Effects of food supplementation. (A) Nestling growth from the onset of the manipulation (day 2 posthatching) to the end of supplemental feeding (day 5 posthatching). On both days, nestlings were weighed before the treatments were applied. (B) Total food provisioning by both parents (deliveries per hr) in relation to begging vocalizations 4/5 d posthatching (vocalizations per nestling per hr), immediately following the feeding treatment. (C) Total food provisioning in relation to begging vocalizations (as in B) 7 d posthatching, two days after the supplemental feeding had ended. (D) Nestling prefledging mass. All panels depict least-squares means ± SE. Black symbols depict experimental (Exp) nests (nestlings fed food dissolved in water), open symbols depict control (Con) nests (nestlings were fed water only), and grey symbols depict unmanipulated, natural (Nat) nests that were not supplemented.