Nature & Environment

Massive Scottish wrens demonstrate island gigantism in action

By T.K. Randall
May 29, 2026

Image: Eurasian Wren
Credit: Koshy Koshy / CC BY 2.0 (adapted) When a small animal species becomes isolated on an island, it can sometimes undergo a phenomenon known as island gigantism, gradually evolving to a much larger size over time.

This was observed recently by scientists from the University of Birmingham who investigated wrens - small birds found on Shetland, Fair Isle, the Outer Hebrides and St Kilda in Scotland.

Each island had its own unique subspecies of wren, evolving independently, with several showing clear signs of island gigantism - some growing to nearly twice the size of their mainland counterparts.

"We found that all four Scottish wren subspecies are genetically distinct from the wrens of mainland Britain, with the wrens of Shetland and St Kilda being especially distinct in both appearance and song," said study lead author Dr. Michal Jezierski."Their genetic distinctiveness is so high that it is likely they are on their way to becoming new species."

One of the most famous examples of island gigantism can be found on the Galapagos Islands where some of the native tortoise species have grown to enormous sizes.

Similar examples of large island species can be found all across the world.

It is thought that the lack of predators and reduced competition may be major contributing factors.

Source: Phys.org

Tags: Scotland, Birds