The effect of age on vigilance: a longitudinal study with a precocial species

Vigilance allows prey species to detect predators before it is too late to escape. While the adaptive value of vigilance has become clearer over the years, developmental questions have attracted little attention. I explored the effect of age and group size on vigilance in a precocial species, the domestic fowl (Gallus gallus domesticus). I recorded vigilance in groups of various sizes in juveniles and one year later in adults. Vigilance decreased with group size in juveniles and to a lesser extent in adults. Juveniles tested alone showed longer feeding and vigilance bouts than adults reflecting their inexperience with predation threats and more rapid satiation, respectively. Adults in larger groups were more vigilant reflecting the need to monitor aggressive conspecifics in addition to predators. Gradual acquisition of information about risk posed by predators and conspecifics and feeding constraints influenced the expression of vigilance as a function of age in this species.