Waking and roosting of Grey-crowned Babblers Pomatostomus temporalis in South-east Queensland during Spring

Abstract

From August to December 1980 we studied the social roosting of two groups of communally breeding Grey-crowned Babblers Pomatostomus temporalis to try to discover why birds entered or left the roost at the observed times. Stepwise multiple regressions showed that time of sunrise (or sunset) was the most important predictor of departure (or roosting) time, as expected, followed by light intensity and then cloud cover. Temperature and relative humidity were statistically unimportant, except for one group (Group 51) at roosting, where humidity appeared to be a significant variable. However, humidity was directly correlated with cloud cover and may thus have been only indirectly related to roosting. Group 51 roosted significantly earlier than Group 56, but tended to leave the roost earlier as well. Therefore both groups were active for about the same length of time each day. Group 51 roosted earlier relative to sunset as the season progressed, whereas Group 56 showed no such tendency. The observed differences between groups cannot reflect dif- ferent ecological factors, because the groups occupied physically similar adjacent home ranges. Instead, they suggest a random effect of social behaviour on an otherwise straightforward set of responses.