Fear of the dark: night-time roosting and anti-predation behaviour in the grey partridge (Perdix perdix L.)

Abstract

[Numerous studies describing habitat preferences and anti-predation behaviour in the grey partridge (Perdix perdix) focus on the daytime. This is the first study analysing nighttime behaviour by means of thermography. In total 640 partridges, clearly avoiding field boundaries as roosting sites to roost in the open field, were observed. Comparing day- and night-time behaviour of partridges they not only perceive a 'predation risk landscape' but moreover a 'predation risk schedule' resulting in a circadian shift in anti-predation strategies. Furthermore, partridges were ascertained to roost in tighter groupings on darker nights. I hypothesize that the efficiency of visual detection decreases with deteriorating light conditions — confirmed by a decreasing flight initiation distance — and partridges huddle closer together fearing such an insecure situation. The preference to roost in smaller subunits within one covey is explained by a more efficient predator detection compared to tight groupings. In contrast to the day-time behaviour, at night the first choice as an escape movement is flying. Altogether partridge behaviour in winter at night was found to be well adapted to predator avoidance and energy economy, explaining the lower predation rates during the 'covey season' compared to the spring phases of dispersal, laying and incubation., Numerous studies describing habitat preferences and anti-predation behaviour in the grey partridge (Perdix perdix) focus on the daytime. This is the first study analysing nighttime behaviour by means of thermography. In total 640 partridges, clearly avoiding field boundaries as roosting sites to roost in the open field, were observed. Comparing day- and night-time behaviour of partridges they not only perceive a 'predation risk landscape' but moreover a 'predation risk schedule' resulting in a circadian shift in anti-predation strategies. Furthermore, partridges were ascertained to roost in tighter groupings on darker nights. I hypothesize that the efficiency of visual detection decreases with deteriorating light conditions — confirmed by a decreasing flight initiation distance — and partridges huddle closer together fearing such an insecure situation. The preference to roost in smaller subunits within one covey is explained by a more efficient predator detection compared to tight groupings. In contrast to the day-time behaviour, at night the first choice as an escape movement is flying. Altogether partridge behaviour in winter at night was found to be well adapted to predator avoidance and energy economy, explaining the lower predation rates during the 'covey season' compared to the spring phases of dispersal, laying and incubation.]