Do reproductive status and lamb gender affect the foraging behavior of bighorn ewes?

In female ungulates lactation carries a high energetic cost and mothers oft en devote more care to sons than to daughters. The aims of this study were to determine whether lactating bighorn ewes have higher foraging time, bite rate or selectivity of forage than barren ewes and whether reproductive st atus affects migration patterns. Ewes with male lambs were predicted to spe nd more time foraging and to have a higher bite rate than ewes with female lambs. There were no differences in foraging behavior according to ewe repr oductive status from April to August. In September-November lactating ewes had a higher bite rate and spent more time foraging than nonlactating ewes but lamb gender did not affect foraging behavior. Lactating ewes gained les s weight than nonlactating ones until mid-August; from mid-August to late S eptember mass gain was similar for both groups of ewes. Nonlactating ewes s pent more time standing but reproductive status did not affect vigilance be havior or step rate while foraging. Ewes with lambs did not differ from non lactating ewes in step rate. Pregnant ewes migrated earlier than barren ewe s to alpine areas in spring. By so doing they abandoned areas with good qua lity forage presumably to give birth in areas safer from predation. All ewe s spent most of the summer in the alpine range but nonlactating ewes return ed to the winter range earlier than lactating ewes, probably to profit from the abundant forage there.