A heat-sensitive songbird’s risk of lethal hyperthermia increases with humidity

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 hypertherm..., , # A heat-sensitive songbird’s risk of lethal hyperthermia increases with humidity

Dataset DOI: [10.5061/dryad.tht76hfbd](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 envi...,