Weight and feather growth of nestling tree swallows

Abstract

Six models were tested for weight and feather growth of nestling tree swallows (Iridoprocne bicolor). The logistic model, with an asymptotic weight A of 22.4 g and a growth-rate constant K of 0.51 day−1, was most appropriate for weight growth. Observed curves for individual birds were of diverse shape and some lacked weight recession. Growth of primary feather 9 and rectrix feather 6 followed the Gompertz model, with A and K values of 80.9 and 49.6 mm, and 0.21 and 0.20 day−1, respectively. Fitting of the models to feather length was complicated because growth curves for individual birds did not coincide in time, and fledging occurred before completion of growth. Long nestling times were associated with slow weight and feather growth, and A and K were consistently negatively correlated. The variation of A, K, and nestling time among broods ranged from 49.2 to 95.1%, and brood size could not account for much of the observed variability. Presumably, various nest-box variables and weather conditions as related to the age of nestlings are important. Primary and rectrix growth were similar and closely linked but apparently unrelated to weight growth. Growth of feather vanes was closely linked to feather growth. Birds that failed to fledge had depressed weight, feather, and vane growth. Weight growth and recession seem to be particularly well suited for investigating natural and man-made environmental stresses.