Variability in provisioning rates to nestlings in the cooperatively breeding Rufous Treecreeper, Climacteris rufa

Abstract

Provisioning rates to nestlings by adult birds may be influenced by many factors. In cooperatively breeding species, an increase in the number of helpers at the nest may increase total provisioning rate, but in some cases certain individuals will reduce their provisioning effort so that overall provisioning rate does not change with the number of provisioners. I examined numerous environmental and demographic factors that may correlate with provisioning rate in the cooperatively breeding Rufous Treecreeper, Climacteris rufa, in the south-west of Western Australia. A total of 102 nest watches of colour-banded birds was conducted over 3 years. Provisioning rate per hour varied from 8 to 50 (mean ± s.e = 21.8 ± 0.91). There were significant positive relationships between provisioning rate and number of nestlings and nest stage, and negative associations with time of day and maximum daytime temperature. Provisioning rate was highest when there were two nestlings and nestlings were near fledging, early in the morning (before 09:00 hours) and during mild temperatures (20–30°C). There was no relationship between provisioning rate and the number of helpers at the nest because the primary (assumed to be breeding) male and female reduced their provisioning effort as the number of helpers increased.