Weatherwatch: Tawny owls get tawnier

Climate change is altering the natural world, from earlier springtimes to changes in bird migrations. But one of the strangest effects found so far is an owl that is evolving from a grey to brown colour.

The tawny owl is a stocky owl often found in woodlands across Europe, calling out "kew-wick" and "hoo, ho, ho", or as Shakespeare described in Love's Labour Lost: "Then nightly sings the staring owl, Tu-whit; Tu-who, a merry note."

The owl comes in two different feather colours, reddish-brown or pale grey. The brown birds tend to be more common in the warmer parts of Europe and the grey ones more often found in colder climates.

In Finland, the grey birds tend to dominate, but over the past 50 years records show a steady increase in the numbers of brown birds, and this matches milder winters with less snow, according to a study in the journal Nature Communications. It's thought that the grey-coloured owls are better camouflaged in snow, whilst the brown birds stand out against snow and make easy prey for predators – but they blend into the background when there is no snow around. And as winters have grown milder, so more brown owls have survived and passed on their brown-colour gene, resulting in more brown offspring – a case of evolution in response to rapid climate change.

As snow is expected to become less common throughout Europe this century with rising temperatures, so the numbers of brown owls are expected to increase.