Rainfall and Bird Beaks

When he visited the Galapagos Islands in 1835, Charles Darwin did not think much of the dull-colored finches he collected from the Islands. It was only after he returned to England and the ornithologist John Gould identified them as 12 different species that Darwin started to realize their significance. “Darwin’s finches” eventually became one of the key inspirations behind his evolutionary theory.

More than 130 years after Darwin’s visit, Peter and Rosemary Grant began to study Darwin’s finches, spending six months of every year in the Galapagos. Since 1973, the Grants have documented evolution in real time as the size of finch beaks vary in response to precipitation and available food types.

Students can explore these relationships in the Rainfall and Bird Beaks Gizmo. In the Gizmo, students observe and explain the changes in average beak size due to the amount of precipitation. They can then infer how precipitation patterns have affected the food supply on the island.