ROLE OF BODY-SIZE IN THE DIETS OF SYMPATRIC GRAY AND CULPEO FOXES

Feeding ecology of sympatric South American gray fox (Dusicyon griseus ) and culpeo fox (D. culpaeus) was studied from 1987 to 1990 in Torres del Paine National Park, Chile, to determine if these canids have dif ferent patterns of prey selection. Seasonal and species differences in use of prey were compared with availability of prey to determine prey selection by these foxes. Mammals accounted for 90% of 851 items of v ertebrate prey occuring in 890 feces of gray foxes. The European hare (Lepus capensis) was the most common vertebrate prey (45%), with lesse r amounts of the guanaco (Lama guanicoe; 14%) and Akodon (13%). Of 784 items of vertebrate prey in 645 feces of culpeo foxes, 93% were mamma lian. The European hare accounted for 69% of the prey items, and roden ts 20%. The proportion of vertebrate prey items consumed by gray and c ulpeo foxes changed seasonally. Yearly diets of gray and culpeo foxes were significantly different, with ungulates and the European hare con tributing most to the difference. Gray foxes were more omnivorous than culpeo foxes, feeding more on beetles and plants, especially from spr ing through autumn. Gray foxes had a significantly higher (XBAR +/- SE ) index of food-niche breadth for vertebrates than did culpeo foxes (0 .24 +/- 0.01 versus 0.09 +/- 0.01) and consumed vertebrate prey of a s ignificantly lower mass (2.17 +/- 0.07 versus 2.59 +/- 0.09 kg). The i ndex of similarity between the diets of the two species was low (0.14) . Differences in feeding habits between gray and culpeo foxes evidentl y are attributable to differences in food availability in their respec tive habitats.