Gizmo Bird Beak

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Use the Gizmos to complete the questions below.

EQ: How does environment impact natural selection process?

Observe finch populations and beak shapes during normal years.

 Understand how annual rainfall affects the amount and types of available seeds.

 Explore how finch populations change in times of drought and excess rainfall.

 Identify examples of directional and stabilizing selection.

 Explain how new species of finches could arise.

Scientific Background:

Among the thousands of biological specimens collected by Darwin during the voyage of the HMS Beagle were a group of birds from the Galapagos Islands. The birds were distinguished by a variety of beak shapes and differing lifestyles and diets. Some of the birds are seed eaters and live on the ground, some eat insects and live in trees, and one species actually feeds on the blood of other birds! Yet another species uses cactus spines to pry grubs from trees, a rare example of avian tool use. Darwin didn’t pay much attention to the birds at the time, but he was later surprised to learn that all the birds were closely related finches. Darwin soon understood the implications of this fact. He imagined a small group of finches that were lost at sea, perhaps blown off course by a storm. These finches eventually landed on the desolate Galápagos Islands, an environment completely different from the lush forests of their homeland. Over the years, the finches adapted to take advantage of new food sources. Through the finches, Darwin visualized how the process of evolution and the formation of new species could occur. Today, Darwin’s finches are considered a classic example of an adaptive radiation leading to the formation of new species. In 1973, the husband and wife team of Peter and Rosemary Grant began a remarkably detailed study of the medium ground finch, Geospiza fortis. In four decades of visiting the islands, they and their colleagues have observed the finches in times of normal rainfall, above-average rainfall, and extreme drought. On the island of Daphne Major, only one inch of rain fell in 1977. The Grants discovered that the finches did not breed that year, and few seeds were produced by the plants on the island. The smaller seeds were quickly consumed, leaving behind only the toughest, hardest seeds. The medium ground finch population decreased drastically that year, but finches with the smallest beaks were hit hardest. As a result the average beak depth increased. Two years later came a period of heavy rains. Vines overgrew much of the island and produced massive numbers of small, soft seeds. The finches had multiple clutches of eggs that year and their population increased rapidly. Although medium ground finches with all beak sizes flourished, the finches with the smallest beaks underwent the greatest increase in population. Thus, the average beak depth decreased. These and other discoveries are described in the Pulitzer Prize winning book The Beak of the Finch by Jonathan Weiner.