City life is notoriously stressful, altering hormone levels and taking its toll on the immune system. Now, new research in birds suggests it might accelerate the aging process as well. To investigate how an urban upbringing influences aging, researchers fostered great tit chicks (Parus major) from either city- or country-dwelling parents, with urban or rural foster parents. After 15 days, the team took blood samples to measure the length of each chick’s telomeres—the genetic “cap” at the end of each chromosome that helps protect it from damage. They found that great tit chicks raised in urban environments (right, above) had shorter telomeres, on average. Regardless of their birthplace, city-raised chicks’ telomeres were 11% shorter than those of chicks raised in the countryside, the team reports today in Biology Letters . Telomere length is thought to reflect aging at the cellular level, and their gradual degradation over time may play a role in many age-related problems such as liver dysfunction and cardiovascular disease. The authors suggest that increased stress because of city pollution, which can cause DNA damage, is to blame for the rapid cellular aging seen in great tit chicks. Although it isn’t clear yet how widespread this phenomenon is, shorter telomeres may mean a shorter life expectancy for all city life, including humans.