Saving Shorebirds: Least Terns and Snowy Plovers

Some of the biggest benefits to living in San Diego are our weather and wonderful beaches. These two factors make this region important not only to us, but to other unique and interesting animals, such as the western snowy plover and the California least tern, which are federally listed as endangered and threatened, respectively. Both of these small bird species breed each year on undeveloped shorelines around San Diego County.

The San Diego Zoo Institute for Conservation Research has been involved in their protection and breeding enhancement since 2000.

Some of the biggest breeding colonies of the California least terns are located on Marine Corps Base Camp Pendleton and Naval Base Coronado; these sites also have some of the county’s highest nesting numbers of western snowy plovers.  Both Camp Pendleton and Naval Base Coronado are committed to maintaining a productive and pristine habitat that is properly managed as to not lose military training or conservation value over the long term, and this goal has resulted in site protection and monitoring of both species.

Thanks to our combined research and management activities, breeding sites at Camp Pendleton and Naval Base Coronado have become some of the most natural and highly productive sites in the State. 

Since 2010, the Institute’s Terns and Plovers Project team has been working side by side with Camp Pendleton and Naval Base Coronado biologists in developing an adaptive management and research program for both species. This program is geared around finding more efficient ways to monitor the species, as well as working out novel solutions to deal with current threats. 

One such threat is the impact of crows and ravens—they are excellent at finding camouflaged eggs and chicks on the beach and can wipe out entire nesting sites! Crows and ravens are natural predators, but their presence at tern and plover nesting locations is greatly elevated due to human recreational activities at adjacent camp sites and swimming beaches.

Our field technicians work closely on a daily basis with predator biologists to protect nests on the ground; but we are also exploring other long-term methods to decrease nest depredation, such as restricting corvid roosting and nesting locations near sites, decreasing their access to nearby garbage sources, and assisting with taste aversion studies.

Every day throughout the breeding season from March to August, our team crisscrosses the nesting beaches, keeping an eye out for fresh eggs and newly-hatched chicks. We mark the new nests to track their progress through the incubation period. Both the western snowy plover and California least tern chicks are “precocial,” meaning that soon after hatching, they leave the scrape in the sand that once constituted a nest and move off independently along the beach.
From this point onwards, the tiny snowy plover chicks forage and fend for themselves under the watchful eyes of their parents.

Although the tern chicks are very mobile, they await the return of their parents from their frequent fishing trips, which are somehow able to locate their own offspring amongst the maze of dune vegetation by recognizing each other’s unique calls. While the flightless tern chicks go through this dependency phase, we regularly catch them to obtain band numbers, and weight and wing measurement – all of which helps us track their survival and growth. Sadly, 2012 data suggests that many of the tern chicks have died of starvation – thought to be due to a scarcity of the tiny fish that the parents catch near the surface to feed their chicks.

Life on the shoreline is a challenge. Through the data we collect and the changes that we implement in and around breeding sites, we hope to provide both the western snowy plovers and California least tern with the best possible nesting habitat, which in turn enables the Marines and the Navy to make the most of this valuable, multi-use environment.

Joelle Fournier, Project Manager, San Diego Zoo Institute for Conservation Research.