City birds crying louder to talk above city din
Researchers in The Netherlands discovered that urban great tits in the noisiest areas sing at the highest frequencies.
They believe the city birds have changed pitch to counteract the deep background rumble caused by cars, planes and roadworks.
Like other song birds, male great tits sing to mark their breeding territories and attract mates. Birds that cannot make themselves heard are unlikely to breed. An ability to adapt to city din is therefore essential.
Hans Slabbekoorn and Margriet Peet recorded the songs of 32 male great tits in the Dutch city Leiden.
Each bird had a repertoire of between three and nine different song types.
The researchers found that the average minimum song frequency was “significantly correlated with ambient noise” and ranged between 2.82 kilohertz and 3.77 kilohertz.
“Noisy territories were home to great tit males whose songs had a high average minimum frequency,” the two scientists from Leiden University wrote in the journal Nature.
“Birds in quiet territories sang more notes that reached the lowest frequencies measured for the population,” it said.
The birds were not simply choosing territories that suited their singing styles. Great tits learned their songs and were known to adjust them during interactions with their neighbours.
“They appeared to be adjusting song to territory instead of territory to song,” the scientists said.
