AOU Wednesday: Darwin’s finches still giving up secrets

By Hugh Powell
August 6, 2008
Darwin’s finches, by John Gould, ca. 1845
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8:00 a.m. Dr. Rosemary Grant of Princeton University started the morning off discussing how species appear (the subject of her latest book), using for inspiration her 35-year studies of Darwin’s finches. Those are the drab songbirds Darwin ran across in the Galapagos Islands, notable for their assortment of beaks: a set of tools worthy of an entire garden shed. Grant is a slight, white-haired English woman with a hint of Scotland in her accent, and I couldn’t help but think of Professor McGonagall as I listened.

Grant described Isla Daphne, a puckered traffic cone of an island dotted with cactus and scrub, 500 miles west of Ecuador in the Galapagos. Studying the fortunes of three species of finches, Grant noticed that, very rarely, young finches learned the song of the wrong species. When the bird grew up, it often mated with the wrong species – and surprisingly, their hybrid young survived to breed. Over several generations, Grant noticed that on Isla Daphne, at least, traditionally separate species were beginning to merge back toward one.

This unexpected mixing is possible, Grant said, because it takes in the neighborhood of 30 million years for birds to become genetically incompatible – whereas Darwin’s finches have only been around for about 3 million years. Many birds we call different species are physically separated – they never get the chance to test their genetic compatibility because they live in different places. But differences like beak shapes and feather colors can evolve much more quickly than that.

In one respect, Grant’s findings bring up an age-old (and, some would say, tiresome) conundrum: What is a species anyway? But the really interesting part, she said, is the possibility that hybrids periodically add a burst of new traits into a species’ gene pool, providing a swift kick to the course of evolution. I’ve started to think of it as the labradoodle effect.

10:30 a.m. After Grant’s hourlong meditation, the onslaught of 15-minute talks resumed. For example, we learned that the charming Eastern Bluebird may actually be a jealous landlord that evicts Brown-headed Nuthatches from nestboxes around Charlotte, North Carolina.

12:00 noon. Alaskan King Eiders are considerably more tender hearted. As they migrate along the coast of the Chukchi Sea, in western Alaska, they mingle with eiders from Siberia. When spring comes, the females head for their summer homes, and Russian males are sometimes so lovestruck that they follow them to a new home on a new continent.

Final thoughts: As Grant ended her talk, she elegantly shifted from evolution to conservation, pointing out the success with which Darwin’s finches have survived the sudden shifts in climate continually thrown at them by El Nino and the eastern Pacific Ocean. She quoted Darwin, with a line to remember:

It is not the strongest of the species that survive, nor the most intelligent, but the one most responsive to change.

And with that, it’s off to the afternoon sessions.