1

The Common Cactus Ground Finch vs. the Vegetarian Tree Finch

Hannah Jay and Anaiz Zamudio

El Paso High School

2

Abstract

This paper illustrates the similarities and differences between two of Charles Darwin’s finches: the common cactus ground finch and the vegetarian tree finch. It compares and contrasts information about the two birds, i.e. their eating habits, beak shape, and habitats. This paper also describes how the finches are examples of adaptive radiation, or divergent evolution, and how and why the two species of birds had evolved differently. It also touches on how Charles Darwin used these two species of finches found on the Galápagos Islands to formulate his famous Theory of Evolution.

3

The Common Cactus Ground Finch vs. the Vegetarian Tree Finch

The Galápagos Islands are home to a wide variety of animal and plant life. Included in this array of flora and fauna are thirteen species of finches, more commonly known as Darwin’s finches because of the famous naturalist’s use of these birds in formulating his Theory of Evolution. Two of these species are the common cactus ground finch, or the Geospiza Scandens (Ellert, n.d.) and the vegetarian tree finch, or the Platyspiza Crassirostris. While these two birds live on the same set of islands, they are quite different.

The Cactus Ground Finch

The common cactus ground finch is found on the desert areas of all of the major islands of the Galápagos, with the exception of the island of Floreana. Its diet consists of flowers from the Opuntia cactus, and the pollen from the flowers leaves a yellow dust around the beak of the bird. The finch’s beak, because of its diet, has evolved into a long yet down curved shape. The cactus ground finch also resides in the Opuntia cactus, where it feeds.

In Charles Darwin’s expedition to the Galápagos, he actually thought the finch was a blackbird because the males are primarily all black while the females are a light brown color. The birds are typically tiny, and weigh only about 20 grams. The birds have evolved this way because of their need to blend in with the desert surroundings and, in the males’ case, the cactus’s shadow. Their beaks have curved downward because they need to drink the nectar from the Opuntia’s flowers, like a hummingbird.

4

The Vegetarian Finch

The Vegetarian Finch is beck is quite unique, due to its diet. Its beck is similar to a parrots by being short and thick , it curves down ward. Like most species of Darwin’s Finches beck being yellow and later on changes to a black color during the mating season. The Vegetarian Finch is indigent to the Galápagos Island. They prefer to by in higher elevation.

The Vegetarian Finch’s diet mainly contains plant matter, fruits, seeds and although they may also occasionally eat a few insects. These Fiches have a unique habit on which it strips bark from the twigs of Croton Scowler so that they can eat the sugary substance inside. The setting on which they consume their food is mostly in trees, but the birds may also eat the fallen