An adult CA least tern incubates its eggs. Credit: D. Robinette
California least terns are small seabirds that make their nests in the sand, at beaches and tidal flats. Their eggs are sand-colored and their chicks are perfectly adorable, and totally vulnerable on the ground at the beach. It’s no wonder the birds are endangered: the species basically tries to raise its chicks on our favorite playground.
Least tern chick. Credit: D. Robinette.
If you’ve seen roped off areas at beaches – Tijuana River Estuary, for example – it’s often to protect these vulnerable ground nesters, and it’s working, amazingly, even with more than 25 million of us in coastal counties of California. According to the U.S. Fish and Wildlife Service, California least tern numbers have jumped more than 10-fold since the bird’s were listed in 1973. Nature has such amazing resilience sometimes.
Least tern parent and chick. Credit: D. Robinette
Not every year, though, brings success to their recovery, and last year most of the chicks’ died. Either disease or predation could theoretically explain the chicks’ high mortality rates, but that is probably not what happened, a scientist says.
The fence at the Vandenberg Air Force Base protects California least terns from human disturbance. Credit: Airman 1st Class Angelina Drake/U.S. Air Force
Dan Robinettte, an ornithologist at Point Blue Conservation Science, who has been collecting fecal pellets at the bird’s breeding colonies, is pretty sure that the chicks died of starvation or malnutrition. The adult birds, who deliver small fish one by one to their young, could not find enough 1-year-old Northern anchovy and young-of-the-year rockfishes to keep their chicks’ bellies full.
This does not mean we have overfished these fish species. Their abundances are linked to ocean cycles, as well as to fishing pressure. But, it is good reminder of how many animals, including seabirds, rely on the small fishes of the sea and why ecosystem-based management is important.
Read “Study: Seabird chick survival linked to diet.”