In Sturt National Park, near Tibooburra in central Australia where temperatures can range from freezing to nearly 50°C, there lives a small bird with a white back, forked tail and - as we've just discovered - a very clever strategy to survive its extreme environment.
Authors
- Alice Barratt
PhD Candidate, Hawkesbury Institute for the Environment, Western Sydney University
- Christopher Turbill
Associate Professor, School of Science and the Hawkesbury Institute for the Environment, Western Sydney University
The white-backed swallow (Cheramoeca leucosterna) is a type of passerine - the largest group of birds, comprising 60% of all bird species.
Scientists have long thought these birds incapable of deep torpor - a controlled state of reduced body temperature that saves energy and has been found in many animals in the northern hemisphere, where winters are more severe.
But our new paper , published today in the journal Current Biology, shows otherwise.
Understanding how animals cope with extreme conditions
Animal physiologists have long seen the value of studying animals in extreme conditions to understand their survival strategies.
In the past, however, field instruments were cumbersome or delicate and studies were mostly limited to artificial conditions in the laboratory.
This was a problem for several reasons.
First, in captivity wild animals are often stressed and don't tend to exhibit their full capabilities . Exposing captive wild animals to extreme conditions is also logistically difficult and an animal welfare concern.
But more recently, technological advances allow us to measure the physiological responses of animals when they are exposed to extreme conditions in the wild.
Tracking birds to their burrows
Biologging involves attaching electronic devices to animals that can record key traits such as movement, body temperature and energy expenditure. It is providing a fascinating window into the natural lives of animals.
Technological advances have meant these devices have become miniature in recent years. This has greatly expanded the species scientists can study in the wild and provides an exciting opportunity to challenge long held assumptions based on lab-based studies - including about torpor.
Our team set out to investigate the white-backed swallow, which has been the subject of some intriguing reports over the years.
For example, during cold and wet winter periods, observations as old as 1936 have reported finding the birds in their sandy burrows during the daytime that appeared in a torpor-like state : "inert, nestling into each other as if to escape from the bleak winter's day".
Over the winters of 2023 and 2024, we used miniature (400 milligrams) temperature sensing radio transmitters to study the thermal physiology of these swallows in Sturt National Park - the traditional lands of the Wongkumara, Wadigali, and Malyangapa peoples.
We tracked tagged birds to their burrows at night and set up autonomous data logging units nearby to record their body temperature data.
Following a tenuous radio signal on foot across the desert was spectacular on a clear starry night. But sometimes it was also tiring and intimidating.
After that, we trusted our data logging units to collect the steady radio pulses emanating from the resting birds. From these we obtained their body temperature, and therefore their potential use of torpor.
We had two major inland rain events in winter 2024, leading to local flooding. This meant we were unable to access our field site. So we waited it out in the local campground, hoping our trusty loggers were still recording data while enduring the unusually chilly nights.
An extraordinary discovery
As the land dried out, we returned to find something extraordinary.
During and after these extreme rain events, the birds remained in their burrows even during the daytime. And they entered deep and long bouts of torpor - far exceeding what passerine birds were thought capable of.
Such torpor is presumably crucial for these in-flight foragers to survive when wet and cold conditions suppress the activity of flying insects.
More generally, our discovery of torpor use by a passerine bird suggests that this strategy is not limited to hummingbirds, nightjars and their relatives.
Instead, it could be a more widespread adaptation for survival across the diversity of birds.
A new wave of discoveries
Our finding adds to a growing number of recent discoveries revealed by biologging about the thermal adaptations of birds and mammals when faced with extreme conditions.
In 2024, for example, we found that even the largest of bats, the flying foxes (Pteropus species), are capable of using torpor during cold winter conditions that pose a risk of starvation.
In contrast, during summer, when flying foxes can be exposed to extreme heat events, our biologging data has shown they employ controlled increases in body temperature. This adaptation reduces the costs of shedding heat and helps to avoid lethal dehydration.
These data are essential for us to understand how animals survive extreme weather events, which are becoming increasingly common and severe with a warming climate.
The authors would like to acknowledge Justin Welbergen, Ben Moore and Anthony Hunt for their contribution to the research.
Alice Barratt receives funding from Western Sydney University, Hawkesbury Institute for the Environment and the Australian Bird Study Association.
Christopher Turbill receives funding from the Australian Research Council, and the Australian Commonwealth and New South Wales government.
