Sexual segregation in Rocky Mountain mule deer

Two leading explanations for sexual segregation in polygynous ungulates include the reproductive-strategy and the sexual dimorphism-body size hypotheses. We tested predictions of these hypotheses by comparing habitat use, characteristics of feeding sites, diet composition, and diet quality between male and female mule deer (Odocoileus hemionus hemionus) at Hart Mountain National Antelope Refuge (HMNAR) in southeastern Oregon. Females selected ''mesic'' and bitterbrush cover types (P < 0.01) and males selected primarily mountain big sagebrush communities (P < 0.01). Females used slopes >10 degrees more than males or coyotes(P < 0.01), particularly during and immediately after parturition (Jun-Jul), which may have increased security for fawns because coyotes were rarely observed on slopes >10 degrees. Females were observed closer to water than males (P < 0.01), and used feeding sites with greater shrub canopy cover (P < 0.01), hiding-cover above 0.5 m (P < 0.01), and shrub species richness (P < 0.01) than feeding sites of males. Feeding sites of males had greater biomass (P < 0.01) and species richness of forbs (P < 0.01) than feeding sites of females. Forage class composition of male and female diets did not differ (P = 0.99) and consisted primarily of forbs (>75%). Concentrations of diaminopimelic acid (DAPA), an index of diet quality, were higher in fecal samples of males than females (P < 0.01). Our data supported predictions of the reproductive-strategy hypothesis that sexual segregation occurred as the result of different strategies by males and females to enhance reproductive fitness. Females used areas of low coyote activity, high security benefits, palatable browse resources, and proximity to water, all of which are likely to increase offspring survival. Males used areas that maximized foraging opportunities for preferred diet items. Because males foraged in areas with greater biomass and species richness of forbs and obtained a higher-quality diet than females, we rejected the sexual dimorphism-body size hypothesis that predicts males would segregate to areas of more abundant, lower-quality forage.