External body temperature and vigilance to a lesser extent track variation in predation risk in domestic fowls

Abstract Background The animal ecology literature proposes the view that predation risk induces fear in prey animals, but it is also possible that behavioral and physiological changes induced by predation risk are not associated with fear at all. If we view fear as a state indicated by measurable changes in behavior and physiology caused by threats, then it is valid to search for a link between markers of fearfulness and predation risk. I predicted that domestic fowls (Gallus gallus domesticus) foraging alone, and thus exposed to higher predation risk, would show higher vigilance (a behavioral marker of fearfulness) and lower external body temperature (a physiological marker of fearfulness) than domestic fowls foraging in pairs. These adjustments should become less prominent in the continued absence of threats during a trial. Results Domestic fowls that foraged alone rather than in pairs showed higher vigilance and lower external body temperature. While external body temperature returned to baseline values during a trial, vigilance unexpectedly increased. The results thus provide mixed support for an association between markers of fearfulness and predation risk. Conclusions I argue that vigilance is not always a sensitive marker of fearfulness because hunger can keep vigilance low even in risky settings. By contrast, external body temperature varied with group size and time during a trial, suggesting that this marker is more sensitive. Future studies are needed to validate the relationship between markers of fearfulness and predation risk.