Science in the Triangle

If Charles Darwin returned to the Galapagos Islands today, he would find all but one of the finch species that lived there during his visit in the 1830s. But he would also find birds that look and sound different.

Peter and Rosemary Grant, husband-and-wife evolutionary biologists at Princeton University, have written about a medium ground finch that is heavier, has a broader beak and sings a different song than its closest relative.

The Grants have documented the emergence of this medium ground finch lineage since 1981, when they caught what they believe was an immigrant bird on Daphne Major, a tiny Galapagos island where they’ve measured, weighed and tagged ground finches several months every year since 1973.

The new lineage, which nobody has dared to call a new species yet, has been molded by droughts, above average rainfall and competition for food - factors that also affected other finches living on Daphne Major.

“In the 2000s, the birds are not the same as the ones that were on the island when we started,” Peter Grand told a crowd of more than 200 who had come to his and his wife’s presentation April 11 at the N.C. Museum of Natural Sciences in Raleigh.

That evolution can happen as researchers watch was unexpected. That the Grants documented the making of what might be a new species in 20 years has turned them into legends.Their research has won multiple awards and is featured prominently in biology textbooks and one Pulitzer-Prize-winning book.

The couple’s visit to North Carolina’s Research Triangle was the result of a collaboration of the museum, N.C. State University and the National Evolutionary Synthesis Center.

Thirteen species of ground finches live on the Galapagos archipelago, a cluster of more than a dozen islands located in the Pacific Ocean about 600 miles west of Equador. They are plain birds with brown, gray or black plumage that have been famous since they helped Darwin develop the theory of evolution.

All descend from one species that lived on the South American mainland.

The smallest finch species on the Galapagos Islands weighs about one-fourth of the largest species and each species has developed a specific beak to eat a special diet.

The Warbler finch has a slender beak to probe for insects. Ground finches have broad beaks to crush seeds of various sizes. Cactus finches have long, curved beaks to probe flowers for nectar. The large tree finch has a powerful, curved beak to strip bark and extract insects and termites.

The diet has a lot to do with where a species lives. The medium tree finch, for example, can only be found on Floreana Island. The common cactus finch lives on all but the five Galapagos Islands that are inhabited by the large cactus finch.

Daphne Major is home to four species, the Grants reported. The couple caught small, medium and large ground finches and cactus finches, including some that had immigrated from neighboring islands.

The males of each species sing a different song, which male and female birds learn as nestlings listening to their fathers. Males and females of a species recognize each other by that song. Interbreeding can occur, Rosemary Grant said, for example, when the fatherly lesson gets garbled because the nest is close to the nest of another species in the same cactus bush.

In 1981, the Grants caught a medium ground finch immigrant whose plumage was particularly glossy and black. The male bird was about 20 percent bigger than the biggest medium ground finch captured on Daphne Major and had a wider beak. It also sang an unusual song and a blood test determined that it carried cactus finch genes.

The immigrant hybrid male mated with a female hybrid that also carried genes of both species. Three generations of offspring - finches live up to 16 years - bred with local medium ground finches and other hybrids.

Then, all but two of the birds in the lineage died during a severe drought in 2003 and 2004. The remaining two birds, a sister and a brother, mated and their offspring has mated, but only with each other.

This has led to two distinct groups of medium ground finches on Daphne Major that do not mix, the Grants reported. They differ in weight, beak shape and song and breed in two different areas on the island.

 

 

 

 

 

 

 

 

(More in the Grants’ inaugural article in the 2009 Proceedings of the National Academy of Sciences.)