Does Group Size Affect Field Metabolic Rate of Arabian Babbler (Turdoides squamiceps) Nestlings?

Abstract

Abstract Arabian Babblers (Turdoides squamiceps) are territorial, cooperative breeding passerines in which groups consist of parents and helpers. All members of the group feed nestlings in a single nest and all group members provision at similar rates. We hypothesized that the field metabolic rate (FMR) of Arabian Babbler nestlings is related to group feeding; that is, FMR would be greater in nestlings of larger rather than smaller sized groups. To test that hypothesis, we measured FMR of 10 day old nestlings from small (2 and 3 individuals), medium (4 and 5 individuals), and large (6 or more individuals) groups. We also determined number of hatchlings and fledglings produced per group. There was an increase in body mass and FMR from small to medium-sized groups, but there was a levelling off or decrease in those parameters in large groups. That suggests that there is an optimum group number for provisioning nestlings, above which there may be a negative effect. The relationship between group size and annual number of eggs was not significant, but there was a positive and linear relationship between group size and annual fledglings production. Thus, more eggs reached the fledgling stage with an increase in group size, suggesting that larger groups are better able to defend the nest against predators.