Fig. 1. Timeline (A) and diagram (B) for behavioral observations in experiment 1. (A) Immediately after nestlings were captured from their nest was body mass recorded. Upon arrival at the lab, nestlings were fed wax moth worms (total worm weight scaled to chick body mass) and left undisturbed for 35 min. After the quiescence period, nestlings were fed with a worm injected with peanut oil with or without corticosterone. Behavior was observed for the following 25 min. After collecting a blood sample and taking measurements of growth, nestlings were returned to their nest. (B) Nestlings were placed in a natural nest within a small box taped onto a larger observation box. A small slit in the observation box allowed the experimenter to tap the nest box in place without being seen by the subjects. A video camera placed next to the observation box was aimed at the nest box. An electric body warmer was placed underneath the observation box to keep the nestlings warm.