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1、Gap-Crossing Decisions by Red Squirrels in Fragmented Forests Victoria J. Bakker, University of California, Davis Rationale Knowing how mammals move in fragmented forests can aid in location of reserves and corridors. Questions exist about which factors control decisions of mammals to cross gaps in
2、their preferred habitats. Objective To study factors for decisions by red squirrels (Tamiasciurus hudsonicus) to cross gaps in fragmented forests. Forest-clearcut edge at central Mitkof Island study site, Tongass National Forest, Alaska. Logging is the primary land use. Translocation of individual s
3、quirrels across gaps for release and subsequent tracking. Hypotheses Efforts to minimize predation risk, en- ergy expenditures, or encounters with territorial conspecifics were hypoth- esized to control crossing decisions. Predation risk was assumed higher in clearcuts than in forests because of low
4、er overstory cover and lack of trees for escape. Energy expended per distance trav- eled was assumed higher in clearcuts due to higher shrub stem densities. Conspecific encounter rates were lower in clearcuts than forests. Methods Documented home ranges and terri- torial behaviors of squirrels livin
5、g near clearcuts less than 10 years old. Induced movement by translocating individuals across gaps. Used radio-telemetry to document homing paths. Conducted call-back surveys along clearcut perimeters to determine con- specific defense levels. Used logistic regression to relate ex- trinsic factors,
6、such as gap size, and intrinsic factors, such as body mass, to gap crossing probability. Results and Discussion Of 30 squirrels translocated at 5 clearcuts, 11 crossed clearcuts and 19 detoured along forested routes. Gap crossing probability was in- versely related to squirrel body mass and detour e
7、fficiency (D): Lighter squirrels were more likely to cross clearcuts. Squirrels in poor condi- tion may take more risks when moving. Squirrels were more likely to cross if detours were long, suggesting that squirrels assess distances of detours and that predation risk, energetics, or both influence
8、crossing decisions. Squirrels choosing forested routes avoided the route with the greatest number of highly defended territories. Non-significant factors were crossing distance, clearcut size, clearcut age, and individuals territorial behavior. Determinants of gap-crossing: Relationship be- tween detour efficiency, body mass, and gap-cross- ing probability, based on logistic regression. Acknowledgments: U.S. Environmental Protection Agency Office of Research and Development home distanceIndirect home distanceDirect = = = = D
