Predators, Predator Removal, and Sage-Grouse: A Review

Populations of greater sage-grouse (Centrocercus urophasianus; sage-grouse) have been in a decline since the nineteenth century. We used our research, unpublished reports, and scientific literature to identify which predators kill sage-grouse and to assess whether lethal control of these predators benefited the species. We also asked state wildlife biologists and scientists whether they had ever witnessed a predator kill sage-grouse. We identified 266 instances where the predator responsible for depredating nests or killing juvenile or adult sage-grouse could be ascertained. Most adult sage-grouse were killed by eagles (Accipitridae), owls (Strigiformes), coyotes (Canis latrans), or red foxes (Vuples vulpes). Based on nest cameras, most depredated eggs are taken by common ravens (Corvus corax), badgers (Taxidae taxus), or coyotes. There are too few studies to conclude that predator removal increases survival rates of juvenile or adult sage-grouse. No study has been conducted to determine whether badger removal increases nest success of sage-grouse, and the only study on coyote removal produced ambiguous results. Several studies reported that more sage-grouse nests are successful (i.e., >1 eggs hatched) in areas where common ravens were removed or in areas where raven densities were lower than in other areas. The data we reviewed did not indicate predators played a role in the decline during the past century, but increasing numbers of ravens since the 1970s may have contributed to the declining sage-grouse populations in recent decades. We conclude that removing common ravens can increase nest success, although not necessarily sage-grouse abundance. Without a better understanding of sage-grouse and their predators, wildlife biologists will be handicapped in their efforts to prevent sage-grouse populations from continuing to decline.