When the going gets hot, most creatures head for shade. But not white-winged doves. They spend the summer in the Sonoran desert where they are perfectly content perched on saguaro cacti, even when the mercury tops 50°C. As Andrew McKechnie explains, there's only one-way to stay cool in those conditions; by evaporation, and white-winged doves are particularly good at it. Most animals manage to keep their temperature down either by evaporating water across the skin, or by panting as the temperatures soar. But McKechnie and Blair Wolf wondered how good the birds are at adjusting to rapid temperature changes. Could they modify their water loss mechanisms quickly when the temperature rose? Acclimating the birds to hot and cool environments,McKechnie tested how well they fared as he turned up the heat, and found that the birds are champions of the cool(p. 203).
McKechnie headed into the sweltering desert where he had no problems netting 14 doves ready to return to the lab. Back in Albuquerque, he segregated the birds, placing half in a temperate room at 21°C, while the remaining birds were released into a searingly hot room where the temperature topped 43°C every day. After three weeks, McKechnie began testing the doves' heat tolerance in a respirometer, where he could track both their water losses and metabolic rates over temperatures ranging from 35°C to 45°C.
As the temperature in the respirometer rose the differences between the birds were instantly clear. The cool-acclimated birds had to work much harder to stay cool, resorting to panting to keep their temperature down, while the hot-acclimated birds seemed relatively untroubled as the temperature hit 45°C. And when he measured the amounts of water that the two groups lost across their skins, almost 80% of the hot-acclimated birds' total evaporative water loss was across their skin, while the birds that had acclimated to the lower temperature only lost 53% of their water across the skin. The hot-acclimated birds had made their skin more permeable to lose water and keep cool.
Measuring their metabolic rates as the temperatures rose, McKechnie also realised that it took much less effort for the hot-acclimated doves to keep their temperature down, than it did for the birds used to cooler climes; which wasn't too surprising. The cool-acclimated birds had resorted to panting as the conditions got stickier, and so their metabolic rate rose much more then the birds that were used to the heat.
McKechnie admits that he is surprised that the hot-acclimated birds were able to increase their ability to lose water across the skin so quickly. Not only would they need to increase their peripheral blood pressure to squeeze fluid out of the blood and across the skin, but they'd also have to alter the skin's permeability by altering the lipid content. He adds that staying cool might not be quite so straight forward back in the desert, where the humidity is very variable, but McKechnie is confident that the bird's fantastic adaptability lies at the heart of their unconventional choice of summer home.