TWEL Gretchen Anchor Thesis

Impacts of Coyotes (Canis latrans) on White-tailed Deer (Odocoileus virginianus) Behavior and Mortality in the Chicago Region

Gretchen C. Anchor, MS

Advisor:  Stanley D. Gehrt

Thesis

White-tailed deer (Odocoileus virginianus) and coyotes (Canis latrans) have spread into metropolitan areas in recent decades.  How these species interact with the landscape, other species, and each other is of interest to managers of these human-dominated areas.  In the Chicago region, little is known about the relationship of white-tailed deer and coyotes.  Our study aimed to elucidate the predator-prey relationship as well as how white-tailed deer respond behaviorally to coyotes as a result of this relationship.  To answer questions on the predator-prey relationship between these two species, 81 white-tailed deer fawns were collared and monitored to determine causes of mortality.  The analysis of 172 coyote scats also provided insight into this relationship by determining dominant food sources.  Predation by coyotes was the primary cause of mortality (77.8%) of white-tailed deer fawns at our study site.  Furthermore, white-tailed deer remains were found in most coyote scats (53.5%) but the presence of these remains were highest in scats collected in the summer (83.9% in 2017; 61.3% in 2018).  The results of the fawn mortality analysis and scat analysis suggest that there are high incidents of coyote predation on white-tailed deer fawns but provide little evidence of predation on adults.  With this specific predator-prey relationship, there is potential for behavioral asymmetries between age classes and sexes of white-tailed deer.  To determine how this relationship influences white-tailed deer behavior, we chose to study antipredator behaviors because these behaviors are expressed in relation to predation risk. Following the “ecology of fear” framework, we expected to see increases in antipredator behavior by fawns and does with fawns in response to coyotes.  We predicted, however, that the overall white-tailed deer population at our study site would not show strong antipredator behavior towards coyotes due to the possibility of habituation as a result of exposure to high coyote densities.  We chose to investigate the antipredator behaviors of vigilance and avoidance in response to coyotes.  Through the use of camera traps, we captured white-tailed deer foraging behavior in response to an indicator of coyote presence, specifically coyote urine.  Through this test, we found that white-tailed deer of each age class and sex do not increase the amount of time spent vigilant while foraging when an indicator of coyote presence was present.  To look for signs of avoidance of coyotes, white-tailed deer and coyotes were fitted with radio collars and monitored concurrently.  Home range overlap was found for all deer-coyote dyads studied indicating that white-tailed deer are not selecting home ranges that allow the complete avoidance of coyotes.  After analysis using the half-weight association index, however, results suggested avoidance behavior occurred for all deer-coyote dyads.  These results show that the white-tailed deer monitored in our study avoid being within 200 m of coyotes.  The results of both the vigilance survey and avoidance testing provide evidence of habituation, regardless of age class and sex, to an indicator of coyote presence and the lack of avoidance at the landscape level.  These results, however, indicate that white-tailed deer at this site show finer-scale avoidance by avoiding coming into close proximity with coyotes.  Our study provides valuable information on the coyote-deer predator-prey relationship and the behavioral responses of deer to this relationship in the Chicago region.