New Collaboration: Do small birds use torpor?
Updated: Jul 23, 2020
Dr Yaara Aharon-Rotman at the University of New England recently invited me to join her on a nifty project looking at torpor in small birds. Torpor is like a kind of temporary hibernation where animals slow down their thermoregulation and metabolic processes, going into a kind of stand-by mode to save energy. We know that lots of small mammals do it, as do some bats. There is some evidence that small birds do it but not a lot of work has been done on them. There is also no clear pattern that would indicate why or when these birds might switch into torpor mode as a survival strategy. You would think it would be a simple relationship with how cold it gets at night but, as always, nature is more complicated than that. Yaara and I worked together on migratory geese and what they get up to on an important wetland in China and I jumped at the chance to work with her again.
We were targeting two species. We have some preliminary data from White-throated treecreeper (Cormobates leucophaea) that suggest they may show some level of torpor. We are also looking at Eastern yellow robin (Eopsaltria australis) and nobody has looked at torpor in this species before. We just spent the last week catching birds in a beautiful nature reserve called Imbota near Armidale, NSW.
We caught them using mist nets and ground traps loaded
with tasty meal worms with the help of the excellent Dr Christa Beckman from Western Sydney University. To help us lure the treecreepers down from the trees (where they spend a lot of time creeping) and into the nets we had the help of a stunningly rendered model of a treecreeper called Gal (a Hebrew name that can be male or female, because our model was gender fluid depending on what paint job they had). We were attaching radio transmitters to them The radio transmitters weigh less than 0.35g and are glued directly onto the skin of the bird. We expect them to fall off within two to three weeks (hopefully not sooner!).
The transmitters have a very clever mechanism of telling the temperature of the bird. As we listen to the regular beeping of the radio signal to locate a bird, the interval between beeps changes with the body temperature of the bird. So, once calibrated correctly, we can tell how warm the bird's skin is by listening to the beeps. This means we can tell if the bird is still actively keeping itself warm or if it has slipped into torpor mode. We would expect that torpor would happen at night when the bird is roosting and we can't be out there all night wandering around the bush with yagi antennae. So we have a little automatic recorder that listens for the beeps and notes the intervals between them. Every night we go out and try to get as close to our roosting bird as possible and place a logger nearby to pick up the signals. Ideally we can place one logger in the right place so it can pick up signals from several birds. We also put out some little temperature loggers at or near the tree where they are roosting so we can get a more accurate idea of what the local temperature conditions are.
This week we tagged four of each species and the data is already rolling in. Representing the treecreepers we have Adam, Bernie, Christoff and Dougal and on team robin we have Waldo, Xena, Yolo and Zorro. Hopefully the transmitters will stay on long enough and the birds will get up to something interesting while they sleep. Yaara hopes to deploy more transmitters later this year and hopefully we will have a publication to talk about not long after that.