Adaptive Radiation: The Beaks of Darwin's Finches

On the Galapagos Islands there are thirteen species of finches. When Charles Darwin visited the Galapagos, he noticed that each island was home to a specific species of finch. The diverse species differed in the shapes of their beaks. The beak of each species was adapted to the food sources on their particular island. All the finches are believed to have evolved from a single species that inhabited the mainland of South America. The evolution of one species to fill many different niches is called adaptive radiation. Darwin's finches are a perfect example of this concept. In this activity you will use four different tools to represent the beaks of four species of finches living on one Galapagos island. On this island worms are the main source of food. You will decide which finch has the best beak adaptation for gathering worms.

Materials

Large cup of yarn ''worms'' ; Plastic fork; Plastic spoon; Tweezers; Plastic knife; Clock or watch with second hand

Cut pieces of year into three-inch lengths.  Place about fifty pieces of yarn in a cup.  This cup of yarn will represent bird food.

Activity

1. Spread the yarn worms on a table, which represents one of the Galapagos Islands.
2. You will play the roles of four different species of finches feeding on the worms. Each finch species has a differently shaped beak. The different beak shapes are: fork-shaped, spoon-shaped, tweezer-shaped, and knife-shaped.
3. You will have twenty seconds to pick up worms with the fork, which represents a fork-shaped beak. When your teacher says ''Go,'' begin picking up yarn worms with the fork and placing them in a cup. Cease collecting worms when your teacher says ''Stop.''
4. Count and record the number of worms you picked up. Return the yarn worms to the cup.
5. Repeat this process for each of the other three tools: spoon, tweezers, and plastic knife.

Follow-Up Questions

1. Which of the tools picked up the most worms? What was it about that particular ''beak'' that allowed the finch to gather the most worms?
2. What do you think might happen to the other three types of finches over time if worms were the only possible food source?

Answers

1. Answers may vary, but most students will collect more worms with the tweezers. The tweezer-beak allows the finch to grasp the worm on both sides of the body when lifting it.
2. Answers will vary, but should note that it is possible they might not survive unless they leave the island and go elsewhere in search of food.

Extension

Gather some actual birdseed and determine which beak adaptation would be the most effective in gathering this type of food.