Raccoon distribution and land cover associations on a barrier island complex

Background/Question/Methods: The raccoon (Procyon lotor) is a major predator on beach-nesting and colonial waterbirds on the U.S. Atlantic and Gulf Coasts. This study investigated the dual influences of land cover composition and island accessibility on raccoon distribution and abundance on 31 island and marsh surfaces along the seaward margin of the southern Delmarva Peninsula and how changes in land cover over an 18-year period impacted them. Eleven islands previously were classified as resident/source islands and 20 as transient/sink islands. We harnessed ecological data from 11 years of USDA-WS raccoon trapping data (1,396 captures) on 11 islands and combined it with high-resolution (30-m pixel) NOAA C-CAP land cover maps for the year 2010 to determine the cover-class associations for each of 7,210 trap stations. Eleven cover classes were represented. We tallied the area for each cover found each surface. Based on capture data, station GPS locations and cover-class information, we calculated the observed capture rate for each cover class, and estimated land cover suitability (proportion of a land cover times its capture rate, summed for each surface). We then calculated the projected numbers of captures based on cover class areas and land-cover-specific capture rates for each surface. Land cover suitability and projected number of captures were recalculated using a 1992 land cover layer to examine what effect land cover changes might have had on raccoon distribution or abundance.

Results/Conclusions: The rate of raccoon capture differed between land cover categories (Χ²=285, df=11, p<0.001), with bare land and grassland having exceptionally low rates and higher rates in woody land covers, particularly evergreen forest. Surfaces previously designated as raccoon sources and sinks differed in their land cover suitability and projected number of captures (H=5.35, df=1, p <0.02 and H=14.11, df=1, p<0.001 ), with source islands having higher values on both measures. Analysis of the land cover changes on each surface between 1992 and 2010 found that land cover suitability (r_s = 0.868, p<0.001) and projected number of captures (r_s = 0.975, p<0.001) for each surface were highly correlated across years. These results have implications for management by targeting removal trapping of raccoons to protect shorebird nesting areas in land cover types with the highest rates of captures, and in the assessment of novel surfaces as potential sources of raccoons.