Response of Great Horned Owls to Experimental "Hot Spots" of Snowshoe Hare Density

Rohner, C; Krebs, C

Predators that aggregate in "hot spots" of high prey density have been hypothesized to synchronize population cycles of small mammals. During a peak and decline in a snowshoe hare (Lepus americanus) cycle, we created artificial hot spots of increased hare abundance by adding food and excluding mammalian predators on three blocks and then recorded the response of radio-marked Great Horned Owls (Bubo virginianus) to these food additions. Territorial owls showed a decrease in home range size and patchiness of spatial use as hare densities peaked and declined, although this was better explained by smaller territory sizes due to a growing owl population rather than a direct behavioral response to changing food density. Experimental owls on food-enriched territories did not show a difference in conventional measurements of home-range size and patchiness of spatial use compared with controls, but the distances of owl locations to treatment blocks revealed concentrations of spatial use on experimental hot spots. At a larger scale, neither territorial owls nor nonterritorial floaters showed a tendency to leave poorer patches and move toward hot spots, and the territorial system of Great Horned Owls was largely resistant to extreme variations in prey density. The effect of social interference between predators has been assumed for several models of predator-prey interactions, but empirical evidence has rarely been demonstrated. Our results suggest that territorial behavior, in addition to limiting the growth of a predator population, also prevents large aggregations of predators at an intermediate spatial scale.

Response of Great Horned Owls to Experimental "Hot Spots" of Snowshoe Hare Density

Series