Population Ecology - Original Paper

Oecologia

, Volume 156, Issue 4, pp 773-781

Never too late? Consequences of late birthdate for mass and survival of bighorn lambs

  • Chiarastella FederAffiliated withDépartement de Biologie, Université de Sherbrooke
  • , Julien G. A. MartinAffiliated withDépartement de Biologie, Université de SherbrookeCentre d’Études Nordiques, Université Laval
  • , Marco Festa-BianchetAffiliated withDépartement de Biologie, Université de SherbrookeCentre d’Études Nordiques, Université Laval Email author 
  • , Céline BérubéAffiliated withDépartement de Biologie, Université de Sherbrooke
  • , Jon JorgensonAffiliated withFish and Wildlife Division, Department of Sustainable Development

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Abstract

In strongly seasonal environments, the timing of birth can have important fitness consequences. We investigated which factors affect parturition date and how birthdate interacts with sex, maternal characteristics and environmental variables to affect the growth and survival of bighorn sheep (Ovis canadensis) lambs in a marked population in Alberta. Over 14 years, the estimated birthdate of 216 lambs ranged from 21 May to 18 July. Parturition date was heritable and genetically correlated with maternal mass the previous fall. Weaning a lamb delayed parturition the following year by about 7 days. Birthdate did not affect summer growth rate, but late-born lambs were lighter in mid September (the approximate time of weaning) than early-born ones. Birthdate did not affect survival to weaning, but late birth decreased survival to 1 year for male lambs. Forage quality, measured by fecal crude protein, did not affect survival to 1 year. Once we accounted for lamb mass in mid September, birthdate no longer affected the probability of survival, suggesting that late birth decreased survival by shortening a lamb’s growing season. Because there was no compensatory summer growth, late-born lambs were smaller than early-born ones at the onset of winter. Our data highlight the importance of birthdate on life history traits and suggest that resource scarcity had more severe consequences for juvenile males than for females.

Keywords

Dimorphic species Sex Heritability Parturition date