Ticks or lions: trading between allogrooming and vigilance in maternal care

- Behavioural adjustments to predation risk may incur costs to prey species.
- Food-related parameters interfere in the historical vigilance-foraging conflict.
- We focused on the antipredator-antiparasite trade-off during maternal care.
- The higher the alertness level, the lower the maternal allogrooming probability.
- Group size, habitat characteristics and calf sex are related to alertness level.

Behavioural adjustments to predation risk may impose costs on prey species. While the vigilance-foraging conflict has been extensively investigated, other important fitness-related behaviours exclusive to scanning, such as grooming, have been overlooked. Yet, risk perception is expected to be more accurately assessed in these contexts as food-related parameters should not interfere. We studied individually recognizable impalas, Aepyceros melampus, and questioned the factors that shape maternal decision making in two exclusive components of maternal care with high benefits and costs: scanning for predators and grooming offspring to remove parasites. While studies generally infer prey alertness level, used as a proxy of risk perception, from the observed investment in vigilance, the vigilance-allogrooming context gave us the opportunity to directly assess alertness during the time spent head-up, and then to investigate its sources of variation and its consequences for allogrooming probability. We found a strong decrease in allogrooming probability when maternal alertness increased. Mothers were more alert in open (grassland) than in closed (bushland) habitats at a large scale. Increasing group size led both to lower maternal alertness and higher proportion of suckling time spent allogrooming, but only when surrounded by low vegetation, the reverse being true in high vegetation. Finally, mothers suckling female calves were more alert. Our results underline the determinant role of habitat, shaping both offspring predation risk and the relative conspicuousness or protective value of group mates. We discuss the potential fitness costs associated with the antipredator-antiparasite trade-off faced during maternal care. Our results suggest that prey behaviours other than foraging are essential to identify factors shaping risk perception.