Vertebrate Pest Conference Proceedings collection

 

Date of this Version

March 1978

Abstract

A limited study on two ranches near Dillon, Montana, near the end of the lambing season in 1974 revealed that 44 domestic lambs were killed by golden eagles (Aquila chrysaetos). This was 76 percent of all deaths recorded during the short study. Using an average docking percent of 90 (based on years before severe eagle problems developed), the 76 percent eagle predation, and the 1974 docking percentages, the ranchers estimated an eagle kill of 1,092 lambs valued at about $38,000. The U.S. Fish and Wildlife Service live-trapped and removed 249 golden eagles from the ranches during the next three springs. During 1975, when 145 eagles were removed, docking percentages were even lower than in 1974, and the ranchers estimated a loss of $48,000. During 6 hours on one ranch in 1975, I found 15 fresh eagle kills. Less severe eagle problems occurred during 1976 and 1977, and the docking percent-ages improved. The effect of the trapping program on predation could not be evaluated. Lamb losses were greatest during the years of greatest trapping success. Decreasing lamb losses in 1976 and 1977 may have resulted from increasing populations of jackrabbits (Lepus spp.) throughout the West. Juvenile and subadult golden eagles caused most of the predation. A decline of jackrabbits may have caused these young birds, which had no established territories, to concentrate on the lambing grounds. As numbers of sheep decline on western ranches, eagles may take a greater percentage of lambs from the remaining herds. With golden eagles totally protected, increasing predation on lambs should be expected, especially when natural prey is scarce. Because of the expense and the relative scarcity of qualified personnel, the trapping and moving of depredating eagles is not a practical operational procedure. Non-lethal methods of eagle management show little promise for alleviating lamb losses. Experiments should be conducted combining scare tactics, including shooting near the birds, with limited killing for reinforcement. Illegal control may endanger juvenile bald eagles (Haliaetus leucocephalus) and result in the killing of many golden eagles if ranchers are not assured of aid when a serious depredation problem occurs.