Urban noise 'killing baby house sparrows'

The UK's house sparrow population has been declining since the 1970s

Noise in urban areas could be increasing the mortality rate among young house sparrows, a study has suggested.

Researchers say the noise could stop adult birds hearing the hunger calls from their dependent offspring.

In their study, the team found that birds nesting in noisy areas were less effective at feeding their chicks as those that nested in quieter places.

The findings have been published in the journal Plos One.

Scientists from the University of Sheffield reached their conclusion after carrying out a study on Lundy, a 445-hectare (1,100-acre) island located 19km (12mi) off the North Devon coast.

Co-author Julia Schroeder explained that the project happened more-or-less by chance.

"When I first went to the island, which is very remote and quiet - apart from gulls and shearwaters - I entered a barn and it was very loud," she recalled.

The barn contained an electricity generator, yet sparrows were still choosing to nest in the building, so Dr Schroeder wondered whether the conditions affected the songbirds.

"I found that there was a reduced fitness - a reduced reproductive output from the nest boxes located in the noisy area," she told BBC News.

So she decided to test her findings against classic hypotheses on how noise could affect birds.

"The main hypothesis regarding breeding output is that it affects mate choice decisions," she explained.

Steep decline

However, the study's findings did not fit the existing hypotheses.

"In our case, we saw that the birds did not feed the chicks as well as the birds in the quiet area - this was a novel idea that had not been shown before," Dr Schroeder said.

"Obviously, chick provision is strongly linked to chick survival because if they do not get fat then they die."

Noise seemed to interrupt the communication between the young birds and their parents.

"The only difference we found from normal behaviour was in the provisioning behaviour," she observed.

"Chicks that were reared in the noisy barn were lighter when they fledged.

"So this is why we have said that we think that the provisioning behaviour of females is a factor."

Between the mid-1970s and 2008, the UK's sparrow population declined by 71% - with some of the sharpest declines occurring in towns and cities.

Dr Schroeder and the team suggested that the noise from the generator on Lundy was comparable to car noise in urban areas.

"There are lots of studies on great tits and urban noise, but these tend to focus around mate choice, where the male advertises its quality to the female.

"But the idea that the communication between parents and offspring could be affected in cities is fairly new."

In 2007, another study by researchers at the University of Sheffield <link> <caption>published in Biology Letters</caption> <url href="http://rsbl.royalsocietypublishing.org/content/3/4/368.abstract" platform="highweb"/> </link> found that urban-based robins were choosing to sing and communicate at night in order to avoid noise during the day.

Until then, it had been thought that birds were singing at night because they were being disturbed by light pollution.

Dr Schroeder added that it could be that other songbird species could also be affected in a similar way as the sparrows on Lundy.

She observed: "Many songbirds communicate in a similar way so it is possible that other species could be affected too."