Thermoregulatory strategies of songbird nestlings reveal limited
capacity for cooling and high risk of dehydration
Abstract
Developing young are particularly sensitive to environmental challenges,
often with life-long consequences, but the risks of climate warming
during this period are not well understood. To quantify the
physiological effects of increasing temperatures for developing
endotherms, we measured metabolic rate, water loss, and heat dissipation
behaviours between 25-45°C in nestlings of a free-living songbird. The
thermoneutral zone ranged from 33.1–42.3°C – higher and narrower than
adults – and metabolic rate increased sharply above and below this
range. Water loss was constant below 33.5°C, above which it increased
sharply, when nestlings also drooped their wings to lose heat. Despite
nestlings initiating panting (p50) around 40°C, water loss was never
sufficient to dissipate metabolically produced heat, indicating poor
cooling capabilities. Our data show that while developing young appear
relatively tolerant to higher temperatures, they are at a high risk of
dehydration and hyperthermia, with limited ability to mitigate these
risks of increasing temperatures.