City birds change their tune

85951796_d88118ed0f_o.jpgIn Current Biology, ecologists Hans Slabbekoorn and Ardie den Boer-Visser, of Leiden University in the Netherlands, describe a behavioural adaptation of male great tits to life in the big city.

The Dutch team recorded the songs of great tits (Parus major) from 10 large European cities, including Amsterdam, London, Paris and Prague, and the forested areas surrounding them. A total of 213 songs from urban birds, and 252 rural birds, were recorded and analyzed.

Confirming earlier findings by the same researchers, the current study shows that great tits in urban areas sing faster, and with a higher minimum frequency, than birds in rural areas. This adaptation has arisen to prevent masking of the birds’ songs by human-generated noise.

The vocalizations produced by songbirds are critical for their breeding. Male great tits, like other song birds, produce song to attract a mate, and to delineate their territory. In urban areas, there is an abundance of low frequency ambient noise. This noise is anthropogenic – produced by humans – and includes motor vehicles, planes and machinery. There is, therefore, selective pressure on great tits to adapt to urbanization. Birds that are unable to modify their communication signals to avoid auditory masking in urban environments are likely to have less breeding opportunities, which could lead to a decline in the density and diversity of bird species in big cities.

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