Preformative molt extent of Cardellina warblers increases with breeding latitude and migration distance

The New World warbler genus Cardellina consists of 3 long-distance migrants breeding in boreal and montane forests (Canada [C. canadensis], Wilson's [C. pusilla], and Red-faced [C. rubrifrons] warblers) and 2 sedentary species living in montane forests of northern Central America (Red [C. rubra] and Pink-headed [C. versicolor] warblers). We quantified wing-feather molt extent and frequency of wing-feather replacement of the preformative molt for all 5 species, then used these data to test whether the preformative molt extent is influenced by breeding latitude and migration distance. Our dataset consisted of molt cards from a published dataset and 2 online photographic libraries. Due to the small number of sampled species, we applied a 3-way approach: (1) comparison of molt extent among species using a post hoc pair-wise t-test; (2) comparison of molt extent between migratory and sedentary species using phylogenetic ANOVA; (3) PGLS regression of molt extent on breeding latitude and on migration distance. Contrary to our prediction, sedentary species had significantly lower molt extents, and a linear, although not significant, increase with breeding latitude and migration distance. We propose that loss of migratory behavior allowed Red and Pink-headed warblers to allocate resources to the synthesis of more energy-costly pigments. Received 26 April 2022. Accepted 8 December 2022.