Northern Prairie Wildlife Research Center
MICHAEL D. SILBERNAGLE, RICHARD ZEMBAL, AND
ESTHER E. BURKETT
U.S. Fish and Wildlife Service, Kern National Wildlife Refuge, P.0.
670, Delano, CA 93216-0670; U.S. Fish and Wildlife Service, Ecological
Services Division, 2400 Avila Road, Laguna Niguel, CA 92677; California
Department of Fish and Game, 11862 MacGill Street, Garden Grove,
Electric fencing has been used to protect terns from mammalian predators on the Refuge since 1979, with varying degrees of success. Fencing was adjusted when mammalian predators breached the existing design. The latest design is a 1.5-m electric fence backed with 2.5-cm mesh poultry netting and deterrents (to prevent jumping over or digging under). Fledgling success at this site has increased from < 0. 8 fledglings per adult pair to > 1.1 fledgling per adult pair and percentage of nests depredated has declined from >70% to <1% between 1988 and 1989. Avian predators have been successfully deterred from this site through the use of anti-perching materials such as Nixalite. However, no fence design was totally effective in preventing mammalian predator access. High maintenance requirements because of the moist, saline coastal environment caused equipment and materials to fail, and some predators were able to overcome all deterrents.
Protecting the light-footed clapper rail from predation has proved more difficult. We have constructed earthen mounds and floating wooden rafts away from the marsh edge to provide nesting sites less susceptible to predation. These efforts failed to reduce clapper rail losses. Nocturnal spotlight surveys at the Refuge and surrounding Naval Weapons Station indicated abnormally high numbers (=59.5 per survey) of a non-native predator, the red fox.
When other efforts to protect California least terns and light-footed clapper rails failed by July 1986, we began a trapping program to remove red foxes from about 2,000 ha of the Refuge and the surrounding Navel Weapons Station lands. From 1996 to 1990, 275 red foxes were trapped using padded leghold traps and removed. California least tern fledgling success ranged from about 1.2 to 1.9 fledglings per adult pair since 1986, when electric fencing was combined with predator removal. An exception was in 1988 when a red fox breached the fence and 71 % of the nests present were depredated that year; about 0. 8 fledglings per adult pair were produced.
An animal rights group filed suit in 1986 to halt the trapping program, but the government's position prevailed. On appeal, in June 1988, the 9th Circuit Court overturned the decision. The case was remanded back to District Court and the government was ordered to prepare an Environmental Impact Statement (EIS). This document, covering endangered species management and protection at the Refuge, is in preparation and scheduled to be completed by September 1990.