Assessing effects of predation risk on foraging behavior of mule deer

We applied optimal foraging theory to test effects of habitat and predation risk on foraging behavior of mule deer (Odocoileus hemionus) subject to pr edation by mountain lions (Puma concolor). We predicted that deer would spe nd less time foraging, have higher giving-up densities of food (GUDs), and have higher vigilance behavior when occupying patch edges than when in open and forest interiors. We also measured GUDs in 3 microhabitats within 3 fo rest types. We used pellet-group surveys to estimate habitat and microhabit at use, and we assessed vigilance behavior with automatic camera systems. T he GUDs (perceived predation risk) were greater in forests of Douglas fir ( Pseudostuga menziensii) than mountain tain mahogany (Cercocarpus ledifolius ). In forests of Douglas fir, GUDs were greatest in the forest interior, de clined at the forest edge, and were lowest in the open microhabitat. Microh abitat features did not influence GUDs in the mountain mahogany forest. Pel let-group data indicated more activity in the open than in the edge or fore st. Based on photographs, deer were more vigilant at forest edges than in o pen and forest areas. We concluded that deer are responding to predation ri sk, by biasing their feeding efforts Ls at the scale of habitats and microh abitats and altering their habitat-specific patterns of vigilance behavior.