LINDA WERTHEIMER, HOST:
You've heard the expression Bright Lights, Big City. For many people, city living can mean long hours at work and play and never enough sleep. Now a new study suggests that cities can have a very similar effect on another group of residents: birds. NPR's Rhitu Chatterjee reports.
RHITU CHATTERJEE, BYLINE: Since the 1930s, scientists have noticed that birds in cities, like robins and starlings, can keep different hours than their relatives in forests. Barbara Helm is a biologist at the University of Glasgow.
BARBARA HELM: If you walk through a forest at, say, 4:00 in the morning , it would be just dead quiet. And if you walked through the city, you would just already hear all these birds singing.
CHATTERJEE: But she says no one knew whether all this pre-dawn singing reflected a permanent change in the daily rhythms of urban birds. And that's what Helm and her colleagues decided to investigate in their study on one species: the European blackbird.
HELM: They used to be a relatively shy forest bird until about a couple hundred years ago. And now they're like a totally ubiquitous city bird. And they even in the inner business districts of cities.
CHATTERJEE: Including cities like Munich, where she and her team conducted the study. They compared the city birds with those living in a nearby forest.
HELM: This was a forest some 20 miles outside Munich.
CHATTERJEE: Helm's colleague, Davide Dominoni, is at the Max Planck Institute for Ornithology. He went out and captured six birds each in the city and in the forest. And on each bird he attached a tiny radio.
DAVIDE DOMINONI: That is just a simple radio, which gives an impulse, a radio impulse every three seconds; it's like a doo, doo, doo.
CHATTERJEE: Any changes in the strength of that signal meant that the bird was moving. An unchanged signal meant that the bird was sitting still, or asleep. So by looking at the signals around dawn and nightfall, Dominoni figured out when the birds woke up and when they went to bed. It turns out that the forest birds woke up at the crack of dawn. But their city cousins were up well before.
DOMINONI: The birds in the city of Munich, they were waking up approximately half an hour earlier than the birds in the rural forest.
CHATTERJEE: And they went to bed a good six minutes later. So in all these city birds also slept about 40 minutes less each day. And when the scientists brought back 14 city and 14 forest birds to their lab and kept them all under the same conditions, the city birds still woke up earlier, suggesting that their body clocks had become programmed to run at a faster pace.
The results of the study were published in the latest Proceedings of the Royal Society. Biologist Steve Nowicki of Duke University says this is probably a common phenomenon.
STEVE NOWICKI: I bet that what's happening to blackbirds is happening to every species that is exposed to, you know, urban disruption.
CHATTERJEE: The urban disruption, he says, is probably city lights, which mess with the body's sense of day and night. Because light controls how our and other animals' bodies calculate day length. And...
NOWICKI: Birds in particular are extremely attuned to day length.
CHATTERJEE: Nowicki says in humans bright city lights change body clocks and disrupt sleep patterns which in the long run can affect our health. But whether there are negative impacts on urban animals, that's hard to tell, he says. Blackbirds seem to thrive in cities. But other species, he says, may find it harder to handle the faster urban clocks. Rhitu Chatterjee, NPR News. Transcript provided by NPR, Copyright NPR.