DOI: 10.5061/dryad.6wwpzgncf
title: Data from: A challenge of warmer temperate winters: Long-term exposure to rain in cold temperatures drives higher thermogenic investment in a captive songbird

description: 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.
description: # Data from: A challenge of warmer temperate winters: Long-term exposure
 to rain in cold temperatures drives higher thermogenic investment in a
 captive songbird Dataset DOI:
 [10.5061/dryad.6wwpzgncf](https://doi.org/10.5061/dryad.6wwpzgncf) ##
 Description of the data and file structure In this experiment data was
 collected over the course of four months on 48 individual birds to
 determine how cold rain impacts thermogenic capacity and avian physiology.
 Birds were randomly assigned treatments of cold rain, cold dry, warm rain,
 and warm dry, and were assigned an ID number for the course of the
 experiment. Metabolic measurements were measured three times throughout
 the experiment, food intake & activity rates were measured daily and
 then averaged weekly, and morphometric data were collected once per week. 
 ### Files and variables #### File: Msum_and_BMR_w_food_and_activity.csv
 **Description:** Month and its interaction with weather variables were
 included as fixed effects to detect seasonal changes in Msum and BMR. We
 include log transformed mass in all metabolic models. ##### Variables \*
 Date: Date of metabolic measurement \* Month: Month of metabolic
 measurement (Measurements in late december and early january were combined
 as January measurements) \* Bird ID: Individual ID \* Temperature:
 Temperature treatment of Cold or Warm \* Precipitation: Precipitation
 treatment of Rain or Dry \* Daylength: Daylength treatment of Short or
 Long \* Gonadal Sex: Sex of Individual \* Mass: Mass of individual (g) \*
 Abdominal Fat: Abdominal fat score (scale of 0-5) \* Furnicular Fat:
 Furnicular fat score (scale of 0-5) \* Bairlein Muscle Size: Muscle size
 (scale of 0-3) \* MSUM: Summit metabolic rate (mL O2 min ^-1^) \* BMR:
 Basal metabolic rate (mL O2 min ^-1^) \* Food Intake: Average daily food
 intake (g) \* Activity: Average daily activity rate (total number of
 movements per day) #### File:
 Weekly_Data__Activity__Food_intake__Fat__Muscle__Mass.csv
 **Description:** Experiment week and its interaction with weather
 variables were included to detect changes across time. Individual ID was
 included as a random effect. GAMMs were used to account for nonlinearity
 in food intake and daily activity across weeks. ##### Variables * Week:
 Week of the experiment \* Temperature: Temperature treatment of Cold or
 Warm \* Precipitation: Precipitation treatment of Rain or Dry \*
 Daylength: Daylength treatment of Short or Long \* Bird ID: Individual ID
 \* Gonadal Sex: Sex of Individual \* Food Intake: Average daily food
 intake (g) \* Activity: Average daily activity rate (total number of
 movements per day) \* Abdominal Fat: Abdominal fat score (scale of 0-5) \*
 Furnicular Fat: Furnicular fat score (scale of 0-5) \* Subcutaneous Fat:
 Subcutaneous fat score. Sum of Abdominal fat and furnicular fat (scale of
 0-10) \* Bairlein Muscle Size: Muscle size (scale of 0-3) #### File:
 Wet_Tissue_Mass__Enzyme_Activity.csv **Description:** We included BMR and
 Msum measurements from the February sampling date to determine if
 metabolic traits were associated with wet mass of heart, pectoralis,
 liver, intestine, kidney, gastrocnemius, brain and lung. Body size (keel
 and tarsus measurements) determined by a PCA was used to control for size
 differences amongst individuals in the categorical fixed effects models.
 ##### Variables: \* Month: Month of metabolic measurement (Measurements in
 late december and early january were combined as January measurements) \*
 Bird ID: Individual ID \* Temperature: Temperature treatment of Cold or
 Warm \* Precipitation: Precipitation treatment of Rain or Dry \*
 Daylength: Daylength treatment of Short or Long \* Gonadal Sex: Sex of
 Individual \* Body Size: PCA values from keel and tarsus measurements upon
 capture \* Mass: Mass of individual (g) \* Abdominal Fat: Abdominal fat
 score (scale of 0-5) \* Furnicular Fat: Furnicular fat score (scale of
 0-5) \* Bairlein Muscle Size: Muscle size (scale of 0-3) \* MSUM: Summit
 metabolic rate (mL O2 min ^-1^) \* BMR: Basal metabolic rate (mL O2 min
 ^-1^) \* Heart Mass: Wet heart mass (g) \* PM Mass: Wet pectoralis muscle
 mass (g) \* Liver Mass: Wet liver tissue mass (g) \* Intestine Mass: Wet
 intestine mass (g) \* Lung Mass: Wet lung mass (g) \* Liver CS Activity:
 Liver tissue citrate synthase activity (units min ^-1^) \* Heart CS
 Activity: Heart tissue citrate synthase activity (units min ^-1^) \* Pect
 CS Activity: Pectoralis muscle citrate synthase activity (units min ^-1^)
 \* Pect HOAD Activity: Pectoralis muscle HOAD activity (units min ^-1^) \*
 Heart HOAD Activity: Heart tissue HOAD activity (units min ^-1^) \* Liver
 HOAD Activity: Liver tissue HOAD activity (units min ^-1^) \* Brain Mass:
 Wet brain mass (g) \* Kidney Mass: Wet kidney mass (g) \* Thigh Mass: Wet
 thigh mass (g) Note: "NA" means data are not available. ##
 Code/software All statistical analyses were conducted in R (version
 2023.10.31). Linear models, linear mixed models (“lme4” R package) and
 general additive mixed models (“mgcv” R package) fit by restricted maximum
 likelihood were used to evaluate dependent variables. Plots of dependent
 variables and model residuals were visually checked and verified to be
 normally distributed using skewness and kurtosis. We used a = 0.05 for
 assessing significance and the top models were selected based on the
 lowest AIC values when comparing between full and reduced models.