Adaptation to ancient climate change on St Kilda

Am reading the story of St Kilda by Charles Maclean. Only on the first chapter at the mo where he is talking about the geological and climatological history. Fascinating to read that "some time before the last Ice Age, when the climate was milder and the island lightly forested {with alder, hazel, birch, Scots pine, elm and oak; heaviest tree pollen counts found at heights of 1000ft and more. No trees grow there now}, wrens first migrated to Hirta. As the climate began to deteriorate and the environment to change, the wrens had to adapt to survive. Trees gradually ceased to grow on the island and the wrens had to learn to perch on the rocks and cliffs instead, often in high winds.....They developed larger and stronger feet, longer tougher beaks and generally grew bigger than the mainland birds. Their colouring became drabber though more varied, and their song perculiarly sweet and soft. They now constitute a highly differentiated sub-species known as Troglodytes hirtensis – the St Kilda wren."

I love wrens and I like this story