An important study released today concludes that the presence of cattle in important sage grouse habitats increases the number of ravens that prey on sage grouse and their nests by 45.8% in the Curlew Valley of southeast Idaho. The study found that anthropogenic subsidies were increased in areas where livestock grazing occurred and raven populations increased as a result. The increased numbers of ravens selected areas close to active sage grouse leks (breeding areas) which are correlated to areas where sage grouse choose their nests.
Anthropogenic subsidies from livestock grazing can include carcasses of cattle, feed grain, dung, insects in dung, water from livestock water troughs, perching structures that make it easier for ravens to see their prey, and nesting structures.
Previous studies have shown that, areas where grazing reduces grass and forb cover which are important for nesting and brood rearing cover, the ability of ravens and other predators to locate nests and chicks increases. Raven populations have also been implicated in the reduction of reproductive success of sage grouse. Cattle can also disturb sage grouse nests and flush the hens letting the ever observant ravens locate nests. Previous studies on sage grouse predation have documented ravens as one of the most frequent predators to sage grouse nests. These studies also documented that cattle actually eat sage grouse eggs right from the nest.
The paper suggests that limiting anthropogenic subsidies and segregating livestock from sage grouse breeding areas is likely to reduce raven predation of sage grouse eggs.
Here is the USGS press release: Cattle Increase Occurrence of Ravens That Prey on Sage Grouse (3/2/2016 10:00:00 AM)
Coates P. S., B. E. Brussee, K. B. Howe, K. B. Gustafson, M. L. Casazza, and D. J. Delehanty. 2016. Landscape characteristics and livestock presence influence common ravens: relevance to greater sage-grouse conservation. Ecosphere 7(2):e01203. 10.1002/ecs2.1203