Songbirds’ evolution linked to geology

Hawaiian honeycreepers, one of the most endangered bird families in the world, likely evolved from Asian rose finches and underwent a huge burst of diversity more than 4 million years ago, scientists using sophisticated DNA analysis have found.

Over the eons, the birds took advantage of the successive development of the four main Hawaiian Islands and found new ecological niches along the way, the scientists report.

Ultimately, they evolved into 55 distinct species, of which 18 remain.

"Some eat seeds, some eat fruit, some eat snails, some eat nectar," said researcher Heather Lerner, an assistant professor of biology at Earlham College in Richmond, Ind. "Some have the bills of parrots, others of warblers, while some are finchlike and others have straight, thin bills. So the question that we started with was, How did this incredible diversity evolve over time?"

The branches of the evolutionary tree are described in a paper set for publication Nov. 10 in the journal Current Biology.

Honeycreepers that remain alive include the apapane, poouli, iiwi and the Oahu and Kauai amakihi. Six of the surviving species are considered critically endangered by the International Union for Conservation of Nature. Four are considered endangered and five are vulnerable.

Using DNA analysis, Lerner and colleagues looked at the evolution of the brightly colored songbirds after the formation of Kauai and Niihau, once a single island.

They found that the largest burst of evolution, called a radiation, happened between 2.3 million and 4 million years ago — after the development of Kauai-Niihau and Oahu but before the development of Maui Nui, a massive island that encompassed modern-day Molokai, Lanai and Kahoolawe.

When honeycreepers from Kauai-Niihau reached Oahu, they encountered a new environment that required them to adapt, said Lerner, who conducted the study as a postdoctoral researcher at the Center for Conservation and Evolutionary Genetics, part of the Smithsonian Institution.

Of 10 distinct groups of species, six formed on Kauai and Oahu, the scientists said.

"It was fascinating to be able to tie a biological system to geological formation and allowed us to become the first to offer a full picture of these birds’ adaptive history," said Helen James, a research zoologist at the Smithsonian’s National Museum of Natural History and a co-author of the paper.