Demographic and Spatial Responses of Coyotes to Changes in Food and Exploitation

Lethal control for reducing carnivore populations is a contentious issue throughout the world. While computer simulations have been developed modeling the effects of population reduction on coyote (Canis latrans) population parameters, testing these hypotheses with empirical data from the field is lacking. We documented the demographic and spatial responses of coyotes to changes in the levels of food resources and human exploitation on the Piñon Canyon Maneuver Site, southeastern Colorado. We captured, radio-collared, and tracked 92 (53 M: 39 F) coyotes from March 1983 to April 1989. Of these, 74 animals were residents from 32 packs, plus 12 transients; 6 animals were captured while making dispersal movements. We collected 14,147 telemetry locations of the radioed coyotes spanning 7 years of study. We compared coyote pack size and density, survival rates, reproduction (litter size, litter sex ratio, % yearlings reproducing), and home range size between years receiving exploitation (1987-88) versus years receiving no exploitation (1983-86) and post-removal (1989), as well as, comparisons of these parameters between removal and non-removal areas within years. Changes in estimates of pack size and coyote density, plus the number of animals removed, indicated the coyote population was reduced 44-61% and 51-75% in the removal area during 1987 and 1988, respectively. As expected, annual survival rates declined significantly for coyotes in the removal area compared to coyotes in the non-removal area. Removals brought about a drastic reduction in pack size and a corresponding decrease in density. However, both pack size and density rebounded to pre-removal levels within 8 months post-removal. Home range size did not change in response to changes in exploitation. Coyotes in the removal area appeared to maintain their normal (i.e., pre-removal) home ranges after coyotes were removed from neighboring territories. Following removals, the population shifted to a younger age structure (i.e., more yearlings). Litter size significantly increased in the removal area 2 years after the beginning of exploitation. However, changes in litter size were confounded by changes in the prey base. Litter size was significantly related to rabbit abundance, while rodent abundance was less of a factor influencing reproductive effort. Accounting for both changes in prey abundance and coyote density, litter size was significantly related to total prey abundance/coyote. With increasing prey and reduced coyote density, mean litter size doubled in the removal area compared to pre-removal levels; females in the non-removal area also increased litter size in response to increased rabbit abundance. Litter sex ratio favored males during years of no exploitation, changing to a preponderance of females during the 2 years of exploitation. Reproduction by yearlings increased from 0% in years prior to exploitation, to 20% following 2 years of coyote removal