Increases in maximal capacity for thermogenesis (or Peak Metabolic Rate, PMR) are typically associated with winter acclimatization in passerines showing marked seasonal changes in cold tolerance. Thermogenic capacity also increases in spring migrant Warbling Vireos Vireo gilvus, a Neotropical migrant, relative to summer acclimatized individuals, but a similar increase does not occur in fall migrants. We tested whether migratory disposition was associated with variation in thermogenic capacity in another Neotropical migrant passerine, the Yellow Warbler Dendroica petechia, and in two passerine species migrating to mild temperate regions in winter, Yellow-rumped Warbler Dendroica coronata and Ruby-crowned Kinglet Regulus calendula. PMR was elicited by cold exposure in an atmosphere of 79% helium:21% oxygen during spring and fall migration for all species, and also during summer for Yellow Warblers. Yellow and Yellow-rumped Warblers both exhibited significantly higher thermogenic capacity in spring than at other seasons (23.3% greater than pooled summer and fall values in Yellow Warblers, 19.8% greater than in fall Yellow-rumped Warblers). For kinglets, males showed significantly higher PMR in spring than in fall (10.9%), but PMR did not vary seasonally in females. Thus, these species conform to a pattern of elevated thermogenic capacity in spring relative to other seasons, at least in the sex establishing breeding territories, suggesting that this may be a common pattern in migratory passerines. Mild temperate migrants migrate earlier in spring and later in fall than Neotropical migrants and, as a consequence, experience less variation in temperature between spring and fall migrations. Nevertheless, PMR varied similarly on a seasonal basis among Neotropical and mild-temperate migrants, despite the greater seasonal variation in temperatures encountered by Neotropical migrants. Moreover, ANCOVA on log PMR with log mass as a covariate did not demonstrate systematically lower PMR in Neotropical migrants than in mild temperate migrants for the species in this study, despite the differences in temperatures encountered during migration. This suggests that seasonal changes in PMR during migration are not associated with temperature acclimatization, but instead vary with other features of migratory patterns.