Is that my mobile ringing ... or is it just a bird?

If your computer modem sounds a little odd - try checking the tree outside.

According to a new CD released by the British Library this week, what sounds like the search for a connection may, in fact, be a blackbird in full voice.

The CD, Bird Mimicry, is compiled from recordings held by the British Library Sound Archive which stores the world's largest collection of the sounds of nature.

Birds can mimic almost any sound, whether it comes from an animal within earshot or the noises of inanimate objects such as a squeaky farm fence, a mobile phone or a digital alarm clock.

Starlings have been known to learn the high-pitched, duo-toned screech of a car alarm. The sound archive's CD includes Sparkie Williams, a champion talking budgerigar, and the hand-reared bullfinches who were taught to whistle German folk tunes. "As the birds were taught the same tunes by different trainers, each bird sings a slightly different version - much like if two humans were whistling the same song," said sound archivist Cheryl Tipp.

Then there's the fawn-breasted bower bird in Papua New Guinea which learnt the sounds made by workmen mending a tin roof: the noise of hammering, sawing - even the rattles of a ball-bearing rolling around inside a spraycan of paint.

Mimicking sounds is an integral part of how birds learn to build up the vital repertoire of songs that they need to defend a territory or attract a mate, said Professor Tim Birkhead, an ornithologist at the University of Sheffield. "For a bird it makes absolutely no difference whether the sound is from an artificial source, from another bird or whether it comes from its dad," Professor Birkhead said. "Mimicry is the entire basis for how they acquire their songs and there are whole categories of birds that will happily incorporate other strange sounds into their songs to produce a vast, rambling repertoire," he said.

Marsh warblers and starlings are particularly good mimics and have been known to pick up and incorporate the distinctive songs of other species. "I once knew of a captive goldfinch with a very distinctive song. Within three months, the local starlings had learnt to imitate it and they were still singing the song two years after the goldfinch had died," Professor Birkhead said.

Andre Farrar, a spokesman for the Royal Society for the Protection of Birds, said that his father used to call his Jack Russell terrier with a distinctive whistle. The local starlings soon learnt to imitate it and quickly learnt how to call the dog to the bottom of the garden. "There's an evolutionary advantage to birds who can augment their songs. Females of many species choose those males with the most complex songs, so there is a biological imperative to imitate sounds," Mr Farrar said.

Perhaps the strangest bird mimic is the black-throated honeyguide of Africa, which mimics the sound of a bees' nest to attract the attention of local people. The bird then guides the humans to the hive itself to share the spoils.

But birds don't like noisy neighbours. Studies have shown that as ambient noise from towns and roads increases, so does the tendency for songbirds to move to quieter sites.

Dutch scientists showed that it was the younger and more inexperienced birds that were forced to build their nests close to busy roads. Older, more experienced birds preferred to establish their territories well away from the sound of traffic.

- INDEPENDENT