Tape-luring depletes birds' energy
In the forests of Ecuador, Plain-tailed Wrens nest in bamboo thickets, singing complex and continuous melodies. Residing nearby are Rufous Ant-pittas, small, secretive birds that hop like thrushes and whistle in mossy forests. Together, their songs fill parts of the South American Andes.
Birders often seek out birds like the wren and ant-pitta using 'playback' or tape-luring – recordings of bird songs played in the field to draw the birds out into the open. However, new research suggests that this technique may well harm the birds.
Using the emphatic sounds of both bird species, a Princeton University researcher has – for the first time in peer-reviewed research – examined the effects of birders' playbacks in the wild. In PLOS One, he shows that playback has potentially negative consequences, especially in terms of birds' energy.
"Playbacks would be harmful if a species becomes stressed, expends energy, or takes time away from other activities to respond to these recordings," said J Berton C Harris, a postdoctoral fellow at Princeton University, New Jersey, USA.
Working in a southern Ecuadorian biological reserve, Harris studied the effects of both single and repeated playback on the wren and the ant-pitta. In the first trial, he introduced single playbacks to 24 groups of wrens and 12 groups of ant-pittas, and along with David Haskell from the University of the South in Tennessee, he monitored both species for an hour after playing a five-minute, self-recorded song.
Harris' results show that, after the single playbacks, both wrens and ant-pittas sang more often, and tended to repeat these songs more often after listening to the playbacks. This could be harmful to the birds, Harris said, if it deprives them of energy. "Birds could be wasting their time and energy by responding to non-existent intruders. When male birds respond to birdwatchers' playbacks to defend their territories, they may spend less time caring for their nestlings, experience higher levels of stress hormones or be subject to a romantic coup from other males while away from their mates."
In the second part of the study, Harris and Haskell monitored the effects of daily playback on groups of Plain-tailed Wrens. Like the first experiment, he played the birds' song once for five minutes, recording the birds' responses for one hour; this was done daily for two-and-a-half weeks.
Although the vocal response was strong for the first 12 days, the wrens eventually habituated and stopped responding, suggesting that playback has minimal effect on them. One group of wrens, seemingly uninterested, even built a nest near a playback site. Harris says this behaviour should suggest that scientists should consider birding activity when selecting research sites, so that results aren't biased.
"Birders are ardent conservationists and they want to minimise their impact while observing secretive birds," Harris said. "They promote environmental conservation by funding ecotourism infrastructure, especially in developing countries where tourism can provide local people alternatives to habitat exploitation. Unfortunately, as evidenced by this research, they may also have a negative effect on ecosystems."
Harris suggests that future studies be conducted in order to better understand how playback may affect other aspects of a bird’s life.
"Studies of the effects of playback on bird reproductive success have not yet been done. And until such studies are available, it'd be wise for birdwatchers to be cautious of the negative effects. For example, it might make sense to minimize the use of playback with endangered species or in areas that host a lot of birdwatchers."
With tape-luring being the first resort of many birding visitors to the Neotropics, it may be that a little more stealth or patience is needed by observers for the sake of conservation.