Survival of captive‐born Ovis canadensis in North American zoos

Abstract

The survival rate of North American bighorn sheep, Ovis canadensis, housed in several zoological gardens was analyzed. Complete herd histories, including birth and death data as well as causes of mortality, were collected from seven institutions. Lambs were divided into inbred and noninbred animals, with lambs being considered inbred if they had an inbreeding coefficient greater than zero. The rate of survival of inbred and noninbred lambs was compared using "survival equalling one year" and "survival equalling six months." Another analysis compared the survival rate of male and female inbred lambs and male and female noninbred lambs. Age at death was also compared in inbred and noninbred lambs. The analysis of the data for the seven collections, located in various geographic areas and housing various subspecies, indicates that inbreeding depression is a mortality factor in the captive management of North American bighorn sheep. Therefore, long-term survival of captive or isolated wild populations will depend on maintaining genetic diversity within the herds through careful selection of breeding stock in captive populations and introduction of nonrelated animals into isolated wild populations.

Inbreeding depression in captive bighorn sheep

“…The average inbreeding coefficient f for the inbred births is also given. The old records are the animals examined by Sausman (1984) In addition, we examined the effect of year of birth, place of birth, subspecies, sex and ancestral inbreeding upon viability. None of these variables had a strong or directional effect, or a statistically significant effect, upon viability, except that inbred sheep born in the early years of the study had significantly higher mortality than non-inbred ones.…”

“…As suggested by Gilpin & Soulé (1986), inbreeding depression and other factors reducing population numbers may interact and result in a greater decline than predicted from these factors individually. Sausman (1984) compared 6-month survival of 172 non-inbred and inbred bighorn sheep, captive-born in the 1970s and early 1980s. She found that survival of the non-inbred animals was 78% while that of the inbred animals was only 46%, suggesting that inbreeding depression was quite important in this species.…”

An investigation of inbreeding depression and purging in captive pedigreed populations

“…Inbreeding studies often concentrate on neonatal survival (e.g. Sausman, 1984;Lacy et al, 1993;Zschokke and Baur, 2002), presumably because it is an easily obtained measure of an individual's fitness. However, it may not necessarily be the fitness measure at which inbreeding depression is most strongly expressed.…”

Persistence of Different‐sized Populations: An Empirical Assessment of Rapid Extinctions in Bighorn Sheep

“…and etiological (Foreyt & Jessup 1982;Clark et al 1985;Wehausen et al 1987«) factors influence bighorn reproduction and survival, and, presumably, these affect persistence. In captivity, inbred bighorns suffer higher juvenile mortality than those from less inbred lines (Sausman 1984). Whether this occurs in field populations is unknown, but questions about population size and potential genetic effects can be examined because small founding populations are reintroduced (by wi\â-life managers) back into the same locations where native sheep become extinct (Leslie 1980;Gray 1986).…”