Common raven movement and space use: influence of anthropogenic subsidies within greater sage‐grouse nesting habitat

Abstract

AbstractCommon raven (Corvus corax; hereafter “raven”) populations have increased dramatically in the western United States in recent years. Ravens benefit from human resources and are known predators of other avian species. We developed a raven study to determine how primary (large‐scale, high food density, and temporally consistent) anthropogenic subsidies influenced raven movement and space use during the raven and greater sage‐grouse (Centrocercus urophasianus) breeding season and within sagebrush habitat that is commonly used by greater sage‐grouse. We also examined how movement, space use, and anthropogenic subsidization differed among ravens in different breeding statuses. We hypothesized that breeding ravens would use small areas around their nest and that nonbreeding ravens would range widely in search of food. We expected that breeding ravens would frequently use anthropogenic structures and that both breeding and nonbreeding ravens would regularly visit primary point‐source subsidies (e.g., landfills and transfer stations). Twenty ravens were captured and GPS‐tagged between 2012 and 2014. We found that breeding ravens overwhelmingly built nests on anthropogenic structures (96–100%) and subsequently used small portions of the landscape intensively. Movement of nonbreeding ravens (distance average = 2783 m/h) and ravens who had failed nests (distance average = 1357 m/h) ranged widely. Breeding ravens visited highways and railroads inversely proportional to the distance between the nest and the nearest highway/railroad. Nonbreeding ravens regularly visited landfills and transfer stations, but breeding ravens did not (<0.1% of locations). We found that nonbreeding ravens travel widely to utilize primary point‐source subsidies, breeding ravens focus on areas near the nest, and ravens with failed nests switch to movement behaviors and space use similar to wide‐ranging nonbreeding ravens. These findings have implications for the management of ravens and anthropogenic subsidies in sagebrush landscapes to potentially reduce depredation of greater sage‐grouse nests.