Can dispersal barriers really be used to depict emigrating small mammals?

Abstract

Small-mammal enclosure studies have attempted to depict emigrants as animals that are captured after they cross a barrier strip. These "emigrants" are often categorized by age, sex, and reproductive condition. In a similar study with gray-tailed voles (Microtus canicaudus), we captured 307 of 1469 (21%) marked animals across a 1-m barrier strip. These animals consisted disproportionately of males and subadults, but did not differ in longevity or reproductive condition from animals that did not cross the barrier. Forty-two of 45 animals that were captured ≥ 7 times with ≥ 2 captures across the barrier strip had home ranges adjacent to the barrier. These data suggest that most animals caught across the barrier were not emigrating but were making exploratory movements or had home ranges on the edge of the habitat. We question the use of dispersal barriers in depicting emigrants and recommend caution in interpreting results from previous studies involving dispersal barriers.