Researchers spy on forest birds’ sex lives with tiny tracking devices

York biology Professor Bridget Stutchbury is hooking birds up with tiny radio-transmitter backpacks in order to spy on their comings and goings – with some surprising results.

bird with radio back packIn her current study of forest birds, Stutchbury and a team of York researchers from the Department of Biology, Faculty of Science & Engineering, found new evidence to support the idea that not only are these birds non-monogamous – but that females are “sneaking around” on their mates, too.

Left: Bird with tiny backpack radio transmitter

“The early literature emphasized that male birds are the cheaters of the species,” says Stutchbury, York’s Canada Research Chair in Ecology and Conservation. Stutchbury was among the first to find that females are making clandestine trips to hook up with other males, too.

Bridget StutchburyThe backpacks, which are smaller than a button, are attached to birds with a harness around their legs. Stutchbury carries a radio receiver, which enables her to pick up the signal from each of these tiny transmitters, allowing her team to map out the location of each bird at any given time.

Right: Bridget Stutchbury

“With the use of these tracking devices, we were able to start drawing arrows on the map, and the arrows show a precise overlay of who is cheating on who,” says Stutchbury.

She uses DNA paternity testing on offspring to ascertain whether these trysts actually result in copulations. In the case of the Acadian Flycatcher – one of the birds she’s currently tracking – she found that almost half of the nestlings were illegitimate. Males who had a nesting female on their own territory nevertheless travelled throughout the forest looking for other female partners.

For the first time, Stutchbury’s team tracked the activities of both male and female birds within couples, or pairs, of Wood Thrush.

“When the females sneak away to have sex with other males, their spouses follow them. It’s astounding,” Stutchbury says. “The male stays within 10 metres of his mate almost the entire time. It’s really hard to not think of this in human terms.” This close mate-guarding seems to work in this species, since only a handful of nestlings were illegitimate.

The findings, part of a decade-long study of forest birds’ behaviours and habitats, offer a rationale as to why they tend to crowd in large forested areas and avoid smaller patches.

“Large forest patches mean that females have more males to choose from,” Stutchbury says. “In the long run, it provides the rationale for conservation of large forest patches – that we can’t save endangered or threatened species of birds by merely improving the quality of smaller patches.”