Overview
- A peer‑reviewed study published Thursday found that wrens from four Scottish islands are genetically distinct from mainland British wrens, with the strongest divergence on Shetland and St Kilda.
- Wrens on St Kilda weigh about 13–16 grams compared with 7–10 grams on the mainland, making the largest St Kilda birds more than twice the mass of the smallest mainland individuals.
- Shetland birds average roughly 2.9 grams heavier than mainland wrens and Outer Hebrides birds are about 1 gram heavier, while Fair Isle shows little size change.
- Whole‑genome data show limited recent interbreeding and that similar large‑body outcomes on Shetland and St Kilda arose via largely different genomic changes, consistent with parallel evolution.
- Researchers collected body measurements, song recordings and genomes to reveal matching shifts in song, plumage and proportions, and they say the populations offer a natural model to study how island conditions drive evolutionary change without yet prompting formal taxonomic reclassification.