Urban blackbirds pay price for tuning into city rhythms

City life can take its toll, even on birds, judging by new research that shows blackbirds living among humans wake up earlier and sleep less – leading to more health troubles and shorter lives, it has emerged.

"We found that the rhythms of urban birds in the wild differ significantly from their forest counterparts," said Dr Barbara Helm, of the University of Glasgow's institute of biodiversity, animal health and comparative medicine.

“On average, they began their daily activities around 30 minutes before dawn, while forest birds began their day as the sun rose. The city birds ended their days around nine minutes later, meaning they were active for about 40 minutes longer each day,” she said.

Circadian rhythms
The study into the circadian rhythms of urban blackbirds living in Munich in southern Germany compared with their rural cousins living in forests elsewhere in Bavaria was jointly carried out by the Scottish university and the Max Planck Institute.

Adult male blackbirds were first captured in the city and the forests before they were fitted with a lightweight radio transmitter that monitored their movements 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, without any environmental information that could serve as a “clock”.

“In this way, each bird’s own, internal rhythm could be tested. Once the tests were complete the birds were returned to the wild,” researchers wrote in a paper published by the Royal Society in London.

Davide Dominoni of the institute said: “For songbirds, early risers may have an advantage in finding a mate and thus a greater chance of successfully producing offspring and passing along their chronotype to the next generation. “

Other research has shown that a bird’s chronotype – a measure of whether it is a night owl or an early morning creature – “are highly heritable, so the process of natural selection could mean that city birds are evolving to favour early risers”, researchers found.

Disrupted sleep
Research on the effects of urban living on humans has so far shown that it can lead to disrupted sleep and increased examples of depression and diseases including obesity and some types of cancers.

Excited by the findings, Dr Helm said: “Our work shows for the first time that that when sharing human habitats, a wild animal species has a different internal clock. There seems to be a different beat to city life.”