Survival of captive-born cross-fostered juvenile Columbian ground squirrels in the field

Abstract

Effects of birth in captivity and cross-fostering of neonates on subsequent survival of female Columbian ground squirrels (Spermophilus columbianus) and their litters, after their immediate reintroduction into field sites, was evaluated for 116 litters over 2 years. Giving birth in captivity did not affect adversely survival of adult females to the following spring. Frequency of loss of entire litters was not greater for litters born in captivity than for those born in the field, and partial loss also appeared to be similar in the two groups based on litter sizes at emergence. Among captive-born litters, cross-fostering had no discernible adverse effect on juvenile survival relative to unmanipulated litters. Overall, fostered juvenues survived as well as non-fostered littermates to emergence and to the following spring, although in litters suffering partial loss, fostered juveniles had lower survival rates to emergence than non-fostered rearing mates. Of the elements of our protocol, only body weight of females significantly affected success in rearing the litter, and neither larger litters nor larger numbers of neonates fostered adversely affected success of the litter. Our results indicate that the protocol used is a robust method in situations requiring manipulation of litters or knowledge of litter size at birth.