How do female Red-winged Blackbirds allocate food within broods?

Abstract

Nestlings communicate with parents via begging, but what does begging signal and how do parents allocate food to their nestlings? We tested the signal-of-need (SoN) and signal-of-quality (SoQ) hypotheses for nestling begging in the Red-winged Blackbird (Agelaius phoeniceus) by attempting to determine whether begging is negatively (SoN) or positively (SoQ) condition dependent, and by attempting to identify the attributes of nestlings that parents use to allocate food within broods. We quantified begging by its mean intensity (scale 0-7) and mean duration and parental allocation by the number of times each nestling was fed. We found that the intensity and duration of begging were not correlated with nestlings' size (estimated by body mass and tarsus length), condition (estimated from the residual of mass regressed on tarsus length), age, sex, or testosterone concentration, so begging did not appear to be negatively or positively condition dependent. A generalized linear model showed that mean intensity of begging, body condition, and log testosterone concentration were significant predictors of the number of feedings. These results are consistent with parents using begging intensity and nestling quality, but not long-term need, to allocate food within broods. © The Cooper Ornithological Society 2013.