Sexual Segregation in Southern Mule Deer

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Abstract
Sexual segregation in southern mule deer (Odocoileus hemionus fuliginatus) was studied on East Mesa, Cuyamaca Rancho State Park, San Diego Co., California, from June 1977– January 1979. Spatial separation of the sexes occurred throughout the dry portion of the year (May–October), but was most pronounced during and immediately following the fawning period (June–August). Bucks occurred most frequently on dry meadows during sexual segregation, and does and fawns primarily in moister meadows. Bucks occurred farther from summer sources of water than did other sex and age classes of deer. Sexual segregation was not attributable to food habits or selection of vegetative types. However, the percent cover of Sisymbrium altissimum, a preferred food, was higher and in earlier phenological stages on ranges occupied primarily by does than in meadows where bucks predominated. The proportion does and fawns comprised of all deer in eight meadow systems was correlated positively with overall population density; an inverse relationship existed between the proportion of bucks and deer density. Consequently, the availability of forage per individual did not vary between ranges inhabited by bucks and does. Sexual segregation in southern mule deer may occur as a result of the greater needs for water of lactating does. Larger body size and rumen to body volume ratio of bucks reduce rates of water loss and may allow males to subsist on vegetation in drier phenological states.