We performed short-interval mark—recapture trapping on small mammals on Bumpkin Island in Boston Harbor in 2008, 2009, and 2011 in an attempt to record patterns of species distribution, population dynamics, and habitat use. The only species captured during these intervals were native Peromyscus leucopus (White-footed Mouse) and Microtus pennsylvanicus (Meadow Vole). Both mice and voles were trapped in 2008 and 2009, while only mice were trapped in 2011. Animal densities varied by vegetation type and by year. The variation in the densities between years may be attributed to a number of factors including food availability and the sporadic presence of predators, a unique characteristic of the some of the harbor islands.