Welcome to the third and final instalment of the: Keeping Cool in the Delightfully Warm Summer Series. Previously we explored how Mammals and Reptiles have overcome the challenges of the warm weather associated with summer in the beautiful African Lowveld.
What has been a continuous theme with Mammals and Reptiles, is that organisms both big and small are constantly trying to balance their core body temperatures – Birds are no different.
Birds do not sweat and instead have to rely on other ways to stay cool. Either by using metabolic heat exchange or using the surrounding environment, they have to endure tough conditions to avoid overheating, which when reaching certain levels, can lead to illness or even death. Birds are no different to mammals in that they produce their own metabolic heat and have adaptations and methods to counteract their ‘warm-blooded’ heat regulation system.
Lets explore the possible ways that birds are able to Cool their bodies:
Drinking and Submerging in Water
Essentially, when it’s warmer, birds drink more water because water acts as a natural cooling agent and by staying well hydrated, birds can use water for evaporative cooling. This is easy for birds associated with water such as water birds and waders.
However, those that live further afield such as Raptors may be seen standing in water to cool the bare scaly skin, bellies and vents which cool the blood effectively.
Other birds with small feet and short legs that cannot make a quick getaway from predators at the edge of the water, prefer not to stand in the water but will plunge and dive from a perch to completely soak themselves. This is seen with the Kingfishers, Bee-eaters and Drongos which allows for an efficient option for cooling down while minimising the risk.
Countercurrent heat exchange
Possibly the most important adaptation that the bird kingdom has utilised. When temperatures rise to extreme levels and the core body temperature reaches a critical level, an involuntary mechanism kicks in, known as Gular fluttering. Characterised by rapid vibrations of the throat skin, the bird will open its beak to allow for more effective airflow which allows air to pass rapidly over the moist mouth membrane and the tongue which results in the evaporative cooling of the blood in the brain.
This is an effective cooling mechanism but comes at the huge cost of expeditiously losing water and energy. However, if a bird cannot prevent its body temperature from rising to the upper lethal temperature (ULT) then the brain will lose the ability to control metabolism and hyperthermia will set in resulting in rapid death.
Vultures and Storks may appear, from time to time, to have a layer of ‘whitewashing’ covering their legs. When the weather is warm, they defecate on their legs and use faeces as an agent to keep cool. The initial evaporation begins the cooling process. The faeces is usually a whitish colour and in doing so continue to help reflect the solar radiation from the sun which then maintains the temperature of the bird.
Overheating of Eggs and Chicks
Various bird species use the warmer summer months with abundant food supply to breed efficiently. The hotter conditions can lead to overheating of eggs and chicks, especially for birds that nest in exposed sites, such as high up in trees with little cover, or exposed on the open ground. The temperature of eggs can be regulated through incubation, however, it is more difficult to protect chicks from the harsh sun once they have hatched. In order to provide shade, certain birds will ‘mantle’ over the chicks with their wings spread out.
Occasionally, a pair of storks will bring stomach-fulls of water to the nest, which they regurgitate over their young as a cooling shower and in extreme cases, some herons cool their chicks in a less hygienic way by defecating over them in a relieving but undignified way.
There you have it, the Keeping Cool during the Delightfully Warm Summer series has come to an end. I hope you enjoyed reading about how animals and birds are able to balance their body temperatures out in the wild and the amazing ways in which they are able to do so. Maybe we could use some of these tricks, but certainly not all of them.