Researchers use thermal cameras to detect roosting birds
Where do small birds sleep? Mostly in trees is the short answer, but as so often occurs in ecology, there is more to the story…
If you were a bird, a few critical things might influence where you choose to spend the night. First and foremost, you don’t want to be eaten by a predator! And, if you want to get some rest, you can’t rely on alertness, speed and agility to escape owls or tree-dwelling mammals… So, concealment might be important. Second, you want to minimise your exposure to the elements. Smaller bodies burn kilojoules a lot faster than larger bodies, and cold winter nights can take a heavy toll on energy reserves so a thermally buffered location will also be desirable.
“For an activity that takes up a very substantial portion of a bird’s life, and where choices can mean the difference between life and death, we know surprisingly little about the ecology of sleep in birds” said co-author Rohan Clarke.
What little we do know is intriguing – for example within large communal roosts, complicated hierarchies exist where dominant birds take position at the centre of the roost - the warmest and safest position - while subordinate birds must take their chances at the periphery. While it’s relatively simple to investigate these behaviours in species that roost in large groups, it is far more challenging to even detect individuals that roost alone.
In an attempt to overcome this challenge, researchers from Monash University have been using infrared thermography, i.e. a thermal camera/scanner, to locate roosting birds of a wide range of species.
‘Thermal cameras measure heat emission. The difference in signal strength between an animal and the vegetation around it means that we can detect birds in total darkness. Another benefit is that the birds typically remain asleep, which means that this technique creates very little disturbance’, reports William Mitchell, lead author of the study.
To ensure that the technique worked, researchers carried out bird surveys during the day in an Australian woodland, and then repeated the same surveys at night using a thermal camera. They then compared detection rates of the two methods. 21 of 22 species that were commonly detected during day surveys were also found roosting at night.
“To date, we’ve recorded simple traits such as height and visibility of roost sites but this method really opens the door to dig deeper into the nocturnal behaviour of diurnal birds’ said Rohan Clarke.
“While there are some limitations, it’s great to get proof of concept for this method. We were able to quickly and efficiently detect roosting individuals for most species in our bird community with minimal disturbance” concludes William Mitchell
This research was recently published in The Journal of Field Ornithology:
Mitchell, W. F., and Clarke., R. H., 2019. Using infrared thermography to detect night-roosting birds. Journal of Field Ornithology. https://doi.org/10.1111/jofo.12285.