"These birds don't have more kids, they just have the right kids in the right order," said Badyaev.
By exerting control over the sex of the eggs and their hatching order Montana and Alabama finches increase the number of surviving offspring by between 10 and 20 percent more than if the eggs were laid in a random order, according to the research.
The study is published in the January 11 issue of the journal Science.
What is remarkable about this study, say scientists, is that two different populations of finches have acquired such different physical characteristics in such a short period of timebetween 15 and 30 years.
Badyaev believes it is this adaptability that has enabled the finches to spread rapidly throughout the United States.
Early in the 20th century finches were found only in California and the deserts of the Southwest. The birds were brought to the eastern United States and sold as "Hollywood Finches" in pet stores in New York. In 1939 a law forbidding the sale of these birds led pet store owners to release the birds in Central Park to avoid being fined.
By 1985 the New York finches had established populations in Alabama. Finches from Arizona gradually expanded their range, establishing colonies in Montana between 30 and 40 years ago.
Curiously it was the finch populations on the Galapagos Islands that focused Charles Darwin's studies of evolution. He noted that each of the 13 species of finch had a characteristic beak shape that was tailored to a specific habitat and food source.
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