Timing of breeding of pikas in southwestern Alberta.

Abstract

Conception dates of pikas were determined from the age of embryos in 125 collected females. First litters were conceived as early as would allow nursing under favorable feeding conditions. Mean birth date of first litters (June 8) coincided with the mean date of initiation of growth of vegetation (June 9). Second litters were conceived immediately after birth of first litters. Although pikas in southwestern Alberta matured later and conceived fewer litters per year than some other species of pikas, they matured earlier and conceived more litters per year than other subalpine and alpine mammals of similar size. This breeding pattern may, in part, be responsible for the success of pikas at high elevations.