Ecological Predictors of Habitat Occupancy for the Southeastern Beach Mouse

Abstract The federally threatened southeastern beach mouse Peromyscus polionotus niveiventris occupies just a fraction of its former range along Florida’s Atlantic coast, mostly within the 72 km of continuous coastline on federal lands of the Cape Canaveral Barrier Island Complex. Although believed to be caused by loss and degradation of habitat associated with human urban expansion, no precise explanation for the reduction in southeastern beach mouse range is known. We used nine years of winter habitat occupancy survey data for a trend analysis, and a subset of four years to identify key factors influencing occupancy dynamics in coastal habitat throughout the core population. Using a maximum likelihood based model selection approach, we tested evidence for the effects of environmental and anthropogenic factors arranged into four hypotheses related to habitat structure, beach erosion, population isolation, and access to inland habitat. As predicted, sites closer to the primary dune, farther from open water, and with higher elevation had higher initial occupancy than sites with the opposite characteristics. Also as predicted, sites farther from open water, with higher elevation, more coastal strand, less ruderal vegetation, and in proximity to oak trees had lower site extinction. Contrary to predictions sites closer to infrastructure (roads, railroads, paved sites) and more isolated by narrow width or unsuitable habitat features also had lower extinction, possibly because of restriction of predator access. A Bayesian analysis showed that annual southeastern beach mouse habitat occupancy was generally high (0.63–0.97) but variable across the 72 km of coastal dune spanning most of the remaining species’ range. Simulation showed that the power of the survey was sufficient to detect a 20% decline between years. This study provides a baseline of knowledge about habitat occupancy dynamics for future monitoring and management of the southeastern beach mouse and other beach mouse subspecies.