City living could have a major impact on the biological clocks of humans and animals, a new study has found.
Researchers measured the circadian rhythms - the 24-hour cycle of biological activity - of urban and rural blackbirds in southern Germany.
German and Scottish researchers found the city birds woke up earlier and rested less than forest dwelling birds.
The team has raised the possibility the differences could be the result of micro-evolutionary changes.
The study, which has been published in the journal Proceedings of the Royal Society B, was carried out by Glasgow University and the Max Planck Institute for Ornithology in Germany.
A number of adult male European blackbirds were captured from Munich and a nearby rural forest.
Each bird was equipped with a lightweight radio-transmitter which monitored their daily levels of activity in the wild for 10 days before they were recaptured.
They were then kept in light-proofed, sound-insulated chambers and their circadian rhythms were measured under constant conditions.
Once the tests were complete the birds were returned to the wild.
The team said its research added "to a growing consensus" that towns and cities "have a profound effect on the internal clocks" of humans and animals.
The researchers have raised the possibility the differences in the biological rhythms could be the result of micro-evolutionary changes in response to urban phenomena such as artificial light and increased noise levels.
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