PRONGHORN RESPONSE TO COYOTE CONTROL- A BENEFIT: COST ANALYSIS'

Abstract

The population of pronghorns (Antilocapra americana) on Anderson Mesa in north-central Arizona has exhibited a strong correlation between coyote (Canis latrans) suppression and pronghorn fawn survival over the last 40 years (Arrington and Edwards 1951, Neff and Woolsey 1979). Similar relations have been reported with pronghorns in Utah (Udy 1953) and Texas (Hailey 1979) and with white-tailed deer (Odocoileus virginianus) in Texas (Guthery and Beasom 1977) and Oklahoma (Stout 1982). The Anderson Mesa herd gradually declined after about 1955, and was reduced 85% by a blizzard in 1967 (White 1969). By 1970 the 115 survivors had increased to 350. Intensive annual coyote control by toxicants was then terminated. The herd peaked at 481 in 1971 and increased no further. Age ratios dropped from 90 fawns/100 does in 1975 to a low of 14 in 1979. Beginning in 1979 experiments were conducted to determine if coyote densities could be reduced sufficiently to affect fawn survival rates and allow the population to increase (Neff et al. 1985). The coyote population was effectively reduced over a 3-year period (1981-1983) by helicopter gunning after trapping and shooting had proved inadequate. This control effort, conducted just prior to fawning, has been coincidental with more than a 400% increase in the pronghorn population of the study area from 1980 to 1983. This paper describes a computer simulation