Red Fox Prey Demands and Implications to Prairie Duck Production

Abstract

Experiments were conducted during spring and summer with 33 red foxes (Vulpes vulpes) to determine prey demands, feeding characteristics, and growth rates using natural foods. Pups began eating prey the 4th week after birth. Then, prey consumption averaged 1.38 and 1.90 kg/pup/week for weeks 58 and 9-12 of the denning season respectively, and 2.54 kg/pup/week for the postdenning period. Feeding by adults averaged 2.25 kg/adult/week. Free water was not needed by either pups or adults. About 90 percent of the prey offered to pups on simulated natural diets was consumed; remains varied with prey availability and prey type. Prey biomass required by a typical fox family was estimated at 18.5 kg/km2 for the 12-week denning season and 2.4 kg/km2/week for the postdenning period. Because of the large prey demands, ducks could represent a small part of the foxes' diet and yet be of consequence to the productivity of particular species. An example is provided for the mallard (Anas platyrhynchos). J. WILDL. MANAGE. 42(3):520-527 Many studies (e.g., Errington 1935, Scott 1943) show that red foxes are largely carnivorous, but few studies document the quantities of natural prey required. Knowledge of prey requirements is useful for assessing fox impact on prey populations. During summer and winter individual red foxes eat 0.38-0.57 kg of prey per day (Scott 1943, Lockie 1959, Vogtsberger 1972, Ryszkowski et al. 1973). Red foxes have high prey assimilation rates with 85-97 percent being digestible depending on food type (Vogtsberger and Barrett 1973, Litvaitis and Mautz 1976); 87 percent of the ingested energy is used for body maintenance (Vogtsberger and Barrett 1973). Red foxes are not noted for gorging or for carrying heavy fat loads; thus, survival seems to depend on regular feeding. Behavioral traits such as caching (Murie 1936, Macdonald 1976) insure the availability of food during periods of prey scarcity. The purpose of this paper is to provide quantitative estimates of prey demands (including nonconsumed prey parts) of adult and pup red foxes during the spring and summer pup-rearing period, and to relate these demands to predation on prairie nesting ducks during the nesting period. Emphasis is on the approximate 12-week red fox denning season which in the northern prairie region begins in early April and coincides with the duck nesting season (Sargeant 1972). This period is of particular consequence because adult foxes are caring for pups and because predation then can affect duck production in local areas. I appreciate the assistance of S. H. Allen and R. T. Eberhardt in capturing the foxes, of numerous individuals from the Northern Prairie Wildlife Research Center and the North Dakota Game and Fish Department in providing prey, of L. E. Eberhardt and T. J. Dwyer in conducting feeding tests, and of G. L. Pearson for diagnostic services. D. H. Johnson provided statistical advice and together with G. L. Krapu and R. J. Greenwood critically reviewed the manuscript; drafting was by C. W. Shaiffer. G. L. Krapu and C. W. Dane provided unpublished data on duck weights in spring.