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On a recent morning, Shultz opened a wooden tray to reveal rows of house finches, a palm-sized bird commonly found in Los Angeles.

For example, Darwin's finches illustrate how such changes can manifest: They have evolved different beak shapes adapted to various food supplies available on the Galápagos Island.

Vampire ground finches will resort to feasting on the blood of other birds if conditions are particularly harsh.

Their numbers, however, have increased significantly in proportion to the backyard bird feeders that support and contribute to their prey base, from hummingbirds to house finches.

Zebra finches, also studied by the researchers, have the same general organization with slightly less sensitivity in some areas than hummingbirds, suggesting that these areas help with highly specialized hummingbird flight dynamics.