Weather conditions affect the collective roosting behaviour of the Cattle Egret Bubulcus ibis

Capsule: Collective roosting behaviour of the Cattle Egret Bubulcus ibis was influenced by the weather and the season. Aims: To document the roosting behaviour of the Cattle Egret and assess the relationship between weather conditions and four components of the roosting behaviour including the population size, duration of roost occupancy, the timing of roost gathering and the rate of arrival at roost. Methods: We recorded the number and arrival times of individuals occupying a communal roost site in northeast Algeria in 2013-2014 between December and April. Results: There was a seasonal decline of the flock size and rate of arrival and a seasonal increase in the duration of gathering. Weather conditions affected all variables assessed in roosting behaviour such that bad weather lowered the number of individuals in the roost, lengthened the duration and advanced the timing of gathering, and reduced the rate of gathering in the roost. Conclusion: Our study highlights the importance of weather conditions in shaping the collective roosting behaviour of a gregarious species. Our results suggest that future changes in climatic conditions might influence the collective behaviour of the Cattle Egret in particular and gregarious birds in general.