In the wild, many animals generate body heat when they move which they need to get rid of to avoid overheating. Out of all the various ways that animals move, flight requires the greatest amount of energy, leading to one of the highest rates of body heat production. To lower their body temperatures, birds get rid of heat though their head, feet and the top of their wings. Losing the heat that they produce while flying is especially important for birds when considering the rapidly warming global temperatures. But how important each body area is for dissipating heat before, during and after flight has not yet been determined for any bird species. This question led Agnès Lewden and colleagues from the University of Leeds, UK and Institut Universitaire Europèen de la Mer, France to determine how yellow-collared lovebirds (Agapornis personatus) dissipate their body heat before, during and after flight.
To test which body areas were important for getting rid of the excess heat the lovebirds generate while flying, the team studied seven lovebirds that were trained to fly in a wind tunnel located at the University of Leeds. The researchers randomly flew each lovebird 11 times and used a thermal camera to continuously record the lovebirds. Each recording started with the birds standing on a wooden perch before the birds flew, during flying and ended when the birds were resting again on the perch after landing. Following all flight trials, the researchers analysed the thermal videos and measured the surface temperature of the birds’ head (including the eyes and bill), the legs (including the feet), the body (including the front, back and the top of the wing), and – while the lovebirds flew – the underside of the wings (which was visible only during flight). The team then used mathematical modelling to calculate the different forms of heat loss (i.e. convection – heat loss due to air moving past the bird; radiation – heat lost to the air through infrared rays; and conduction – heat loss through physical contact) for each part of the birds before, during and after flying.
Lewden and colleagues found that the birds’ heat dissipation while flying was 12-times higher than before their flight and 19-times higher than after they landed again, likely resulting from the greater amount of body heat produced during flight and their need to get rid of it. When the researchers looked at each body area separately, the team uncovered differences in how and when they dissipate heat. Specifically, before flying, body heat was mainly dissipated by the head and body but during the flight, the birds dissipated the majority of their body heat (85.9%) through the underside of the wings, despite this body area only making up 26% of the birds’ surface area. This shows the importance of the underside of the wings in keeping birds cool. The researchers also discovered that the lovebirds dissipated heat differently depending on whether they were perched or flying. The birds lost heat mainly through infrared rays (radiation) before and after their flights. However, heat loss during flight was primarily through air rushing past the underside of the wings (convection), likely reflecting the change in the lovebird's body posture during flight.
Overall, Lewden and colleagues showed how lovebirds dissipate body heat through different body areas before, during and after flight. Their research is especially important when considering the rapidly warming global temperatures and suggests how other bird species may lose excess heat in hotter temperatures. Further research is needed to determine if other species cool themselves like lovebirds do before, after and on the fly.
