Do pigeons sweat? If not, why not?
鈥� Only mammals have sweat glands 鈥� so no, pigeons do not sweat. Nor do mammals such as cats, whales and rodents, which have lost most or all of their eccrine sweat glands 鈥� the ones that we use in shedding heat 鈥� while birds never developed them. In sweat-free mammals the kidneys deal with the excretory functions of sweat, and flushing or panting is how they cool themselves down. As another example of evaporative cooling, an over-hot cat not only pants but also moistens its fur with saliva.
Bird skins are dry. However, as birds, including pigeons, have body temperatures that are generally several degrees higher than those of mammals, they do not need the same capacity to lose heat.
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鈥淏ird skins are dry. When they need to lose heat, they can raise their down feathers鈥�
When they do need to lose heat, they can raise their down feathers to cool the skin by ventilation; to conserve heat they flatten them. Beyond this, panting through open beaks causes evaporative cooling: hence the Afrikaans expression: 鈥淪o hot the crows are yawning鈥� (So warm dat die kraaie gaap).
Finally, on very hot days, many kinds of birds, including pigeons, enjoy a bath.
Jon Richfield, Somerset West, South Africa
鈥� Storks, cormorants and vultures indulge in urohydrosis: they literally wet and thus cool themselves by urinating down their legs. As birds do not urinate and defecate separately, everything comes out together, which makes bird droppings very watery. The heat required to evaporate this liquid from the surfaces of the legs cools the blood, carried close to the surface of the legs by a network of veins.
Before condemning these birds for their unappealing party trick, it is worth adding that bird droppings contain uric acid, making it an effective antiseptic 鈥� very useful for vultures that spend a lot of their time trampling over rotting carcasses.
Mike Follows, Willenhall, West Midlands, UK