According to researchers, the calling songs of birds in urban centres are now radically different to those in rural environs. City birds have developed their songs in order to ensure they are heard over the noise of urban life. Birds in cities now sing shorter, higherpitched and faster-paced songs than their rural counterparts.

The findings were made by two Dutch researchers who studied bird calls in 10 urban and 10 rural sites across Europe. While Ireland did not feature in the study, experts here have said that Irish birds could be expected to have developed in identical ways to urban birds in other northern European cities, and have warned that these results could explain why some birds have disappeared from Irish cities in recent years.

Hans Slabberkoorn and Ardie den Boer-Visser, both of Leiden University, recorded the songs of the great tit in rural and urban sites. They found that noise from traffic, construction work and increased human activity had caused city birds to adapt their songs.

In their study, published in the December issue of Current Biology, the researchers warned that birds use song to attract mates, ward off rivals and warn other birds of danger.

If urban noise was drowning out these songs, the future of the species as urban dwellers would be in doubt, they concluded.

The recent findings backup a theory known as acoustic-adaption hypothesis, which states that some aspects of the vocal variety of animal communication sounds are shaped by the environment. However, this is the first time such a study has been conducted on birds.

According to Dr Gareth Dyke of UCD's Department of Zoology, the study is hugely significant in terms of Irish birds. Birds found in Irish cities are the same as those found in any other city in northern Europe, and so this study would help to explain why some species have flourished in an urban environment whereas others have been driven out of Irish cities, he said.

Previous studies have shown that growing urbanisation has greatly affected bird behaviour in Ireland, said Dyke.

As well as changing bird habitat, city living has altered the social structures of birds. Just as humans in urban areas have become more detached from their communities, birds in cities also live more solitary lives and do not live in the communal structures of rural birds.