In her current study of forest birds, Stutchbury and a team of York researchers found new evidence to support that not only are these birds non-monogamous – but that females are “sneaking around” on their mates, too.

“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.

Right: A radio-tagged Hooded Warbler; the tag rests on its back.

The 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.

“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 they are 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.

Their findings, part of a decade-long study of forest birds’ behaviours and habitats, offers 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."

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For more information, contact:

Melissa Hughes, Media Relations, York University, 416-736-2100 x22097/mehughes@yorku.ca