Researchers examined wrens on Shetland, Fair Isle, the Outer Hebrides, and St Kilda, taking body measurements, song recordings, and sequencing their genomes to look for genetic differences compared with mainland birds.
Fair Isle was the only population that was not significantly different in size from the mainland British wren.
DNA studies showed that each island population was genetically distinct, with Shetland and St Kildan wrens found to have the biggest genetic differences to mainland populations.
The Scottish wrens were also found to have a more languid singing style, with songs that included “buzzes”, unlike birds on the mainland. Songs from St Kildan wrens were found to have a lower bandwidth and were of shorter duration.
Shetland birds had longer and deeper bills, while St Kildan birds had wider bills, and longer tails and wings.