Urban Blackbirds Have Faster Circadian Rhythms Than Rural Relatives
June 19, 2013

Urban Blackbirds Have Faster Circadian Rhythms Than Rural Relatives

Brett Smith for redOrbit.com - Your Universe Online

For years we have known about the differences between city slickers and country bumpkins, but a new study from the Max Planck Institute in Germany has shown that the different environments can have different effects on an organism´s natural biological rhythms.

Along with ornithologists from the University of Maine and the University of Glasgow in Scotland, the Max Planck researchers studied the circadian rhythm of both urban and rural blackbirds in southern Germany. They found that the city birds had faster and less reliable internal clocks than their country brethren, according to their report in Proceedings of the Royal Society B.

“The daily cycles of activity and rest are based on biological rhythms which have evolved as an adaptation to the rising and setting of the sun,” said Barbara Helm, a lecturer at the University of Glasgow´s Institute of Biodiversity Animal Health and Comparative Medicine.

“Our tests were designed to benchmark the internal rhythms of the birds under controlled conditions and to determine a link to the birds´ chronotype in the wild,” Helm said. “Chronotype is a measure of an individual´s consistent timing relative to environmental factors, i.e., its relative ℠morningness´ or ℠eveningness´.”

For the study, the researchers captured both city and forest birds. Each bird was equipped with a radio transmitter that monitored the animal´s daily activities for 10 days before the birds were recaptured again. They were then kept in light- and sound-proofed chambers to prevent them from knowing the actual day while researchers again measured the birds´ circadian rhythms.

After completion of the tests, the birds were returned to the wild unharmed.

“We found that the rhythms of urban birds in the wild differ significantly from their forest counterparts,” Helm said. “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," Helm said. “In constant laboratory conditions, urban birds´ circadian rhythms were clearly altered, running faster by 50 minutes than forest birds and being clearly less robust. There seems to be a different beat to city life. City clocks were also less persistent, especially in the business district.”

One previous study has shown that circadian rhythm can be disrupted by depression in humans. Other studies have tied circadian rhythm to obesity and some diseases, such as cancer and diabetes.

“We´d be keen to find out the costs and benefits of modifying biological rhythms in blackbirds and other animals commonly found in our cities,” Helm said. “This may help us to better understand the challenges of coping with urban life.”

The researchers theorized that natural selection could be behind the shift in the urban birds´ internal clocks, as previous research has shown that chronotypes are highly inheritable.

“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,” said study co-author Davide Dominoni, of the Max Planck Institute.

“The speed of urbanization is accelerating around the world, but we don´t have anything close to a complete understanding of the effects of urban living on humans and animals,” he added.