To survive searing heat, desert birds have developed adaptations to stay cool; they sweat, vibrate their throat muscles to flutter air over the moist surface of their throat, or pant like a dog, although panting is the least efficient mechanism for remaining cool. Yet, songbirds, which make up over half of all bird species, are only able to resort to panting to keep their temperatures down, so how have they managed to colonise even the hottest regions on Earth when keeping cool is quite costly for then? One group of researchers from Australia and South Africa had noticed that zebra finches that live in arid Australian deserts also switch to singing when panting to prevent themselves from overheating. In addition, the scientists discovered that parents that twittered while panting when sitting on their eggs gave their young a better start in the hot environment. Anaïs Pessato from Deakin University, Australia, and her colleagues sought to understand whether singing while panting helped the birds cool off more quickly while also saving water in their dry habitat.
To solve this mystery, the team recorded when wild zebra finches began silent panting or singing while panting, and how long they continued, across temperatures ranging from 35°C up to 44°C. To investigate how quickly singing while panting had an effect on the birds’ ability to regulate their temperature, the team compared the animals’ water loss, energy use and body temperature during the run up to, and after, normal panting and the same period before and after the birds took up tweeting while panting. In addition, they investigated how the birds coped over longer periods by measuring the proportion of time spent panting, or singing while panting, at 35, 40, 42 and 44°C.
As soon as the birds began normal silent panting, the team noticed that they were using more water to cool down, although they were also, unexpectedly, using a lot less energy. However, when the birds began singing while panting, their water loss rates increased even more, going up by 4%. Because vocal panting increases the amount of water being evaporated, it allows the birds to cool faster, which allows them to survive at hotter temperatures, albeit at the cost of increased water loss. In fact, the birds that vocally panted for over half of the 14 min experiment had an almost 60% greater chance of enduring the hottest temperature, 44°C. Although water is a scarce resource in the desert, using it to avoid overheating in hot temperatures is worth it for these desert birds.
In addition, the team noticed that individuals always began panting silently at around the same body temperature and they also spent the same proportion of time panting silently and vocally. Each bird also tended to switch to singing after an initial period of regular panting that was specific to themselves, suggesting that zebra finches may be able to adjust when they implement this alternative form of panting in order to combat the rising temperatures they will likely encounter as a consequence of climate change.
Pessato and her team have found that singing while panting helps songbirds keep cool in the Australian desert, which allows them to survive sizzling temperatures up to 44°C. However, melodic panting comes at a cost: the birds have to consume more water, which is an expensive commodity for desert species. This newly discovered adaptation to cope with hot temperatures, and how it is different in birds within a population, will help us to understand how species may survive as climate change continues.