Which group of birds did Darwin study to understand evolution?

The group of birds Darwin studied in connection with evolution was Darwin's finches, a group of related birds from the Galápagos Islands. Their varied beaks later became a classic example of adaptive radiation.

During the voyage of HMS Beagle, Darwin collected Galápagos specimens, although he did not initially recognize the finches' importance and was not an expert ornithologist. The ornithologist John Gould later identified the specimens as a distinctive group of closely related finches. Differences in beak size and shape were associated with different diets and habitats across the islands, helping Darwin think about how populations could diverge.

Darwin also studied Galápagos mockingbirds and noted that tortoises differed between islands. These observations contributed to his developing ideas about geographic variation and the stability of species. The finches were therefore part of a wider body of evidence, not the only animals behind his theory.

Darwin's finches are not technically true finches; modern classifications place them in the tanager family. About 18 species are commonly recognized, and modern research—including long-term studies by Peter and Rosemary Grant—has documented natural selection changing beak traits in response to environmental conditions.