California Least Tern

The California Least Tern is one of three least tern subspecies in North America, all of which are listed as endangered species under the Federal Endangered Species Act.
Found in California only during the breeding season—April to September—the California Least Tern spends the remaining parts of the year in southern latitudes. Although only here for half the year, these little birds put on quite a show.

The California Least Tern has an elaborate courtship display that is a necessary precursor to nesting. It begins with a male flying and calling with a fish in its beak. These males are then chased by a receptive female, undoubtedly impressed by the male’s fishing prowess. The chase is stupendous: spirited and swift, the terns weave high into the air and then hurtle towards the ground in unison. Back on the ground, the male will approach the female with the fish, strutting and dancing to impress. If the female accepts the advance, she’ll join in the dance. The female will eventually lay 1-3 cryptically colored eggs in a small depression: no nests are built, as the species relies on cryptic coloration and cooperation among colony members to help ward off potential predators. All the while, the male California Least Tern will feed the female while she incubates their eggs.

Unfortunately for the California Least Tern, the very areas it needs to nest are also highly sought-after by humans for development and recreation. The species needs expansive stretches of shoreline near abundant supplies of prey—primarily small, nearshore fish—to survive and flourish. Historically, these areas were abundant, and the species could be found in great numbers from Moss Landing, Monterey County, California to San Jose del Cabo, southern Baja California, Mexico. But growing development and recreational pressures have destroyed habitat, disturbed birds, and increased predation by introduced and native species. The construction of the Pacific Coast Highway brought all these threats to much of California’s coast, and by the 1940s, terns were gone from most beaches of Orange and Los Angeles counties and were considered rare elsewhere.

To avoid humans, some tern colonies nest at more inland mudflat and dredge fill sites, which appears to make them more susceptible to predation by foxes, raccoons, cats and dogs. Indeed, some biologists believe that the Bay Area’s sole nesting population—which is outside the historic range noted for the species—was created by forced expansion of birds from the south that were pressured out of their original habitats.