( Royal Society B.) How much of all this has become genetic, heritable and part of evolution?
Some birds, for example, time the birth of their young to match a peak supply of caterpillars feeding on young oak leaves.As warmer and earlier springs encourage earlier budburst, a mismatch of fledglings and peak caterpillars can leave young birds hungry.In a deforested Ireland they spread island-wide and the Dublin ornithologist John Watters knew them well in “the vicinity of gardens, shrubberies, low brushwood, and indeed any locality affording good cover and secure shelter”. American researchers hand-raised urban and forest-living European blackbirds and found that city-born blackbirds have a lower corticosterone stress response than their woodland cousins.The reduced stress response is , they suggest, “presumably necessary for all animals that thrive in ecosystems exposed to frequent anthropogenic disturbances”. But do they sing not only in dead of night but in different voices from those in rural settings?
A study in Spain recorded the songs of 27 blackbirds along a gradient of increasing anthropogenic noise.Instead, the album comes closer to Rihanna’s social media persona: full of (relatively) unfiltered DGAF attitude, with a number of eclectic inspirations.For better and for worse, the songs are more than ever driven by her personality, rather than the other way around.More than half the world’s people now live in concrete settlements.They have created a new world for nature as well – warmer, denser, noisier, more light-filled and polluted than the natural ecosystems beyond the suburbs.The birds did, indeed, change their vocal frequencies along the road, the better to be heard. Another study, comparing blackbird song in the city centre of Vienna and in the Vienna Woods, found that forest birds sang at lower frequencies, with longer intervals between less shrill songs. Why urban blackbirds sometimes sing at night has been explored in experiments.