Population ecology of Columbian ground squirrels in southwestern Alberta

Abstract

The characteristics of a large population of Columbian ground squirrels (Spermophilus columbianus), the numbers of which varied between ca. 700 and 1000 animals emerging in the spring, were studied over a 7-year period in southwestern Alberta. Over time, the density of nonjuvenile squirrels varied between 11.6 and 16.1/ha, with a sex ratio that consistently favoured females; the density of juveniles varied between 4.6 and 20.7/ha, but with a sex ratio that was usually balanced. Spatially, the density of squirrels also varied with a certain part of the study area (17%) annually supporting proportionately more animals of each sex than the remaining 83%. Dispersal was recorded primarily among yearlings, with more males than females involved in this movement. Most dispersal occurred in late June and early July, centred on the time juveniles emerged from natal burrows. We recorded squirrels dispersing up to 6.7 km. Survival of squirrels in their 1st year of life was lower (females 40%; males 35%) than in any subsequent year (females 50–64%; males 37–54%). These attributes of Columbian ground squirrels are compared with those of other members of the genus, and the evidence they provide for population regulation is discussed.