Researchers studying British wrens in remote Scottish island populations report signs that some birds are evolving separately from mainland counterparts. The work examines four isolated populations, including birds from Shetland and St Kilda, and finds that island wrens can become substantially larger than mainland wrens. Scientists report that the biggest St Kilda wrens weigh more than twice as much as the smallest mainland birds. The study also finds evidence that populations on different islands are not only changing in size, but are developing distinct characteristics over time. According to the accounts, this includes differences that may involve song, appearance, and genetic variation, consistent with independent evolutionary trajectories. The researchers frame the findings within the concept of “island syndromes,” where isolated environments can drive parallel kinds of evolutionary change. A paper published in the journal Evolutionary Journal of the Linnean Society, led by the University of Birmingham, highlights particularly strong evidence of “island gigantism” in two of the studied island populations. The researchers say these trends could eventually lead to new species forming, although they do not state that species status has already been reached.