Birds in cities often sing at a higher pitch, perhaps to be better heard against higher levels of background noise. Photograph: Sue Tranter RSPB Images/PA Wire

Foxes loitering around rubbish bins and pigeons roosting in train stations: urban animals are widely regarded as the dregs of the natural world.

However, according to biologist Simon Watt, cities represent some of the worlds hotspots for evolution and behavioural adaptation. Speaking at the Cheltenham science festival, Watt, who is founder of the Ugly Animal Preservation Society, said: The ice caps are melting, the rainforest is shrinking, the one environment that is growing is cities. If were going to look for evolutionary shifts right now in our world, the place to look is cities.

In his talk, Watt cited a host of examples of how the urban environment is prompting new genetic shifts and unexpected behaviours. A proportion of black cap warblers, which used to migrate to Morocco or southern Spain, have shifted their route to Britain where urban heat islands and garden bird feeders allow them to survive at more northerly latitudes than was previously possible.

The ones that come to Britain are starting to get shorter wings better for manoeuvrability, worse for long flights and longer beaks, which are better to get through the wee bars of garden bird feeders, although worse for things like fruits and berries.

In Australia, the mating croak of the male pobblebonk frog has been steadily rising in pitch, an adaptation that means it can still attract females in the presence of the background rumble of motorway traffic.

Pobblebonks never hear their parents, so its an evolutionary shift, said Watt. Outside the urban setting the frogs with the deepest croak tend to be most attractive to females. They still would be the most attractive males if they could be heard, but its become an advantage to have a falsetto, he added. Barry White is out, Justin Bieber is in.

Birds have also changed their vocalisations, although this appears to be acclimatisation rather than evolution. In general we can say that birds in cities have a couple of things in common. They tend to sing at a higher pitch, they tend to use fewer notes and they tend to sing faster, he said. They have their own urban music. This happens across all the species, they sing at different times at night because theyve got street lights. They are not quite sure when its bedtime. It does mean that some of these birds are stressed out.

A weed, called Crepis sancta which looks like a delicate version of the dandelion, is evolving to release higher numbers of heavy seeds and fewer light floaty ones (the plants produce a mixture) because of its concrete-bound existence. If youre in concrete, theres no point in distributing your seeds widely, youre better to just land your seeds in the patch next to you, said Watt.

There is even a species, sometimes known as the London Underground mosquito, which has adapted from a southern mosquito variety to survive in the warm underground spaces of northern cities.

Watt said the types of species that are able to thrive in urban environments tend to be adaptable omnivores, relatively intelligent and scavengers by nature.

In other words theyre rather a lot like us, he said. He added that the changes taking place in the urban environment were sometimes neglected, even by the scientific community. We dont have to go to Borneo to watch evolution in action.

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Cities should be studied as evolutionary hotspots, says biologist - The Guardian