Dietary Overlap among Axis, Fallow, and Black-Tailed Deer and Cattle

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Seasonal diets of native Columbian black-tailed deer (Odkoileus hemionus cohunbbznus) and exotic axis deer (Axis axis axis), fallow deer (Dama dama dama), and cattle (Bos taurus) on Point Reyes National Seashore were determined by microhistological technique to assess their dietary overlap. Throughout the year black-tailed deer ate mostly forbs, axis deer and fallow deer ate mostly grasses and forbs, and cattle ate mostly grasses. Only a few plant species comprised most of their diets. Percent composition of food species was not related to their preference indexes. Diets of axis and fallow deer overlapped more with each other and cattle than with black-tailed deer except during the summer when the dietary overlap among all species was similar at a lower level. Comparison of seasonal diets of deer with this and other studies indicated that food consumption of deer was not limited to particular food classes. Authors are former graduate student, Department of Agronomy and Range Science, University of California, Davis and now consulting biologist, 1012 Sand Bar Circle, Carmichael, Calif. 95608; and associate professor, Department of Forestry and Resource Management, University of California, Berkeley. The project was funded by the National Park Service-Western Region. Carole F. Truman and Jennie Dushek determined composition of food species. Drs. William M. Longhurst and John W. Menke were advisors to this project. Manuscript accepted January 28, 1985. 546 Exotic ungulates introduced into favorable habitats may erupt in numbers, deplete their food resources, and then crash (Scheffer 1951, Klein 1968, Caughley 1970). At Point Reyes National Seashore, as a result of an introduction of 2 species of exotic deer during the 1940’s and early 1950’s (Wehausen and Elliott 1982) and the continuation of commercial beef and dairy operations, 4 ungulates now coexist in the Seashore’s pastoral zone: cattle (Bos tauno); Indian axis deer (Axis axis axis), European fallow deer (Dama dama dama); and native Columbian black-tailed deer (Odocoileus hemionus columbianus). Previous studies at Point Reyes National Seashore (Elliott 1973, Wehausen 1973) suggested that these deer and cattle have similar diets, and that unlimited growth of the exotic deer population could have significant negative effects on the nutrition of all resident ungulates, particularly in the fall when the amount of the forage and its nutritional value are low. Since the National Park Service was shooting the exotic deer within the pastoral zone to maintain their density at 1973 levels and knowledge of the ecological relationships between these species and their habitat was limited, this project was undertaken to provide information on which to base management decisions. JOURNAL OF RANGE MANAGEMENT 36(6), November 1965 Many studies have indicated that competitive effects between sympatric ungulate species involved the use of food (Anthony and Smith 1977, Sinclair 1977, Mackie 1978, McCullough 1980, Kasworm et al. 1984). Therefore, to investigate the likelihood of competition among deer and between deer and cattle at their current densities on Point Reyes Peninsula, the botanical composition of their diets, their preference for these food species, and their dietary overlaps were assessed.