March 21 (UPI) -- Though blackbirds live longer in the city, urban life takes a toll on their health, new research shows.
When scientists analyzed blackbirds' telomeres, repetitive DNA sequences on each end of a chromosome, they found evidence of significant stress among city-dwellers.
Telomeres act as a protective barrier against chromosomal damage. Over time, they naturally become shorter, but physiological stresses can accelerate the shortening process.
Researchers chose to study blackbirds because they're ubiquitous in cities throughout Europe.
"But they also live in their original forest areas, which makes them ideal candidates for a study of the effect of city life on health," Juan Diego Ibáñez-Álamo, a postdoctoral researcher at the University of Groningen in the Netherlands, said in a news release.
Scientists used nets to capture blackbirds in five different cities and collected blood samples. They also captured birds and collected samples in five corresponding rural locations, each roughly 20 miles outside the city.
The samples were sent back to the lab in the Netherlands for analysis. Scientists found urban blackbirds hosted consistently shorter telomeres than similar aged peers living in the country. The discrepancy was most pronounced among older birds.
However, researchers found a greater proportion of older birds living among urban populations.
"This means that mortality is lower in the cities, so the advantages of city life compensate for the negative health effects," Ibáñez-Álamo said.
Toxins and contaminants, as well as noise and light pollution, may explain the negative health impacts of city life. But the city is also home to fewer natural predators and plenty of food.
Previous research has shown life in the city boosts the intelligence of birds. The latest findings, published this week in the journal Biology Letters, suggest all the advantages of the city come at a cost.
Researchers say more research must be done to determine exactly why and how city birds suffer poorer health than their rural relatives.
"This could be present at birth or develop in the first year, as cities are an unhealthy environment," said biology professor Simon Verhulst. "And it could even be that birds with short telomeres end up in cities and thereby create a population with shorter telomeres."