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UBC Theses and Dissertations

Pregnancy rate and early lamb surviaval of California bighorn sheep (Ovis canadensis californiana, Douglas 1871) in the Ashnola watershed, British Columbia Harper, William Lamont


The Flatiron Mountain population of bighorn sheep [Ovis canadensis], with a history of low lamb recruitment, was studied to determine the timing of offspring losses, the nutritional and disease status of females, and the significance of suckling behaviour, weather, and predation on lamb survival. Pregnancy fate, determined by Doppler ultrasound diagnoses, was 100% in 10 adult females captured in mid to late gestation. Mortality of lambs belonging to tagged females was 64%, all occurring in the first month postpartum. Of the five females that were observable throughout the lambing period, three lost their offspring when the lamb was between five and 21 days old. Adult females from Flatiron Mountain were heavier and had higher body condition scores than a captive research herd with higher lamb production, suggesting energy status of Flatiron females was sufficient for lamb survival. Concentrations of selenium, copper, and zinc in the blood serum of Flatiron females in winter were marginally deficient, based on domestic sheep values. The one 9-month old lamb captured had very low levels of some blood minerals. Liver and kidney concentrations suggest that selenium in adult males was the only trace mineral marginally deficient in this population. The only important pathogen isolated from nasal swabs was parainfluenza type-3 virus, which was found in 50% of the 12 females sampled in late winter. Although several storms involving freezing temperatures and snowfall occurred during the lambing period, females with newborn lambs frequented lower elevations characterized by a milder microclimate, and there was no obvious correlation between inclement weather and periods of high lamb mortality. The suckling behaviour of Flatiron lambs was similar to that of other populations which, on average, had double the lamb production of Flatiron females. Analysis of predator scats, mainly coyote, revealed 24% by volume of their spring diet consisted of bighorn lambs. Based on the lack of significant nutritional, disease, or climatic factors, and considering the timing of lamb losses, coyote predation was hypothesized to be the most likely factor limiting lamb survival on Flatiron Mountain. Research effort should be directed towards testing this conclusion before management prescriptions are applied.

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