CAN DISPERSAL BARRIERS REALLY BE USED TO DEPICT EMIGRATING SMALL MAMMALS

Small-mammal enclosure studies have attempted to depict emigrants as a nimals that are captured after they cross a barrier strip. These ''emi grants'' 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 th at did not cross the barrier. Forty-two of 45 animals that were captur ed greater than or equal to 7 times with greater than or equal to 2 ca ptures across the barrier strip had home ranges adjacent to the barrie r. These data suggest that most animals caught across the barrier were not emigrating but were making exploratory movements or had home rang es on the edge of the habitat. We question the use of dispersal barrie rs in depicting emigrants and recommend caution in interpreting result s from previous studies involving dispersal barriers.