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

Provisioning rates to nestlings by adult birds may be influenced by many fa ctors. In cooperatively breeding species, an increase in the number of help ers at the nest may increase total provisioning rate, but in some cases cer tain individuals will reduce their provisioning effort so that overall prov isioning rate does not change with the number of provisioners. I examined n umerous environmental and demographic factors that may correlate with provi sioning rate in the cooperatively breeding Rufous Treecreeper, Climacteris rufa, in the south-west of Western Australia. A total of 102 nest watches o f colour-banded birds was conducted over 3 years. Provisioning rate per hou r varied from 8 to 50 (mean +/- s.e = 21.8 +/- 0.91). There were significan t positive relationships between provisioning rate and number of nestlings and nest stage, and negative associations with time of day and maximum dayt ime temperature. Provisioning rate was highest when there were two nestling s and nestlings were near fledging, early in the morning (before 09:00 hour s) and during mild temperatures (20-30 degreesC). There was no relationship between provisioning rate and the number of helpers at the nest because th e primary (assumed to be breeding) male and female reduced their provisioni ng effort as the number of helpers increased.