With the proliferation of smartphones and apps, more bird-watchers are using recorded bird songs to flush out species for better viewing and photography. But the technique is controversial among some experts who say it can stress male birds that believe a recorded song signals a rival invading their territory.

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On a spring morning in North Seattle, a chestnut-backed chickadee — let’s call him Chuck — was taking care of business when he heard an alarming sound: the high-pitched song of another male.

Chuck swooped in to investigate. Perched in a hemlock, he cocked his head, listening for the intruder. Hearing no repeat, he voiced his “chick-a-dee-dee” challenge. He then flew off, paying scant attention to the gray-haired man holding an iPod-speaker combination the size of a coffee mug.

“I promise I’ll never do this to you again,” said Dennis Paulson, a veteran birder and director emeritus of the Slater Museum of Natural History in Tacoma.

Paulson was demonstrating a technique that’s hatched a flap among bird-watchers: the use of recorded calls to flush out species for better viewing and photography.

These being folks who love nothing more than tramping around with binoculars, the sparring is mostly polite. It’s a given that no one wants to harm a feather on a sparrow’s head. But the question is whether being summoned by a phantom rival may, in some cases, actually put birds at risk.

“It stresses the birds, I wouldn’t deny that for a minute,” Paulson said. “But as far as I know, it’s a very, very short-term stress.” His personal rule is to use “playback” rarely and only where birds aren’t likely to ever encounter recorded song again — deep in the woods or, just this once, his forested yard.

But for many other birders, playback has become a tool of first resort, thanks to the proliferation of smartphones and apps that can crank out tunes from every species on the planet. At the same time, birders share unusual sightings and hot spots via the Internet, which can mean the same birds are blasted over and over.

“It has gotten much more common,” said Dr. Jack Stephens, president of the Washington Ornithological Society. He recalls the days when only the most expert birders bothered to cart bulky tape players into the field. “Now, you see people get out of a car and the first thing they do is pull out a recording and start to play it on a loop.”

Like most birders, Stephens is middle-of-the-road on playback. He cringes at overuse. But, after 45 minutes of fruitless scanning on a Texas trip, a song snippet earned him a glimpse of a Swainson’s warbler, one of North America’s most secretive species.

Heard as a threat

While delightful to our ears, singing is serious for birds. Males pour their hearts out to impress the ladies. They trill to proclaim territory and keep other males away. Every strange song — whether from another bird or an iPhone — registers as a threat.

“That’s why it works,” said Sam Wasser, director of the University of Washington’s Center for Conservation Biology. “The male is going: ‘Oh, my god! There’s another bird in my territory.’ ” The trickery is most effective during breeding season.

When the sought-after bird pops out, birders can snap pictures and tick off a box on their life lists. But the consequences to the bird can include heart-pumping anxiety, exposure to predators and an undefended nest and mate.

“I’ve seen woodpeckers respond to playback from birders … and a sharp-shinned hawk comes and takes that bird out,” said Martyn Stewart, a Seattle-based wildlife recording expert.

Stewart is “dead set against” the use of playback to lure birds — yet many apps and song libraries include his recordings. “It’s ironic … but I’m really instrumental in it,” he said.

With 30-plus years of experience, Stewart easily can detect the difference between a relaxed bird and one responding to a threat. “You can hear the stress in their voice,” he said. “Birders will say there’s no harm done, but that’s because they want to justify putting a bird on their list.”

Federal biologists recently scaled back the use of recordings in spotted-owl surveys after it became clear that birds who “Whoo”-ed in reply were subject to attack by more aggressive barred owls.

May have impacts

One reason birders are so split on the use of playback is that there’s little evidence pro or con. But a handful of studies suggest the practice is not entirely innocuous.

Ordinary life already is tough for birds, especially during breeding season, said UW biologist Eliot Brenowitz, who studies brain wiring and bird song. In some species, males become accustomed to the voices of their neighbors, which makes them more likely to be alarmed by an unfamiliar, recorded call, he said.

UW professor emeritus John Wingfield found testosterone levels increased up to tenfold in male song sparrows confronted with taped songs. They remained revved up for one to two days. “These males will continue to spontaneously sing and patrol their territory,” Wingfield said. “They get very aggressive and attack other birds.” And they were distracted from parental duties, such as feeding chicks.

Elevated testosterone also may suppress birds’ immune systems, though that link is unproved, he said.

Wingfield’s years of field research helped persuade him to give up the use of playback in his recreational birding. Daniel Mennill, who discovered playback can have romantic fallout for male birds, still makes judicious use of the technique.

“In moderation, I don’t think it’s going to have negative effects,” said the University of Windsor, Ontario, biologist.

When Mennill and his colleagues bombarded male black-capped chickadees with recorded calls to simulate an aggressive rival, they discovered females were listening, too. Lady birds whose mates came out on the losing end of the singing contests were much more likely to engage in “extramarital” flings. Other males also took advantage, encroaching on the turf of neighbors who appeared weak.

“There’s a message in there for bird-watchers,” Mennill said. “It’s conceivable that [aggressive use of playback] could influence the bird’s reproductive output for that year.”

Banned in some places

Recorded birdcalls are banned in some parks and refuges, including the national parks. To many old-school birders, it’s just considered lazy. But curmudgeons aside, playback is here to stay, said ornithologist, artist and bird-guide author David Sibley.

After creating a bird-identification app, Sibley drew up a list of suggested guidelines for the proper use of recorded calls. Chief among them is to never target threatened or endangered species, to use only short snippets of song and to stop after a few minutes.

If the instant gratification that playback can provide draws more people to bird-watching and environmentalism, many birders argue that’s a good thing. In some cases, luring a bird into the open with playback can be less disruptive than a group of people stomping around in the bushes, Sibley said. Even birders who just sit still can be disruptive. “You might end up sitting near a nest.”

When alone, Sibley prefers to watch birds behaving naturally. He says he pulls out the handheld sound system only when he’s leading field trips and doesn’t want to disappoint.

“I find it sort of distracting,” he said. “I end up spending more time messing around with the device, starting and stopping, setting the volume, and less time actually looking at birds.”

Sandi Doughton: 206-464-2491

or sdoughton@seattletimes.com