U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version

February 2004


Published in Canadian Journal of Zoology, Vol. 82 (2004), pp. 1837-1842.


From 1997 to 2001, we monitored movements of 109 adult and 114 juvenile swift foxes, Vulpes velox (Say, 1823), at study sites in Colorado, New Mexico, and Texas to determine patterns of dispersal. Significantly more male (93%) than female (58%) juveniles dispersed, and both sexes had similar bimodal dispersal patterns with peaks in September–October and January–February. Adult dispersal occurred more evenly throughout the year, and significantly more male (32%) than female (5%) adults dispersed. Adult males tended to disperse after the death of their mate. Of dispersing foxes with known fates, settlement percentages in new territories were similar between juvenile males and females (40% overall), but they were significantly lower than for adults (89%). All other dispersing foxes with known fates died. Among juvenile females with known fates, similar percentages of philopatric and dispersing foxes reproduced as yearlings (50% overall), so the benefits of dispersal versus philopatry were not clear. Although rarely reported for other species, adult males were an important dispersal cohort in swift foxes (43% of male dispersals and 25% of all dispersals). Because of the female-biased philopatry among swift foxes, dispersal of adult males likely decreased the chances for inbreeding (e.g., father–daughter breeding).