Male great tits respond to the calls of other males by calling back rapidly, and thus overlapping the incoming call with their own.

ECONOMIST: Parasitology: The song does not remain the same | The

Huge Himalayan vultures wheel eye-level with the road, while tiny tits inhabit a range of vegetation, from conifers and cedars to broadleaved oaks and rhododendrons.

BBC: Apple harvest in the Himalayan foothills

That suggests hunger and parasites affect song in different ways a fact that tits are, no doubt, acutely aware of when they size each other up.

ECONOMIST: Parasitology: The song does not remain the same | The

Mr Ricketts said trust staff had cleared litter after "numerous events" at the site, which is also home to about 60 species of birds including kestrels and long-tailed tits.

BBC: Cambridge raves 'damaging' reserve wildlife

Scientists also recorded countryside great tits and found they sang at a lower pitch and, in turn, city birds found the rural droll difficult to understand, the study found.

BBC: Birds in cities 'singing louder'

The singing was played back to rural male tits during the breeding season when they are at their most aggressive, but there was a "slower and weaker" response than normal from the countryside birds.

BBC: Birds in cities 'singing louder'