Vertebrate Pest Conference Proceedings collection


Date of this Version

March 1992


Several small nesting colonies of the endangered California least tern (Sterna antillarum browni) remain along the California coast. The largest of these is located on Camp Pendleton Marine Base in southern California. Many forms of disturbance have apparently contributed to the decline of this tern species, including corvid, primarily raven (Corvus corax), predation on the eggs. Efforts to eliminate corvid predation have primarily focused on shooting offending birds; this method is selective, but it has inherent public safety problems. In 1988, biologists from the Denver Wildlife Research Center (DWRC) and the U.S. Navy, in cooperation with USD A Animal Damage Control personnel, conducted a pilot study at Camp Pendleton to determine if corvids could be selectively removed by consuming hard-boiled chicken eggs treated with the avicide DRC- 1339. Thirty-six treated eggs, 6 per clutch, were exposed in dummy ground nests in raven nesting territories in the vicinity of one of the tern colonies. Egg baits were readily consumed by ravens, but several others were cached. After selectively removing only three to four ravens with this method, the least tern fledging rate for 1988 at Camp Pendleton was the highest in recent years.