Temporal structuring of vigilance behaviour by female Thomson's gazelles with hidden fawns

Prey animals often face a trade-off between investing time in antipredator behaviour and performing self-maintenance activities, such as foraging. Parents face particularly high stakes as they must protect highly vulnerable offspring while also meeting elevated energetic demands. To optimize this trade-off, the risk allocation hypothesis predicts that prey should adjust their antipredator behaviour to reflect temporal fluctuations in risk. That is, they should invest more in antipredator behaviour when risk is high and prioritize other activities when risk is low. Here we investigate whether changes in risk level resulting from periodic fawn exposure drive maternal vigilance patterns in Thomson's gazelle, Eudorcas thomsonii. We find that maternal vigilance patterns match the predictions of the risk allocation hypothesis. Mothers are highly vigilant prior to fawn retrieval, when risk of fawn detection by predators is high. They exhibit low levels of vigilance after fawns resume hiding, when certainty of predator absence is high and, therefore, risk is low. We suggest that fawn active periods may function secondarily as a form of predator sampling and that mothers may adjust their vigilance levels in response to information yielded by this sampling.