Data from: A challenge of warmer temperate winters: Long-term exposure to rain in cold temperatures drives higher thermogenic investment in a captive songbird

Long-term cold exposure induces many endotherms to invest in metabolic
heat production, but how precipitation impacts thermogenic capacity in the
context of different thermal conditions is largely undescribed in animals.
In this study, songbirds (red crossbills; Loxia curvirostra) were held in
warm (21 °C) or cold (6 °C) temperatures and either dry or rain
precipitation treatments while experiencing a more northern or southern
latitude photoperiod. We hypothesized that individuals experiencing winter
rain would increase investment in thermogenic capacity, metabolic
machinery, and catabolic enzymes to cope with increased thermogenic
demands. Food intake and activity were monitored weekly, summit (Msum) and
basal metabolic rates were measured in November, January, and February,
and tissues were collected at the end of the study. Individuals held in
cold rain treatments achieved the highest summit metabolic rate and had
higher food intake, subcutaneous fat, heart mass, and metabolic enzyme
activities. Further, birds in dry conditions showed slight disinvestment
of Msum in late winter, while birds in rain treatments maintained
thermogenic investment. Our results suggest that cold rain induces
increased investment in thermogenic capacity across the winter season.
Thus, rain may offset the potential thermal benefits that warming winters
would otherwise provide to small-bodied endotherms.