Cities are creating new species

Researchers in the US found that the wingspan of American cliff swallows, which took up the habit of colonising concrete highway bridges in the 1980s, had decreased by about two millimetres a decade since then. Not much, and perhaps not really worth noticing if their measurements on the roadkill had not shown the exact opposite pattern: by the 2010s, the wings of dead birds by the roadside were about half a centimetre longer than those of live birds still happily flapping along. Also, even though the pressure of traffic had remained the same or even increased, the numbers of dead birds declined by almost 90%.

Across Europe and North Africa, city blackbirds have been found to have shorter, stubbier bills than forest blackbirds, presumably thanks to the easy pickings at bird feeders and other places in the cities where food can be had without pecking, probing or pincering. Whether it’s due to those different beaks is not sure yet, but urban blackbirds sound different too. The urban background noise forces the blackbird songsters to change their pitch and timing.

As researchers in the Netherlands found out after recording almost 3,000 songs, urban blackbird concerts are performed at a higher pitch than forest ones, while a German research team discovered that, as foretold by Paul McCartney, urban blackbirds are singing in the dead of night. In the city centre of Leipzig, they start a full three hours before sunrise, well before the trams and cars start creating a racket. Forest blackbirds open their beaks only at dawn. They also start breeding earlier in the year than their sylvan relatives, as their biological clocks are advanced by more than a month.
https://www.theguardian.com/cities/2018/jul/23/darwin-comes-to-town-how-cities-are-creating-new-species