Darwin's finches (also known as the Galápagos finches) are a group of about 15 species of passerine birds that evolved from a single original species. The smallest is the Warbler Finch and the largest is the Vegetarian Finch. The most important differences between species are in the size and shape of their beaks, and the beaks are highly adapted to different food sources.
Natural history museum collections are tremendous repositories of specimens and data of many sorts, including phenotypes, tissue samples, vocal recordings, geographic distributions, parasites, and diet. Photo by Jeremiah Trimble, Department of Ornithology, Museum of Comparative Zoology, Harvard University.