Correlates Of Group Living In Southern Mule Deer (odocoileus, Population Characteristics, California, Distribution, Predation).

Factors related to group formation in a nonmigratory population of approximately 250 southern mule deer (Odocoileus hemionus fuliginatus) were studied on East Mesa, Cuyamaca Rancho State Park, San Diego County, California from June 1977 - January 1979. The mean size of 2,639 groups of deer was 3.5 (SD = 2.1). The distribution of deer was influenced greatly by the availability of vegetative types, preferred foods, and sources of free water during summer. Variation in the size and quality of these important and often clumped resources, however, failed to produce expected changes in deer group size. Thus, resources may help limit group size by regulating the number of individuals available to form groups, but are not a direct cause of group living in deer. Deer group size was related directly to monthly precipitation and varied inversely with monthly temperature. Changes in group size, however, might be brought about by the influence of these climatic variables on vegetation, and thereby indirectly affect group formation in deer. The group size of deer was correlated with a number of variables that were related to the likelihood of encountering or deterring predators. Deer group size declined with increased concealment cover provided by vegetative types, and grew as deer moved further from escape cover. The percent of deer feeding increased with group size, whereas alert-alarm behavior declined. Coyotes (Canis latrans) behaved less aggressively toward larger groups of deer. Rates of aggressive interactions for individual deer declined with increasing group size; individuals spaced themselves further apart as groups became larger. Groups of southern mule deer appear to be limited in size by resources and topography, but not by social interactions. Data overwhelmingly indicate that predators are responsible for group formation in deer, although sufficient resources must be present to allow for group living.Ph.D.Biological SciencesEcologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/127695/2/8512369.pd