Intercolony natal dispersal in the Columbian ground squirrel

Abstract

Dispersal of Columbian ground squirrels (Spermophilus columbianus) among 16 colonies located in the Sheep River – Gorge Creek drainage of southwestern Alberta was studied from 1973 to 1986. In total, 73 intercolony movements involving 66 different animals were recorded. Intercolony dispersal movements were strongly biased towards males and were almost exclusively undertaken by 1-year-old squirrels (yearlings). The timing of emigration from the colonies studied was highly synchronous and was correlated with the dates of emergence of new litters. Yearling females that dispersed tended to leave at a later date than did yearling males. Most (91%) animals that dispersed moved to colonies <4 km away but movements of up to 8.5 km were recorded. There was no difference in median distance dispersed for male and female yearlings (2.0 and 1.8 km, respectively). Dispersing squirrels departed from colonies in nonrandom directions apparently following such features as trails and drainage systems. Such movement seemed to enhance the squirrels' chances of successfully locating nearby colonies. Minimum known survival rates while in transit for yearlings were 16% for males and 11% for females. Estimates of actual survival in transit for yearlings were 26% for males and 30% for females.