Sexual Segregation in Rocky Mountain Mule Deer

Abstract

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 10° more than males or coyotes(P 10°. Females were observed closer to water than males (P 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.