The researchers compared the city bird genes with the genes of their relatives in the countryside. The findings, which are published today in Nature Communications, showed that it didn’t matter if the great tits lived in Barcelona, Malmö or Glasgow: in order to handle an environment created by humans, the city birds all evolved in a similar way.

The European research, which was led by Lund University in collaboration with researchers at the University of Glasgow, included a study of birds from Kelvingrove Park together with birds from around the forest in the University of Glasgow’s SCENE (Scottish Centre for Ecology and the Natural Environment) facility, located near Loch Lomond.

The researchers found that different genes linked to important biological functions regulated by serotonin, including aggression and circadian rhythms, were found to have been selected and passed on from generation to generation in the city birds. In rural populations, these behaviours are also important, however, the genes that control them do not confer the same advantage as they do in an urban environment.

Caroline Isaksson, Senior Lecturer at Lund University, led the study together with Dr Pablo Salmón, now a research fellow at the University of Glasgow. She said: “This indicates that these behaviours, and cognition, are very important in order to live in urban environments with a lot of stress in the form of noise pollution, light at night, air pollution and constant proximity to people.”

The study is the largest carried out on how urban environments affect the genome, and thus the genetic material of the animals that live there. In total, 192 great tits were examined among populations in Malmö, Gothenburg, Madrid, Munich, Paris, Barcelona, Glasgow, Lisbon and Milan. For each urban population, the researchers had a control group of great tits living nearby, but in a rural environment. Blood samples have been taken from the birds and analysed genetically.

Dr Pablo Salmón, from the University of Glasgow, said: “It is surprising that cities, which from an evolutionary perspective are a recent phenomenon, are already leaving their footprint in the genome of birds.”

The researchers analysed more than half a million single-nucleotide polymorphisms (SNPs) spread over the entire genome, and found that a handful of genes that had clearly changed in response to the urban environment.

Great tits are common throughout Europe, and it has long been known that they are quite similar genetically. Despite this, researchers have now identified clear genetic differences between great tits in the city and great tits in the countryside.