Friday, August 6, 2010

PS 97-71: Mammalian carnivore declines on a mid-Atlantic peninsula

Aaron S. Hogue, Salisbury University


The Delmarva Peninsula is located along the mid-Atlantic coast of the US, forming the eastern border of the nation’s largest estuary, the Chesapeake Bay. Fur trade records from 1695 indicate that it was once home to a rich diversity of mammalian carnivores (carnivorans), including raccoon, mink, fox (likely native gray and introduced red fox), North American river otter, wildcat (likely bobcat), and black bear. Additional evidence indicates striped skunk, long-tailed weasel, red wolf, and cougar were also likely present. However, a combination of intensive early colonial trapping, persecution, lax post-colonial trapping regulations, habitat loss, and habitat fragmentation appear to have led to significant declines in this diversity. Of the 10 native carnivorans formerly residing on the peninsula, three are known to be extirpated (cougar, red wolf, black bear) and three others remain in question (bobcat, mink, long-tailed weasel). The aim of this study was to use infrared game cameras, track boxes, and mink rafts to inventory carnivoran populations on the central portion of the peninsula and identify existing populations of the three species in question.


A total of 58 camera stations and 30 mink raft sites were operated in four central Delmarva counties over a 9 month period for a total of 902 camera days and 402 mink raft days. In addition to several avian species, 13 wild mammal species were documented (listed in order of frequency): opossum, raccoon, white-tailed deer, gray squirrel, gray fox, eastern cotton tail rabbit, red fox, sitka deer, flying squirrel, ground hog, and skunk. Incidental records were also obtained for two additional species: coyote and North American river otter. Thus, of the 10 native carnivorans historically present in the region, only four were found in this study.  Two additional introduced or invasive carnivorans were also documented. Given the importance of carnivorans in regulating prey populations, the possible loss of over half the native species in this region is particularly troubling. Future work should expand survey efforts to additional sites on the peninsula and potentially include more costly, more effective survey techniques to ensure small isolated populations of the three target species do not escape detection.