Birds sing louder to be heard

Just as humans shout to be heard when in raucous settings, bluebirds also alter their songs in response to increases in the nearby background noise such as loud traffic, research says.

Although it has previously been shown that birds in noisier areas tend to sing differently than those in quieter surroundings, it was not clear whether birds were able to make vocal adjustments in real time.

In the study, the researchers found that the male bluebirds altered their songs as noise levels intensified, making 'real-time' adjustments in order to produce songs that are both louder and lower-pitched.

The results suggest that birds are able to perceive increases in noise and respond accordingly.

"This certainly seems to be the case with bluebirds," said lead researcher Caitlin Kight from the University of Exeter in Britain.

The researchers recorded songs produced by 32 male bluebirds, and analysed two from each male -- those produced during the quietest and loudest period of ambient noise -- to check whether males change their songs between these two conditions.

As background noise increased, male bluebirds produced songs that were louder and lower-pitched, the findings showed.

This suggests that the birds are able to both perceive and respond to increases in noise. This enabled them to produce songs that were more likely to be heard by potential mates or rivals.

The findings appeared in the journal Integrative and Comparative Biology.