs while staying several feet away from the nest.
We pair our birds in the last week of March, and they quickly get busy courting and building nests. By the end of the first week in April, lots of eggs begin appearing, and hatching is expected before the end of April.
Ah, the end of April, which means I get to do another of my favorite things—photographing chicks in nests! Unlike eggs that are easy to count in my mirror, a pile of wiggly, pink, newly hatched shrike chicks are definitely NOT easy to count. Instead I whip out my digital camera, click twice, and clear out. Then I can peer at the pictures at my leisure, counting beaks and rumps. Sometimes it takes several recounts to convince myself that what first appeared to be four chicks is actually five.
About a week after hatch, our shrike parents become watchful and aggressive toward their human caregivers, dive-bombing and alarm calling when they spot us. This is the outward evidence of how parent shrikes instill wariness in their chicks, thus making them better survivors. And it is the release of these survival-ready juveniles that is our goal, helping grow the wild population.
Our continued success means the San Clemente loggerhead shrike may soon be a candidate for down-listing under the U.S. Endangered Species Act, making all the effort the Navy and their collaborators have put into this project well worth it!
Susan Farabaugh, Ph.D., Conservation Program Manager
Photos by Kathy De Falco, U.S. Navy; Daniel Clark, photographer; Susan Hammerly, U.S. Navy.