Birds know how to keep cool

A bulbul. In the absence of sweat glands, birds pant to release heat. Photo by Jagpreet Luthra

Keeping bowls of water are the best way humans can help birds during summer. Photo by Jagpreet Luthra

A male house sparrow. Open bills also help thermoregulation. Photo by Jagpreet Luthra

Holding the wings away from the body, a kite is exposing the surface area and letting the wind sweep away the heat. Photo by Jagpreet Luthra

A female sunbird. Nest-building and parenting add to the heat stress. Photo by Jagpreet Luthra

A tailorbird. A bird’s heat tolerance threshold is 40°C. Photo by Jagpreet Luthra

High summer spells trouble for birds. The heat tolerance threshold of a bird is the same as its body temperature — around 40 degree Celsius. However, anything above that can be lethal, and birds need to release the heat to survive.

In the absence of sweat glands, the two most important ways birds dissipate heat are through panting and open beaks. An open bill lets the hot air outside sweep over the wet mucus membranes of the mouth and throat, leading to evaporative cooling. Panting is another way birds get rid of the excessive heat. The respiration rate of a house sparrow, for instance, goes up from 57 per minute at 37 degree Celsius to 160 per minute at 43 degree Celsius. However, both panting and open beaks also cause rapid water loss or dehydration. Scientific studies suggest that a bird experiencing peak temperature during a hot summer day cannot survive for more than a couple of hours.

Birds also lose heat through exposed skin, the reason why they often hold their wings away from the body on a hot day, letting the air sweep away the heat. Light-coloured birds turn their lightest parts towards the sun on a hot day to reflect the heat. The other things birds do to beat the heat are exactly what we do: they drink more water, bathe or dip in water, rest in the shade, and avoid foraging and chirping in the afternoon. So, they are smart; still, humans can make the summer easier for birds — at least in their backyards — by simply keeping bowls of clean water for them.