Using sterilization to change predation rates of wild coyotes: A test case involving pronghorn fawns

Abstract

Surgical sterilization of coyotes (Canis latrans) reduced their predation rate on domestic sheep. We investigated whether sterilizing coyotes would similarly change coyote predation rates on pronghorn antelope (Antilocapra americana) neonates. From May 2006 to March 2008, we radio-collared 71 pronghorn fawns to determine survival rates in southeast Colorado, USA. During the first year of the study, all coyotes were reproductively intact. During the second year, we surgically sterilized 15 coyotes from 10 packs in the southern half of the study area, while nine coyotes from seven packs in the northern half were given sham sterilizations (i.e., remained reproductively intact). In addition, we estimated the availability of alternative prey and coyote density on both areas to evaluate predator-prey factors that could interact with the sterilization treatment. Using the known fate model in Program Mark, we constructed models with and without a treatment effect, plus year, area, individual covariates, alternative prey indices, and predator density to estimate pronghorn fawn survival rates. Results from model averaged parameter estimates and cumulative summer survival indicated coyote sterilization increased survival rates of pronghorn fawns by reducing predation rates of fawns. While fawn survival was higher overall in the north area, after treatment was applied, cumulative pronghorn fawn survival during the summer of 2007 in the south area was 242% higher for pronghorn fawns captured in sterile coyote territories (0.44; 79-day interval survival rate) compared to fawns captured in intact coyote territories (0.18). There was also a significant local area effect, but no relationship between fawn survival and individual fawn covariates of sex, birth weight, birth date, or age. No relationship was detected between fawn survival and lagomorph abundance index, rodent abundance index, or coyote density. Surgical sterilization of coyotes was useful in reducing predation rates on pronghorn fawns.

Factors Influencing Survival Rates of Pronghorn Fawns in Idaho

“…Predators may be satiated with alternate prey during periods when prey are abundant, thereby buffering the need for coyotes to prey on fawns during a neonate's vulnerable time (Hamlin et al 1984, Berger et al 2008). Our study supported this premise, whereas a previous study found rabbit abundance did not influence fawn survival in southeastern Colorado (Seidler et al 2014). Lagomorphs have population cycles throughout the Intermountain West (Clark 1972, Wagner 1981, Stoddart et al 2001) and how these cycles influence fawn survival is presently unknown.…”

“…In general, ungulate populations have low fawn survival (Fowler 1987, Gaillard et al 1998) and neonates are the most susceptible age class for morality (Caughley 1966, Fowler 1987, Linnell et al 1995). Population dynamics of pronghorn populations are variable, but survival rates of pronghorn neonates are generally low (Gregg et al 2001, Dunbar and Giordano 2003, Seidler et al 2014). Survival of neonatal pronghorn are affected by a variety of factors including nutrition, predation, disease, and weather (Beale and Smith 1973, Byers 1997).…”

Home range size, vegetation density, and season influences prey use by coyotes (Canis latrans)

“…Territoriality is a behavioral tactic for partitioning space and defending food sources [ 65 – 67 ] that plays a fundamental role in coyote ecology and is rarely accounted for in diet studies (but see [ 4 , 16 , 68 , 69 ]). Space use by resident coyotes is constrained by their territorial behavior, as they rarely venture outside their home ranges unless they are dispersing offspring [ 20 , 36 , 70 ].…”

Using the “placeholder” concept to reduce genetic introgression of an endangered carnivore

“…Sterilization has been used in the recent past to reduce predation rates by coyotes on domestic and native ungulates (Bromley and Gese, 2001a;Seidler et al, 2014), but using sterilization to limit genetic introgression into the red wolf population is the first use of sterile animals within the context of the "placeholder" concept. We emphasize that sterilization was not used to limit the distribution or size of the coyote population, but to reduce the incidence of hybridization between coyotes and red wolves and genetic introgression into the red wolf population.…”

“…As part of the RWAMP (Kelly, 2000), sterilization of coyotes and hybrid animals was proposed to reduce genetic introgression into the red wolf population. While sterilization has been tested as a management tool to reduce predation on domestic livestock and wild neonatal ungulates (Bromley and Gese, 2001a;Seidler et al, 2014) and proposed as a method for population control (Mech et al, 1996;Haight and Mech, 1997), using sterilization to reduce genetic introgression was a novel application. In essence, sterilized coyotes and hybrids would be allowed to remain on the landscape, maintaining social bonds and territories (Bromley and Gese, 2001b;Seidler and Gese, 2012), and serve as "placeholders" that would maintain territories, thereby reducing residency of home ranges in the recovery area by reproductive coyotes or hybrids, and thus reducing the threat of hybridization with a red wolf (i.e., producing hybrid offspring if pairing with a red wolf occurred; Stoskopf, 2012) and facilitating expansion of the red wolf population.…”