The Trials of Motherhood: Maternal Behavior Patterns and Antipredator Tactics in Thomson's Gazelle, a Hiding Ungulate

Abstract

This dissertation examines risk management tactics of female Thomson's gazelles during the early stages of motherhood, when fawns experience high predation risk. Fawns' main defense is the hiding strategy, in which they spend long periods of time concealed in vegetation apart from their mothers. Hiding requires maternal cooperation and has the potential to affect maternal risk and behavioral patterns.

Immediately following birth, the fawn is unable to hide. Avoidance of fawn predation depends on the social and environmental contexts of parturition. Most mothers either isolate from conspecifics and give birth in tall grass or remain in social groups and give birth in short grass. The latter tactic provides greater protection from conventional predators, but pressures such as conspecific harassment may lead mothers to give birth in isolation. Both tactics improve neonates' survival probability compared to behavior that is inconsistent with either tactic.

Once hiding begins, fawns are concealed and relatively safe from detection by predators, and mother-fawn interactions are limited to brief active periods. This framework affords mothers the freedom to schedule investment behaviors and minimize the impact of motherhood on their activity. Peaks in maternal vigilance precede and coincide with active periods, when fawns are at greatest risk. Outside of active periods, mothers are able to behave identically to non-mothers.

As fawns transition out of the hiding strategy, they increase their exposure to predators. More frequent activity periods enable fawns to move hiding spots more often, which allows mothers to track group movements more effectively. Mothers and fawns rely on increased time spent in social groups and in short grass habitats to mitigate the increase in fawn risk. Thus, as fawns transition out of hiding, mothers transition back to normal activity, grouping, and habitat use patterns.

During predator attacks, mothers must respond to actual rather than potential risk. In an experiment involving simulated predator attacks, we found that mothers do not rely on group vigilance to detect potential fawn predators, that they exhibit riskier responses than non-mothers, and that the presence of a mother in a group can affect the group's response in ways that may reduce maternal risk.