NWRC scientists use a multidisciplinary approach to 

 study interactions among predators and the impact 

 of predators and predator removal on ecosystems 

 and wildlife population dynamics. Results from 

 these studies are fundamental to selective predator 

 management, as well as to providing necessary 

 information in the NEPA process. 



Interactions Among Wolves, Coyotes, and 

 Pronghorn Antelope: Does Wolf Recovery Help 

 Pronghorns? — High coyote predation rates on 

 pronghorn fawns are common throughout the 

 Western United States. Scientists at the NWRC 

 Logan, UT, field station used a natural experiment 

 created by wolf recolonization in the southern 

 Greater Yellowstone Ecosystem to evaluate whether 

 wolf recovery would decrease the abundance of 

 coyotes and subsequently increase pronghorn fawn 

 survival due to reduced coyote predation. 



Results from a 3-year study involving spatial 

 contrasts of wolf densities, coyote densities, and 

 pronghorn fawn survival at control (wolf-free) and 

 experimental (wolf-abundant) sites provided strong 

 evidence of wolves' decreasing coyote numbers 

 and increasing fawn survival. The scientists 

 documented a more than fivefold increase in 

 pronghorn fawn survival at sites used by wolves 



Wolf recovery may be beneficial to pronghorn. Scientists have 

 noticed that, as coyotes interact with wolves in the northern 

 Rockies, coyote predation on pronghorn fawns declines. 



during summer and a nearly sixfold increase in fawn 

 survival at sites used by wolves year 'round. Results 

 indicated a negative relationship between coyote 

 and wolf densities, suggesting that interspecific 

 competition facilitated the increase in observed 

 fawn survival. Whereas densities of resident coyotes 

 were similar between control and experimental sites, 

 the abundance of transient coyotes was markedly 

 lower in areas used by wolves. Thus, differential 

 effects of wolves on solitary coyotes may be an 

 important mechanism by which wolves limit coyote 

 populations. 



These results suggest that widespread extirpation 

 of wolves may contribute to high rates of coyote 

 predation on pronghorn fawns. The results also 

 support a growing body of evidence demonstrating 

 the importance of top carnivores' influencing 

 smaller predators and their prey in structuring the 

 dynamics of terrestrial systems. 



Effects of Coyote Population Reduction on Swift- 

 Fox Demographics in Southeastern Colorado — The 



distribution and abundance of swift foxes have 

 declined from historic levels. Causes for the decline 

 include habitat loss and fragmentation, incidental 

 poisoning, changing land-use practices, trapping, 

 and predation by other carnivores. Coyotes overlap 

 the geographic distribution of swift foxes, compete 

 for similar resources, and are a significant source 

 of mortality for swift-fox populations. Current swift- 

 fox conservation and management plans to bolster 

 declining or recovering fox populations may include 

 coyote population reduction to decrease predation. 

 However, the role of coyote predation in swift-fox 

 population dynamics is not well understood. 



To better understand the interactions of swift 

 foxes and coyotes, scientists at the NWRC Logan, 

 UT, field station compared swift-fox population 

 demographics (survival rates, dispersal rates, 

 reproduction, density) between areas with and 

 without coyote population reduction. On the Pinon 

 Canyon Maneuver Site in Colorado, NWRC scientists 

 monitored 141 swift foxes for 65,226 radio-days 

 from 1998 to 2000 with 18,035 total telemetry 

 locations collected. In areas where coyotes 

 were removed, the juvenile swift-fox survival rate 



16 Developing Methods 



