Anti‐Predator Strategies and Grouping Patterns in White‐Tailed Deer and Mule Deer

Abstract

White‐tailed deer (Odocoileus virginianus) and mule deer (O. hemionus) are closely related species of similar size that differ in their anti‐predator behavior. White‐tails flee from coyotes (Canis latrans), whereas mule deer typically stand their ground and attack this predator. I used observations of coyotes hunting deer to identify: (i) changes in group structure made in response to coyotes; and (ii) the relationship between group structure and the risk of predation for each species. In response to coyotes, groups of mule deer merged with other groups and individuals bunched together. Predation attempts were more likely to escalate when groups split and individuals failed to bunch. Coyotes typically attacked mule deer that were in outlying positions, and these deer had to move to central positions to end attacks. Due to the high frequency of attacks on small groups as well as to the level of dilution of risk, individuals in small mule deer groups were at high risk of being attacked compared with those in larger groups. In contrast to mule deer, white‐tails made no consistent changes in group size or formation, and coyotes attacked individuals in central as well as in outlying positions. Variation in aspects of group cohesion was not related to the vulnerability of white‐tails, and there was no obvious difference in the risk of attack facing individuals in groups of different size. These results suggest that coyote predation selects for relatively large, cohesive groups in mule deer, apparently because this type of group improves their ability to deter coyotes. Coyote predation does not have similar effects on groups formed by white‐tails, which use flight rather than deterrence to avoid predation. The benefits of responding cohesively, occupying certain positions within groups, and forming groups of a certain size can vary widely depending on the anti‐predator strategies used by an animal.

Fight or flight? Antipredator behavior and the escalation of coyote encounters with deer

“…The most common form of aggression was observed when coyotes encountered or pursued a group. Depending on the size of the group, one to a few females would walk or trot toward the coyotes, assuming a threat posture, to keep the coyotes away from the group, which was typically bunched together at the time (Lingle 2001). When interactions escalated and coyotes attempted to lunge at or run after a deer, females stotted after the coyotes, striking them with their fore limbs.…”

“…Deer showed similar behaviors regardless of where they lived even though they were encountering different coyote packs. Furthermore, speciestypical responses were seen when coyotes encountered or attacked mixed-species groups (Lingle 2001).…”

“…There are other components to the mule deer's response that appear to increase their ability to deter coyotes. Mule deer tend to move to rugged terrain or high points and to bunch closely together with companions before reorienting to coyotes (Lingle 2001(Lingle , 2002. As long as they stand close together, coyotes are unlikely to single out an individual for attack.…”

“…Flight, however, appeared useful as a temporary tactic that enabled deer to improve their position in some way. If a mule deer stood in place, but was alone, coyotes were likely to attack it (Lingle 2001). Individuals would therefore move to join a group and groups moved to join another group or to get to rugged terrain, and then stopped after reaching these locations.…”

“…In the wild, white-tails have been reported to flee when attacked by wolves and they do so by galloping (Mech 1970). In response to coyotes, mule deer frequently stay in place, at times attacking the predator (Bowyer 1987), and they also bunch together for protection (Lingle 2001). When they do flee, mule deer are more likely to stot than to gallop and, regardless of their gait, they are considerably slower than white-tails (Eslinger 1976;Lingle 1992).…”