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Tree swallows: Research has shown the high volume of city life threatens the survival of birds by making it harder for nestlings to hear their parents

The constant drone of traffic is threatening the survival of baby birds and putting populations at risk of collapse, scientists have warned.

Research has shown the high volume of modern city life makes it harder for nestlings to hear their parents. This puts them at risk of going hungry. And makes them deaf to danger from predators.

Canadian researchers said: 'We usually associate declines in animal populations with our physical destruction of habitat but the noise we make is another threat we can't ignore.'

The team from Dalhousie University, in Nova Scotia, studied tree swallow chicks that were still too young to fly and so dependent on their parents for food and protection.

The nestlings were played recordings of calls made by parent birds returning when with food and when warning about an approaching predator.

Some of the recordings had a quiet background – others were noisy.

Faced with background noise, the chicks frequently failed to beg for food when they should.

They also mistook calls warning them of danger for ones saying food was on the way.

This stopped them from taking cover from potential predators, an Acoustical Society of America conference heard.

However, parent birds seemed to be oblivious to the problem. The study showed they didn't change their calls to compensate for increasing background noise.

Researcher Andy Horn said that the ubiquitous noise of traffic, building sites and other human activity could break the vital line of communication between parent and nestling.

He said: 'The likelihood that nestling songbirds will survive until leaving the nest depends largely on how well they are fed by parents and how well they escape detection by predators.

'If nestlings are to be fed without being eaten themselves, they must beg readily to parents but avoid begging when predators are near the nest.'

Confusion: Faced with background noise, the chicks frequently failed to beg for food when they should. They also mistook calls warning them of danger for ones saying food was on the way

He added that while all background noise isn't man-made, traffic noise or building work tends to last for longer than the natural sounds such as wind or rain.

The study is far from the first to look at the impact of noise on bird life.

Previous studies have found that great tits in the noisiest parts of the Netherlands have higher-pitched tunes than those in more peaceful parts.

In Sheffield, some robins have abandoned their traditional dawn chorus and sing at night instead.

And in San Francisco, sparrow songs have become more shrill, likely to allow them to be heard above the growing rumble of traffic.

A higher pitch also helps prevent the tweets and chirps from being distorted when they bounce of buildings, boosting the odds that the notes reach the ears of potential mates.