Young raccoon - Bill Buchanan/USFWS.

John Heinz National Wildlife Refuge at Tinicum provides critical habitat to a large variety of mammals. Some can be seen throughout the day while others may only leave behind signs of their presence like burrows, dens, or scat. The largest mammals found on the refuge are White-tailed deer (Odocoileus virginianus). A keystone species, the White-tailed deer is well documented throughout the state for its ability to alter habitats, consuming young trees that were destined to replace older trees in the canopy. 

Groundhog, Grey squirrel, Eastern cottontail, and muskrat are frequently observed. Rarely seen are some of the smallest mammals at the refuge: moles, voles, mice, and rats. Beaver, Long-tailed weasel, mink, and red fox are more elusive. Several species of bats also appear at dusk during warm summer months. Visit the refuge just after dawn or before sunset for the best opportunity to see these species.