13 Darwin's Finches-Mid

Darwin's Finches FOCUS Question What can small differences in finch species teach us about adaptations?

Setting Sail In 1831, a ship called the Beagle sailed from England to South America. Some people on board made maps of the continent's coastlines. But a naturalist named Charles Darwin spent his time taking notes about the plants and animals he saw. He visited the Galapagos Islands during the trip. After the journey, he published his notes as a book called The Voyage of the Beagle. Years later, the ideas from his first book led Darwin to write a book called The Origin of Species. This book stated that species evolve—they change over time by passing down certain traits to offspring.

A Living Laboratory The Galapagos Islands, are a group of islands or an archipelago (ar-kih-PEH-luh-go). There are eighteen main islands. and three small islands The islands are 965 kilometers (600 mi.) off the coast of South America. The great distance from the mainland has caused island isolation. The habitats on the islands are different from the habitats on the mainland. When new species arrive on an island, they must find new food sources. They may face unknown predators. As a result, plants and animals can change quickly on isolated islands. For this reason, the Galapagos Islands are a great place to study evolution—how living organisms change over time.

A Bunch of Beaks Among the unique animals on the Galapagos Islands are finches, a type of bird. Fourteen finch species are found only on these islands. Seven of the species live in trees and mainly eat insects. One species lives in trees and eats seeds. Three live in cactuses and eat seeds or nectar. The final three species live on the ground and mainly eat seeds. The beaks of these finches are different sizes and shapes to match their food sources. These birds are often called "Darwin's Finches" because Darwin studied them. He used the ideas he developed from studying these birds to help explain his theory of evolution.

The First Finch How did all those different finches get on the Galapagos Islands? They actually started off as just one species! A few million years ago, a single type of finch reached one of the islands. That finch species is called the ancestral (an-SES-truhl) finch. It lived on the ground and ate seeds. Ancestral finches quickly spread to all the other Galapagos Islands. On each new island, the birds had to compete for different types of food. Those finches whose beak shape and size helped them find and eat food were able to survive and reproduce. This process is called natural selection. Over millions of years, the ancestral finch species became fourteen different species of finch.

Seeking Seeds Many of the islands' finch species mainly eat seeds. But seeds come in different sizes and shapes, and they're found in different places. The small ground finch has a small beak suited to eating tiny seeds. It forages on the ground for the seeds of plants such as the Galapagos carpetweed. A different finch eats larger and harder seeds. The large ground finch has an enormous beak. Snapping open the woody seeds of plants, like the puncture vine, is a cinch for this finch! A third bird, the cactus finch, eats seeds from cactus fruit. It uses its longer, more pointed beak to carefully pull seeds out of the fruit.