City blackbirds live longer but have worse health

Would you rather live longer and be unhealthy, or have a shorter life, but better health? Luckily that’s a conundrum we as humans don’t necessarily have the ability to determine. But if you’re a blackbird living in European cities – and you have the ability to read a new study published in Biology Letters – that may be a choice you can make, whether you know it or not.

Research led by University of Groningen biologists has determined that blackbirds living in five European cities live longer than those living in the forests in proximity to those cities. However, this comes at a cost. Their research also found that the city birds have a significantly poorer health status than the rural birds.

The researchers travelled to Granada, Seville, Madrid, Dijon, and Turku to obtain blood samples from the blackbirds living in these cities, as well as adjacent rural areas. They then compared the length of telomeres – the repetitive sequences of DNA that are the protective end caps of chromosomes – between city birds and rural birds. The length of telomeres is an unambiguous marker of health, as they protect DNA from deterioration over time. Through the natural processes of aging, telomeres become shorter, but stress can accelerate this shortening.

Age of each bird was also assessed, as scientists are able to distinguish older birds from yearlings through observing the moulting pattern. This allowed them to estimate the proportion of older birds in the populations. Their measurements found that the telomeres of city yearlings were substantially shorter than those of rural yearlings, and this difference was even more pronounced in older birds.

This means that city birds were showing signs of premature aging, signifying that they weren’t as healthy as rural blackbirds. However, the proportion of older birds was higher in the cities. “This means that mortality is lower in the cities, so the advantages of city life compensate for the negative health effects,” explains Juan Diego Ibáñez-Álamo, a University of Groningen postdoc researcher and lead author of the study.

The reasons behind why the city birds seem to live longer, but are less healthy, is unknown. But it could potentially be because there is less predation and more food in cities. The researchers explain that the reason could also be that birds with short telomeres ended up living in the cities, and simply created a population characterized by short telomeres. But more research must be done before the implications of this study are fully known.

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By Connor Ertz, Earth.com Staff Writer

Image Credit: Richard Ubels / University of Groningen