Variation in winter microclimate and its potential influence on Virginia opossum (Didelphis virginiana) survival in Amherst, Massachusetts

If climate limits the geographical distribution of a species, local variation in microclimate may affect the species' local distribution at the edge of its range. We hypothesized that warm urban microclimates may explain the distribution of the Virginia opossum (Didelphis virginiana) in central Massachusetts. We recorded winter temperatures with data-logging sensors in urban, coniferous, deciduous, and open habitats in the human-dominated landscape of the Connecticut River Valley of Massachusetts. Overall, temperatures decreased with elevation. Daily maximum temperatures, a variable used in models of opossum biophysical constraints, were lowest at forested sites, intermediate at urban sites, and highest at open sites; however these were a poor indicator of evening temperatures, which are important to the nocturnal opossum. Open sites had the highest daily temperature fluctuations, and were the coldest at night. Urban and coniferous sites had the least pronounced daily fluctuations in temperature, and urban sites had the warmest nights. Habitat-specific winter temperatures in the Connecticut River Valley indicated that urban sites were most conducive to opossum persistence, but even they were unlikely to sustain populations. Other factors likely help mitigate the influence of harsh climatic conditions on persistence of opossum populations in western Massachusetts. © 2005 Springer Science + Business Media, Inc.