Danish ornithologists say that birds, especially Starlings, have begun incorporating the sound of a ringing cellular phone into their own songs. So far, reports of wireless warbling have been restricted to Copenhagen, where birds seem to favor Nokia's classic ring tone.

Birds imitating sounds produced by technology is nothing new. They choose simple tunes to reproduce. The standard ring tone on a phone usually comprises any combination of nine tones. And the tunes themselves don't typically contain harmonies, which are made by playing multiple musical tones at the same time.

Usually, birds copy what they hear the most. Birds in rural areas have added the sound of horses whinnying, lawn mowers and even chainsaws to their repertoires. In cities, birds have added car alarms, the warning beep of a truck backing up and police sirens to their calls, experts say.

Ornithologists expect birds in other cities where cell phone penetration is high to begin adding ring tones to their tunes.

Imagine the possible confusion, says Andrew Smith, spokesman for London-based Royal Society for the Protection of Birds. A single ringing phone can already cause a room of mobile phone owners to reach for their pockets.

A few Starlings armed with a Nokia tune crowing on a crowded city block "could bring a place like San Francisco to a stand still," Smith said.

Starlings, which are found in many areas of the world, in addition to mockingbirds, catbirds, brown thrashers and others, constantly look for new tunes for their songs, which are sung to attract the opposite sex, experts say.

The longer the song, the more macho the bird appears to be, according to Allison Wells, director of outreach for the Cornell Lab of Ornithology.

"It makes the males who sing that much more attractive," she said.

But if some mischievous bird manages to indeed force an entire city sidewalk of pedestrians to check on their phones, there is some revenge on the way.

Companies have started offering bird calls as ring tones, Smith said.

"I wonder what would happen if these birds hear those ring tones and think it's a potential mate," Smith said.