By DAVID DERBYSHIRE

Last updated at 08:38 27 February 2008

Call of the wild: A starling

Birds are becoming more musical after having their brains altered by gender-bending chemicals released into the environment, research shows.

Scientists say they have the first hard proof that female hormones from the contraceptive pill and hormone replacement therapy are finding their way into the food chain and dramatically changing the behaviour of birds in the wild.

They found male starlings exposed to oestrogen spent more time singing and sang more complex songs than other male starlings.

The Cardiff University team looked at the effect of the pollutants on starlings foraging for earthworms at a sewage treatment works in the South-West of England.

Starlings' songs form a key part of their mating ritual.

To their surprise, Dr Katherine Buchanan and colleagues found that female starlings preferred the more elaborate songs of the "feminised" male birds exposed to the hormone.

They discovered that the region of the brain that controls songs in starlings - the "high vocal centre" - was much bigger in contaminated birds.

Their study, reported in the journal Public Library of Science One, did not look at the effect of the oestrogen on the birds' fertility.

Past studies have shown that oestrogen in sewage outlets is changing the sex of fish and causing males to produce eggs.