How City Living Changes the Biological Clocks of Birds
Apparently human beings are not the only creatures who can end up getting less sleep when exposed to the bright lights and excitement of the big city.
According to a new study comparing urban birds to their country cousins, birds from the city "started their activity earlier and had faster but less robust circadian oscillation of locomotor activity than forest conspecifics."
In other words, birds living in the hustle and bustle of a 24-hour city run on a different biological clock than birds in peaceful woodlands.
The study, performed by scientists from Glasgow University and the Max Planck Institute for Ornithology in Germany, and just published in Proceedings of the Royal Society B, involved two groups of adult male European blackbirds. One group was captured in a rural forest; one came from the city of Munich.
The birds were fitted with radio transmitters and their daily habits were observed in the wild for 10 days. Then each group was also monitored in a controlled laboratory setting, where they were insulated from light and sound (don’t worry, the blackbirds were then released back to their home environments).
The two groups exhibited marked differences in their patterns of waking and sleeping, adding to the evidence that city life has "a profound effect on the internal clocks" of humans and animals, one of the researchers told the BBC:
Dr Barbara Helm, from Glasgow University's institute of biodiversity, animal health and comparative medicine, said: "We found that the rhythms of urban birds in the wild differ significantly from their forest counterparts.
"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."
Not only did they get less sleep, they also had more disrupted circadian rhythms, according to Davide Dominoni, another one of the researchers. "The strength of the activity cycle produced by the circadian clock was weaker in urban birds," he writes in an email. "It basically means that it was more difficult to detect a clear pattern of activity/rest in the urban birds. Their activity cycle under constant laboratory conditions was more 'messed up'."
Dominoni added that it's unclear how deep the effects go. "We also need to elucidate whether these changes in the circadian properties of urban birds are a consequence of evolution (change in gene frequency or expression), or simply a side-effect of city life (what we call 'phenotypic plasticity)," he writes.
The study did not undertake to find whether the the longer waking hours have any negative effect on the birds. But the researchers noted that in numerous other studies, human sleep patterns disrupted by nighttime work schedules or other factors have been shown to produce bad health outcomes.
This research opens the question of whether simply living in a city might do the same by altering the natural circadian clock.
From the BBC:
Dr Helm added: "Previous research undertaken by other researchers has suggested strong links in humans between disrupted sleep patterns and an increased incidence of depression and diseases including obesity and some types of cancers.
"Our work shows for the first time that when sharing human habitats, a wild animal species has a different internal clock.
"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. This may help us to better understand the challenges of coping with urban life."
Dominoni says it's unclear whether the advantages of a changed biological clock outweigh potential disadvantages for the birds. "For animals living in cities nothing is really known," he says. "We need to investigate potential costs ... but also benefits of being active at night. For example it is known that male songbirds that sing earlier in the morning are able to increase their reproductive success by attracting cheating females from neighboring territories and copulating with them."