Rising temperatures make life harder for desert birds
For birds living in hot, dry environments, rising temperatures make it increasingly difficult to obtain sufficient food. This was the finding of a study by researchers from the Percy FitzPatrick Institute of African Ornithology (University of Cape Town) and Macquarie University. These results suggest important long-term consequences: the decreased ability to find enough food during hot conditions potentially threatens the persistence of populations in the face of global warming.
The researchers worked with a habituated, free-living population of Southern Pied Babblers (Turdoides bicolor) - birds that live in southern Africa’s Kalahari region. By observing these birds, they were able to collect detailed data on how foraging behaviour and body weight changed depending on air temperature. The study was carried out at the Pied Babbler Research Project located close to the border between South Africa and Botswana. Here, Dr Amanda Ridley has habituated a population of individually identifiable babblers that are trained to hop onto a scale so that their weights can be recorded without having to catch them repeatedly.
The research was inspired by recent mass die-offs of birds and bats during heat waves in Australia. These die-offs suggest that some animals already live close to their physiological limits and may be impacted by only small increases in maximum temperatures. What the researchers wanted to understand was what happens to birds as temperatures approach these thresholds where their lives potentially become threatened by heat stress.
The study found that on hotter days babblers foraged less efficiently, partly because they were trying to forage while at the same time panting and spreading their wings to keep cool. As a result, on days when temperatures exceeded 36°C, the babblers failed to gain enough weight during the day to compensate for the weight they lost during the night. These results suggest that birds in arid-zone ecosystems may already be walking a tightrope with respect to their water and energy budgets. The Kalahari has become hotter since the 1960s, and is predicted to become hotter still in the coming decades. If future heat waves are longer and more intense, the consequences for birds and other animals could be severe indeed.
This research, supported by the DST/NRF Centre of Excellence at the Percy FitzPatrick Institute, has just been published in the international journal Global Change Biology.
IMAGE: Dr Mandy Ridley with one of the habituated babblers (Photo: Alex Thompson)