Urban birds may age fast, die young

Urban life has its ups and downs, for birds no less than for people. On the one hand, birds in the city often have easy access to abundant food sources thanks to humans, but on the other they have to contend with stresses like air pollution, traffic noise, and artificial light.

Scientists also know that early life experiences can affect animals’ health and longevity. But no one had looked at the physiological effects on young birds of growing up in a city.

In a new study, scientists from Lund University in Sweden tackled this question by cross-fostering great tit (Parus major) nestlings. They transferred two-day old birds that had hatched within the city limits of Malmö to nests in the surrounding countryside. They also transferred rural nestlings to urban nests.

Then, when the nestlings were 15 days old, they collected blood samples and measured the length of the telomeres in the birds’ red blood cells. Telomeres are caps of DNA at the ends of chromosomes that get shorter as cells age. Within an animal species, individuals with longer telomeres have longer life spans.

Being raised in an urban environment shortens a young bird’s telomeres by over 10%, the researchers report in the journal Biology Letters. Urban-born nestlings reared in a rural habitat had telomeres 11% longer than their siblings that stayed in the city, and rural-born nestlings reared in an urban habitat had telomeres 10.4% shorter than their siblings that stayed in the countryside.

The researchers expected this general result, but were surprised that the pattern was so apparent in such young birds and after so little time in the city.

The finding that birds reared in a city show accelerated aging of their body cells, even while they are still young, suggests that great tits that grow up in the city may have shorter lifespans than rural members of the species.

The mechanisms behind this telomere shortening are not yet clear, but the researchers suspect that pollution and lower-quality food in urban environments play a role. Scientists know that in general, urban birds have higher stress hormone levels and also more oxidative stress; these two factors are known to shorten telomeres.

In the study, the urban-reared nestlings also looked to be in poorer, sicklier condition overall.

“The impact that urbanization has on wildlife must be studied much more, or we won’t be able to understand the threats that birds are exposed to in urban environments, and won’t be able to do anything about them,” says Pablo Salmón, an evolutionary ecologist at Lund University and the study’s first author. “Our results also raise questions concerning the aging of other animals affected by urbanization, and humans for that matter,” he says. – Sarah DeWeerdt | 28 June 2016

Source: Salmón P. et al. “Urban environment shortens telomere length in nestling great tits, Parus major.” Biology Letters DOI: 10.1098/rsbl.2016.0155

Header image: ©Frans Persoon