Humans forcing birds to sing louder
Ever get the feeling when you're lying in bed on a Sunday morning that the birds in your area are getting louder and louder?
Well, you may be on to something.
American researchers have discovered bird songs are getting louder to compete with increasing traffic noise levels.
Using archived tapes from the 1950s of sparrows in one area of San Francisco, and comparing it to recordings from recent years, scientists found that today's birds have a far more high pitched song than decades ago.
Comparing the birds' songs to the increasing sound and traffic levels in the same area, Professor David Luther found that today's more shrill sparrows also sing fewer songs or dialects.
He says only one dialect now dominates in the area, and it is generally the highest pitch song.
"It's the really low hum where almost all of this human-made noise is - in this very low bandwidth", he told the Daily Mail.
"The birds can often sing at the top end of that low bandwidth and, if there's no traffic around, that's just fine."
"But if they're singing and there is noise, the lowest portion of that song gets lost, and the birds can't hear it."
As a result, birds in noisier areas have adjusted their songs to make sure they're being heard.
Similar studies in the Netherlands and Berlin found birds in built up areas are louder than their neighbours in quiet forests.
Berlin's nightingales reportedly sing up to 14 decibels louder when surrounded by more noise.
