Efficacy and ecological effects of predator control in south Texas by Frederick Stewart Guthery

Abstract

The effects of mammalian predator control on (1) the productivity and survival of Angora goats and (2) population trends of game and nongame wild life were studied during January-July 1975 and 1976 in northern Zavala County, Texas. One hundred thirty-two coyotes (Canis latrans) and 18 bobcats (Lynx rufus) were killed on a 15.5-km?? treated (predator control) area. This lowered density of these predators by 60-85 percent when compared with an untreated (no predator control) area. Predators killed 33-95 percent (33-95 percent of losses) and 16-59 percent (22-81 percent of losses) of kids born on untreated and treated pastures, respectively. Although predator control increased the kid crop by 2,700 percent, the crop was only 13.5 percent under treatment. Predators killed 49 of 205 nannies (24 percent of flock, 91 percent of losses) in the untreated pasture. No nannies were killed by predators in the treated pasture but 10 percent of the flock succumbed to nonpredator mortality. Coyotes were responsible for most, if not all, predation losses. Coyotes selected the youngest, smallest kids. Nannies killed by coyotes were significantly (P < 0.01) smaller than nannies surviving. Cottontail (Sylvilagus floridanus) densities increased in both areas during 1975; the rate of increase was higher (P < 0.05) on the untreated area. Cottontail densities declined at similar rates (P > 0.05) in 1976; during both years density fluctuated independent of predator abundance. Predator control had little detectable influence on population trends of bobwhite (Colinus virginianus) and scaled (callipepla squamata) quail. Predator control had little apparent effect on rodent populations. The probability of an individual rodent surviving from one month to the next was similar (P>0.05) in both areas..