Birds are not the only animals experiencing massive declines in populations. Rising temperatures and heat waves, in particular, have been blamed for killing humans and animals. In fact, a new review article published in Physiology mentioned that globally, heat is “a significant natural killer of humans, with the first decade of the 21st Century seeing a 23-fold increase in human casualties from heat waves compared with the 1990s.” If current predictions hold true, it may become too hot in some regions of the world for humans to spend significant amounts of time outdoors.
If these areas are not habitable by humans, with the technology to comfortably remain indoors, what about the animals? For example, an extreme heat wave in Australia occurred in November 2018 killing off around 23,000 gray-headed flying foxes. They simply cannot evaporate water well enough to tolerate increases in body temperatures above 40°C. In contrast, larger animals, like humans, camels, felids, canids, kangaroos, and ungulates are able to tolerate short bouts of heat through well-adapted thermoregulatory processes.
While some animals certainly succumb during heat waves, others are able to tolerate the heat. Birds in particular have higher body temperatures (37– 44°C) than mammals. The temperature at which birds begin to experience tissue damage and an inability to regulate body temperature is therefore higher (43– 46°C) than mammals. Similarly, echidnas spend the day in logs and can tolerate environmental temperatures up to 42°C.
Hyraxes and elephant shrews can also tolerate elevations in body temperatures up to 40– 42°C and antelope ground squirrels can tolerate up to 43°C. Small insectivorous bats are even more impressive with the ability to tolerate body temperatures up to 45°C. But rock doves (i.e. pigeons) and common poorwills have an even more impressive ability to tolerate environmental temperatures up to 62°C (143°F). Rock doves really are ‘rock stars’ because when they are acclimated to the heat, they can breed even when temperatures outside reach 60°C! Birds thermoregulate primarily through panting as well as gular fluttering (see below):
Stay cool everyone!
Andrew E. McKechnie, Blair O. Wolf. The physiology of heat tolerance in small endotherms. Physiology. 34: 302–313, 2019. doi:10.1152/physiol.00011.2019
Categories: Comparative Physiology