A heat-sensitive songbird’s risk of lethal hyperthermia increases with humidity
Data files
Sep 09, 2025 version files 61.52 KB
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NLiddle_Biology_Letters_Data_and_Script_GDrive_submission.zip
56.98 KB
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README.md
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Abstract
Increasingly frequent and intense extreme heat events are making heat-related avian mass mortality events more common, but the role of elevated humidity as a contributing factor remains unclear. Here, we quantified the effect of humidity on risks of lethal hyperthermia for Blue Waxbills (Uraeginthus angolensis), the species most common among the victims of South Africa’s first documented heat-related mortality event involving wild birds. We quantified body temperature (Tb), metabolic heat production, and evaporative heat loss at air temperatures (Tair) approaching and exceeding normothermic Tb in dry (1.1 ± 0.9 g m⁻³) and humid (21.3 ± 0.4 g m⁻³) air. The humid treatment was associated with significant reductions in evaporative cooling capacity and overall heat tolerance, with maximum tolerable Tair ~2 °C lower (45.7 °C) compared to the dry treatment (47.9 °C). A model of end-of-century exposure for the waxbills reveals that elevated humidity will increase the risks of lethal hyperthermia 3- to 7-fold in some parts of southern Africa.
Dataset DOI: 10.5061/dryad.tht76hfbd
Description of the data and file structure
Files are all associated with Blue Waxbill (Uraeginthus angolensis) physiological response variables to two flow-through respirometry experiments. Experiment or protocol 1 involved waxbills (n = 10) being subjected to dry air (~0 g m⁻³) and a stepped air temperature profile starting at 28°C and incrementally increasing until birds reached their thermal endpoints. Experiment or protocol 2 involved waxbills (n = 10) being subjected to humid air (21 g m⁻³), and a stepped air temperature profile starting at 34°C and incrementally increasing until birds reached their thermal endpoints. The objective was to determine how birds physiologically respond to high temperatures under dry and humid conditions, to extrapolate whether humidity increases lethal hyperthermia risks during heatwaves in humid environments.
Files and variables
File: NLiddle_Biology_Letters_Data_and_Script_GDrive_submission.zip
Description:
1 R script and 11 .csv files associated with the study titled, “A heat-sensitive songbird’s risk of lethal hyperthermia increases with humidity”. The data files are all derived from the original file, titled “BWall.csv”, and are provided for easy running of the script. All variables are the same as those in BW_all. The script is divided into two sections: 1) Linear mixed effects models and 2) t-tests on maximum response variables across the two protocols, as well as plot code.
File: BW_all.csv
Description: All measured physiological responses with increasing air temperature across the dry and humid air respirometry protocols. There are no blank values in the provided files.
Variables:
[1] "Date" "protocol" "Bird" "Sex" "Mass" "Tcab"
[7] "Ta" "Tb" "VCO2" "VH2O" "waEWL" "msVCO2"
[13] "msH2O" "waRMR" "msRMR" "EHL" "EHL.MHP" "Treatment"
Date: yyyy/mm/dd format.
Protocol: describes whether subjects belonged to the dry or humid air respirometry treatments.
bird: unique ID associated with each bird. IDs are all prefixed with “BW”, then “D” or “H” for dry or humid protocol, respectively, followed by an integer denoting the number of birds sampled.
Sex: the biological sex of the bird. Possible values - “male”, “female”, “unknown”, “unknown (M?)”
Mass: mass of the bird in grams (g)
Tcab: calibrated air temperature of the metabolic chamber in each stepped air temperature profile in °C. This is the temperature manually input into the system during experiments by the observer.
Ta: actual measured air temperature (°C) inside the enclosed metabolic chamber housing the bird.
Tb: bird body temperature (°C) as measured by a PIT tag and downloaded from a receiver
VCO2: measured carbon dioxide (CO2) production (ml/min) from each bird as measured from excurrent air flows from the metabolic chambers.
VH2O: measured water (H2O) production (mg/min) from each bird as measured within the excurrent air flows from the metabolic chambers.
waEWL: calculated evaporative water loss (g/hr) produced from each bird, as calculated using VH2O.
msVCO2: calculated mass specific arbon dioxide (CO2) production (ml/g/min) from each bird per Tcab
msH2O: calculated mass specific ater (H2O) production (mg/g/min) from each bird per Tcab
waRMR: calculated resting metabolic rate (W) from each bird for each bird per Tcab
msRMR: calculated mass-specific resting metabolic rate (W) from each bird per Tcab
EHL: calculated Evaporative Heat Loss from each bird per Tcab
EHL.MHP: calculated Evaporative Heat Loss/Metabolic Heat Production from each bird per Tcab
Treatment: similar to “Protocol” by denoting the approximate absolute humidity was per protocol. Possible values- “0 g.m⁻³” and “19 g.m⁻³”
Code/software
File: Comparing dry and humidity.r
Script is R-compatible, and can be run in RStudio Version 10.0.26100.4061. All input files are comma-delimited files (.csv), which can be opened and inspected in Microsoft Excel or other spreadsheet-compatible programs and software.
Required packages:
library(lmerTest)
library(MuMIn)
library(lme4)
library(car)
library(sjPlot)
library(sjmisc)
library(ggplot2)
library(jtools)
library(tidyverse)
library(ggpubr)
library(rstatix)
library(dplyr)