Frequency of Birth and Lambing Sites of a Small Population of Mountain Sheep

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The Southwestern Naturalist



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We examined frequency of lambing, lamb survivorship, site fidelity for lambing areas, and described lambing areas of a small population of mountain sheep (Ovis canadensis mexicana) in the Little Harquahala Mountains, Arizona from 1989 to 1991. We collected data from 57% of the population by radio-collaring 10 adult females and two lambs, and relocated the females during and after parturition each year (266 relocations). Nineteen lambs were born to 10 females. Six of these lambs survived ≥6 months and 13 lambs lived an average of 34 days. One lamb died from a fall and one died from being stepped on; the causes of the other 11 mortalities are unknown. Five females did not raise any lambs that lived ≥6 months in any year. No female raised a lamb that lived ≥6 months in 2 consecutive years. Lambing areas used by individual females were separated by more than 7 km each year. No female used a lambing area used by another female. Percent slope, topographic position, and vegetation composition were not different at lambing sites compared to sites used during other times of the year. Habitat used by females during the period around parturition had more thermal cover than random sites. Habitat used by female sheep throughout the year was steeper, higher in topographic position, and had more brittle bush {Encelia farinosa), creosote bush {Larrea tridentata), palo verde (Cercidium microphyllum), and barrel cacti (Ferocactus wislizenii) than random sites. Lambing sites are used for relatively short periods of time and their importance may be underestimated by broad scale studies of habitat use.

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