Alternative Maternal-Care Patterns in Two Herds of Bighorn Sheep

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Abstract
Suckling and related behaviors of Rocky Mountain bighorn sheep (Ovis canadensis canadensis) were studied on the National Bison Range, Montana (1983–1984), and in the Pecos Wilderness, New Mexico (1985). Lambs obtained 31–85% of suckles from alien females on the Bison Range, whereas no lambs suckled from alien females in the Pecos. Females appeared to invest equally in lambs in both herds, but additional nursing by helpers resulted in higher suckling rates for lambs on the Bison Range. Allomothers on the Bison Range were older and had more surviving offspring than other females in the herd. Allonursing was proposed as a response to high predation levels on the Bison Range.