Why do we have so many types of wren?

BBC Wildlife contributor Mike Toms answers your wild question.

Wren, Troglodytes troglodytes, single bird singing on branch, Warwickshire, April 2012

Six subspecies of wren are known from Britain and Ireland. Five are resident endemics not found elsewhere, and one occurs here as a migrant.

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Shetland (zetlandicus), Fair Isle (fridariensis), the Outer Hebrides (hebridensis) and St Kilda (hirtensis) have their own ‘island’ subspecies, while Ireland, Wales, mainland Scotland and most of England have the ‘British’ wren (indigenus).

In the south-east of England indigenus intergrades with troglodytes, the subspecies found across the rest of Europe. That such a widespread bird should have so many subspecies within our region underlines the sedentary habits of our island forms, which also differ in size, colour and vocalisations.

The differentiation of these island races must have been rapid, because their islands would have been uninhabitable during the last Ice Age.

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Recent research has revealed that mainland wrens are adapted to local climatic conditions, with the larger-bodied individuals found in the north better able to survive extended periods of cold winter weather than their southern counterparts, something else that may have helped these subspecies to form.