Abstract:
Animals thriving in hot deserts rely on extraordinary adaptations and thermoregulatory capacities to
cope with heat. Uncovering such adaptations, and how they may be favoured by selection, is essential
for predicting climate change impacts. Recently, the arid-adapted zebra finch was discovered to
program their offspring’s development for heat, by producing ‘heat-calls’ during incubation in hot
conditions. Intriguingly, heat-calls always occur during panting; and, strikingly, avian evaporative
cooling mechanisms typically involve vibrating an element of the respiratory tract, which could
conceivably produce sound. Therefore, we tested whether heat-call emission results from a particular
thermoregulatory mechanism increasing the parent’s heat tolerance. We repeatedly measured
resting metabolic rate, evaporative water loss (EWL) and heat tolerance in adult wild-derived captive
zebra finches (n = 44) at increasing air temperatures up to 44 °C. We found high within-individual
repeatability in thermoregulatory patterns, with heat-calling triggered at an individual-specific
stage of panting. As expected for thermoregulatory mechanisms, both silent panting and heatcalling
significantly increased EWL. However, only heat-calling resulted in greater heat tolerance,
demonstrating that “vocal panting” brings a thermoregulatory benefit to the emitter. Our findings
therefore not only improve our understanding of the evolution of passerine thermal adaptations, but
also highlight a novel evolutionary precursor for acoustic signals.
