The cost of dispersal: predation as a function of movement and site familiarity in ruffed grouse

Ecologists often assume that dispersing individuals experienceincreased predation risk owing to increased exposure to predatorswhile moving. To test the hypothesis that predation risk isa function of movement distance or rate of movement, we usedradio-telemetry data collected from 193 ruffed grouse (Bonasaumbellus) during 1996–1999 in southeastern Ohio. Cox'sproportional hazards model was used to examine whether the riskof predation was affected by the rate of movement and site familiarity.We found evidence indicating that increased movement rates mayincrease the risk of predation for adult birds but not juveniles.We also found juvenile and adult birds inhabiting unfamiliarspace were consistently at a much higher risk of predation (threeto 7.5 times greater) than those in familiar space. Our resultsindicate that although movement itself may have some effecton the risk of being preyed upon, moving through unfamiliarspace has a much greater effect on risk for ruffed grouse. Thissupports the hypothesis that increased predation risk may bean important cost of dispersal for birds.