The Galápagos experiences a strongly seasonal environment. Finches breed when the rains arrive, typically in January or February. In some years there is no rain and no breeding. This program illustrates the various ways that environmental fluctuations dictate the activities of finches on Daphne. It follows the stages of the breeding cycle, from pair formation and nest building a few days after the first heavy rainfall to fledging about a month later. Breeding ceases when no more rain falls, insects become scarce, and finches then switch to a diet predominately of seeds. As food supply declines the diets of different species diverge and finch mortality increases. Towards the end of the year the shortage of food is ameliorated by the flowering of Prickly Pear cactus. The program concludes by illustrating natural selection in years of drought. In some years Medium Ground Finches with large beaks have an advantage over those with small beaks because they can crack open the scarce large and hard seeds: they have much higher survival. In other years finches with large beaks are out-competed by a larger species, the Large Ground finch, and then those with small beaks survive best. Since beak size is heritable, beak size evolves as a result of natural selection.

Streaming video file encoded with permission for digital streaming by Infobase on September 11, 2015.

Finch Evolution Study --(2:46) -- Finch Mating Songs -- (2:11) -- Insect Food Sources -- (2:58) -- Seed Food Sources -- (2:55) -- Diverging Diets -- (3:01) -- Flower Food Source -- (3:40) -- Commensalism -- (1:54) -- Beak Shape Evolution -- (1:22) -- Competition and Beak Size Evolution -- (3:38) -- Credits: How Finches Feed and Breed: Darwin's Finches in Galápagos -- (0:33).