Fig. 1. Relationships between daily temperature range and thermogenic capacity (M_sum) differ among five Junco taxa assayed in the field.

a Map of sampling sites for field measurements color-coded by taxon, following color scheme in b–f and plotted in R with package mapdata⁸⁷. b–f Taxon-specific relationships between M_sum and daily temperature range (averaged over the 8 days prior to capture), while controlling for differences in body mass. Each dot represents an individual (n = 335). Sample sizes for each taxon are listed at the top and the slope (β; in ml O₂ min⁻¹ °C⁻¹) of each relationship is shown in the lower right corner. Sampling occurred during the breeding season (filled circle) or nonbreeding season (open circle). Lines fit from glm (M_sum = M_b + Taxa × T_{d_range}) using mean M_b for each taxon. Source data are provided in the Source Data file.