Studies on the communal roosting of starlings (stumus vulgaris L.)

Abstract

This study set out to investigate the roosting behaviour of the Starling at rural roosts and in particular to examine the mechanisms of roosting. It was hoped that insights into the function and selective advantage of the social roosting habit would be gained through an under standing of the mechanics of roost entry and departure. Estimates of the size of major winter roosts were obtained regularly, liandom samples of birds were shot, from within one roost, in order to determine the age, sex and origin of the roosting population. Emphasis was placed on the measurement of the light regime together with the observation and timing of roost entry and dispersal. Multivariate analysis was used to investigate the variation of several aspects of roosting behaviour with respect to environmental factors. Small Starling roosts, occupied during the early autumn, amalgamated to form major roosts, which served large catchments, throughout the winter. At that time of year the resident population was swollen by the arrival of Continental birds. These Continentals constituted 50% of all birds shot at the one roost examined and the sample contained fewer males than did the sample of British birds. The pattern of roost entry varied according to light and weather conditions. The time of entry also varied, being later relative to civil twilight in the middle of the winter. Departure from the roost in the morning was earlier when day length was shorter. Moreover, departure waves were less numerous and of smaller total duration at that time of year. The various hypotheses on communal roost functions have been examined in the light of the information gained during this study. The mechanism of wave dispersal, from the communal roosts of Starlings, does offer the opportunity for roosts to act as "information centres" for food finding.