The Least Tern is regrded by many as a separate species to Little Tern. Photo: S Maslowski (USFWS)

At San Diego Bay National Wildlife Refuge, in California, there is one of only two breeding sites of Gull-billed Tern (subspecies Gelochelidon nilotica vanrossemi) in the western United States.

The adult terns are known to prey on western Snowy Plovers and the California Least Terns, both listed as Endangered species. Because of this, the US Fish and Wildlife Service proposes to control the tern population by destroying their eggs.

The numbers involved are not that large - in San Diego Bay there are about 50 pairs of Gull-billed Terns, 80 pairs of Least Terns, and 2 pairs of Snowy Plovers. However, the foraging range of the Gull-billed Terns is wide and includes other more distant colonies of Least Terns and nesting areas of Snowy Plovers.

The Gull-billed Tern is regarded as a California Bird Species of Special Concern and for the Fish and Wildlife Service, the problem is how to prevent predation of the two rarer species. They have decided to use corn oil to coat some of the tern eggs to prevent them hatching and have calculated that if 43 percent of the eggs are prevented from hatching this will reduce predation while not affecting the tern population.

But not everyone is in favour of this drastic solution. Some critics claim that habitat loss, human recreational disturbance, and wildlife predation from feral cats and wild predators, are more important considerations than Gull-billed Tern predation.

According to Audubon California: “In a perfect world, there would be enough breeding and foraging habitat for each of these species to prosper. Before anyone sacrifices a population of a sensitive species to save other threatened or endangered species, it only makes sense to get all the relevant information on the table and have all concerned parties come up with a science-based solution that is the best for the birds.”

The Center for Biological Diversity said conservation biologist Tierra Curry.:  “In the United States and Mexico, there are roughly 1,000 to 2,000 western Gull-billed Terns, 5,000 Snowy Plovers, and 14,000 California Least Terns. On the Bay Refuge, there are roughly 100 adult gull-billed terns, four adult plovers, and 160 adult least terns.

“We acknowledge the impact of predation on the refuge; the real problem for the plover and both the tern species, however, is habitat destruction. It is the job of Fish and Wildlife Service to protect this rare tern, not to push it closer to extinction.”

See the draft Environmental Assessment on managing the Gull-billed Terns at San Diego Bay