Variation in growth of nestling tree swallows across multiple temporal andspatial scales

Differences within a species in rates of growth of nestlings can be used as indicators of the quality of parental care, environmental conditions, and future success of offspring, whereas comparisons among different species ma y reflect a history of different ecological conditions or life-history stra tegies. The presesnt study examines the patterns of variation in growth in nestling Tree Swallows (Tachycineta bicolor) from across the species' range and compares Tree Swallows to other species. Growth of Tree Swallows was t ypical of other species in the family Hirundinidae. As a family, the Hirund inidae have slower growth than typical for passerines. Growth rate of speci es of Hirundinidae was not correlated with adult body mass or average brood size. Contrary to predictions, species that are double-brooded did not hav e higher growth rates, but swallow species living at higher latitudes did h ave higher growth rates than tropical species. Substantial variation in gro wth rates was observed among populations of Tree Swallows, yet the amount o f variation observed between breeding colonies only a few kilometers apart, or from the same colony in different years, was as great as that seen in p opulations separated by hundreds of kilometers. Within a population, differ ences in growth among years were correlated with temperature and food suppl y when nestlings were being raised. No correlation between climate and grow th was seen when comparing different populations. Differences between popul ations were not explained by local habitat, nor were large-scale geographic patterns evident. I used both experimental and observational evidence to e valuate the implications of short-term reduction in growth for subsequent g rowth and survival. Nestlings were slow to recover from even very short per iods of delayed growth that occur early in the nestling phase. Return of ne stlings with experimentally or naturally induced delayed growth was reduced , which suggests that short interruptions in growth may have long term effe cts on postfledging survival, even though mass at fledging is not affected.