Sexual segregation in white-tailed deer: Density-dependent changes in use of space, habitat selection, and dietary niche

Abstract

Sexual segregation, defined as the exclusive use of different areas by males and females at specified spatial and temporal scales, is common among polygynous ruminants and in cervids in particular. Underlying mechanisms for such segregation are not understood fully, and reports have included female cervids segregating into habitats of both poorer and better quality than those used by males. Furthermore, two competing hypotheses of sexual segregation (body-size hypothesis, reproductive-strategy hypothesis) predict different responses to changes in population density; an increase in degree of sexual segregation with increasing density in the former and a decrease in segregation in the latter. We examined patterns of sexual segregation among white-tailed deer (Odocoileus virginianus) on the Welder Wildlife Refuge in south Texas at moderate (39 deer/km2) and high (77 deer/km2) population densities during 1974-1977. At moderate density, females with young made greater use of chaparral-mixed grass habitat with dense cover than did males, where preferred herbaceous forage was less abundant, presumably for reasons of predator avoidance. At high density, which was a result of predator control, sexual segregation among male and females decreased during all seasons (P < 0.05). Males that otherwise used more open habitats increased their use of the chaparral-mixed grass as levels of intraspecific competition increased. As spatial segregation between males and females decreased at the high population density, diets of both sexes shifted toward more graminoids and browse, and shifts were more pronounced among males. The result was decreased dietary overlap between sexes when measured by principal-component analysis. Measures of fat reserves suggested that although both females and males were in poorer condition at high density, females were affected to a greater extent than were males. This outcome suggested that females were not driving patterns of spatial segregation by being better able to compete with males for closely-cropped forages. Rather, predator avoidance by females with young related to the reproductive-strategy hypothesis best explained patterns we observed, and competition between sexes was rejected as a cause of sexual segregation.