Most passerines use fat to fuel migration and pause at stopover sites to rest or refuel. Moreover, during spring migration, en route to breeding grounds, passerines may deposit “excess” fat as either insurance against unpredictable environmental conditions or in anticipation of breeding. We analyzed the energetic condition of Hermit Thrush (Catharus guttatus), Swainson’s Thrush (C. ustulatus), and Veery (C. fuscescens) during spring and autumn migration at the Braddock Bay Bird Observatory (Rochester, New York, USA). We used path analysis to determine if the “spring fatter” or insurance hypotheses could help explain some of the variation in energetic condition in Catharus thrushes by designing and analyzing biologically plausible models of the potential effects of season, capture date, hour captured, and age on energetic condition during stopover. While path models differed among species and seasons, capture (or arrival) date was the strongest predictor of energetic condition; contrary to the insurance hypothesis condition increased with date during both seasons for all species. Hour of capture predicted much less variation in condition but was consistently positive (when significant). In long-distance migrants (i.e., Swainson’s Thrush and Veery), less experienced or young migrants exhibited better condition than adults regardless of arriving later, which was revealed by including a direct path between age and condition and an indirect path mediated via capture date to control for potential differences in arrival timing related to age. Despite being closely related, we found only a few patterns in common among Swainson’s Thrush, Hermit Thrush, and Veery. We suspect differences in phenology, flight, morphology, and migratory strategy may play a significant role in the differences among these species.

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