Which group of Galápagos birds did Darwin study that showed beak variation?

The Galápagos bird group Darwin studied for beak variation is known as Darwin’s finches. The name covers about 18 closely related species whose beaks differ in size and shape, adaptations linked to different foods and habitats across the islands.

Darwin encountered these birds during the second voyage of HMS Beagle in 1835. At first, he did not fully appreciate their significance and failed to label every specimen by island. The ornithologist John Gould later identified the Galápagos birds as a distinctive group of related finches. Comparing them helped Darwin recognise how isolated populations could diverge.

The birds became a classic example of adaptive radiation, although Darwin’s finches are not true finches: they belong to the tanager family. Darwin also studied Galápagos mockingbirds, whose island-by-island differences were especially important to his thinking, but the famous beak-variation group is Darwin’s finches.