Date of Award
9-2-1994
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biology
Abstract
This study examines reproductive patterns of two herds of bighorn sheep (Ovis canadensis) in contrasting and extreme environments, to look at the range of variability that exists in certain reproductive traits. Desert bighorn sheep (O. c. nelsoni) were studied in the River Mountains of Nevada, an area characterized by hot, dry summers and mild winters. Rocky Mountain bighorn sheep (O. c. canadensis) were studied in the Pecos Wilderness of New Mexico, an area characterized by cool, wet summers and cold, snowy winters. The objective of the study was to determine lamb production and survival, lamb birth dates, and postnatal maternal investment for individually recognizable bighorn sheep in each population. Field work began during June 1989 and terminated during August 1992.I recognized 60 ewes in the River Mountains, and 113 ewes in the Pecos Wilderness. Lambing seasons were exclusive in the two areas. Lambing peaked during February and March in the River Mountains, and during mid-June in the Pecos Wilderness. Year-to-year differences were apparent in the River Mountains, but not in the Pecos Wilderness. The effects of temperature and nutrition as both proximate and ultimate regulators of the lambing season are discussed.Lamb production varied with maternal age, and was similar in both herds. Lamb survival did not differ with maternal age, but differed between herds and among years. In both populations, lamb survival varied with winter precipitation but in different ways. Heavy precipitation increased lamb survival in the River Mountains, but decreased it in the Pecos Wilderness.Birth sex ratios were male biased in both populations, with no maternal age effects. Interbirth intervals were longer after the rearing of female than male lambs in the River Mountains, but not in the Pecos Wilderness. Nursing behavior did not differ between herds or between lamb sexes in either herd. Nursing frequencies and rates increased with ewe age in the Pecos Wilderness, but not in the River Mountains. Nursing behavior appeared sensitive to diet quality during late gestation and early lactation.
Recommended Citation
Hass, Christine C., "Reproductive ecology of bighorn sheep in Alpine and desert environments." (1994). Theses and Dissertations. 8772.
https://commons.und.edu/theses/8772