Anthelmintic treatment affects behavioural time allocation in a free-ranging ungulate

Social, ecological and environmental factors all influence how much time animals allocate to different behaviours. Here, we investigated whether parasites affect behavioural time allocation in a free-ranging ungulate that must apportion time to multiple competing activities crucial for maintenance, survival and reproduction. We examined how experimental removal of gastrointestinal and pulmonary nematodes influenced the relative amounts of time that female Grant's gazelle, Nanger granti, allocated to core behaviours including foraging, vigilance, moving and resting. The anthelmintic treatment reduced female parasite load for ∼120 days, and during this period, females relieved of their parasitic nematodes adjusted their daily time budgets. At the group level, parasite removal resulted in an increase in foraging time and a decrease in vigilance. This effect was also apparent at the individual level, where treated females allocated more time to foraging at the expense of vigilance. In addition to treatment, group size was a significant predictor of the relative time spent foraging versus vigilant, where females in larger groups allocated more time to foraging at the expense of vigilance. Our results suggest that parasites may induce changes in host behaviour that are of similar magnitude to some of the most commonly studied social drivers of behavioural time allocation.