Factors controlling lambing period of Dall's sheep

Abstract

Distribution of birth dates within the study population of Ovis dalli dalli reveal two distinct oestrous cycles with a further 15% of all births resulting from a third cycle. The onset of breeding appears governed by photoperiod. Lambs born early and late in the lambing period suffer higher mortality. Energetic constraints limit both onset and duration of lambing. Onset is delayed beyond the period critical to thermoregulation by lambs and until forage is adequate; duration is limited by the need of lambs to attain adequate body size by winter.