Stay calm and keep grooming: exploring the link between vigilance and self-grooming in wild fallow deer under wolf predation risk

Predation is a key ecological interaction shaping prey populations through both consumptive and non-consumptive pathways, influencing prey behavior and eliciting antipredator responses. Vigilance is a fundamental antipredator strategy that may induce stress and motivational conflict in prey, potentially giving rise to displacement activities. Among these activities, self-grooming is a behavior widely recognised as an anxiety and stress-ameliorating response across many taxa. However, its role in wild ungulates remains poorly understood. We investigated the relationship between self-grooming, vigilance, and perceived predation risk in a wild, gregarious ungulate, the fallow deer, in an area recently recolonised by wolves. Using an extensive camera-trapping dataset, we quantified the relationship between vigilance and three indices of self-grooming (probability, frequency, and proportion), while testing the effects of age, sex, season, wolf and human visitation rates, habitat openness, and group size. Our results revealed a strong, direct relationship between vigilance rate and all three self-grooming indices. In contrast, group size, wolf detection rate, and season showed weak or inconsistent effects. Habitat openness was associated with reduced self‑grooming in some models for males, although only one of these models was weakly significant. Age and sex also weakly influenced self-grooming patterns: younger males groomed less frequently, while younger females groomed more frequently than adults. Overall, our findings provide the first evidence that self-grooming in fallow deer is closely linked to vigilance, supporting its interpretation as a vigilance-linked self-directed behavior. These results highlight the potential of self-grooming as a non-invasive behavioral indicator of perceived risk in wild ungulates, with important implications in predator-recolonised landscapes.