#geospiza

Evolution in action detected in Darwin's finches

The most characteristic feature of Darwin's finches is the diversification of beak morphology that has allowed these species to expand their utilization of food resources in the Galápagos archipelago. A team of scientists from Uppsala University and Princeton University has now identified a gene that explains variation in beak size within and among species. The gene contributed to a rapid shift in beak size of the medium ground finch following a severe drought. The study is published in Science.

Darwin's finches are a classical example of an adaptive radiation. Their common ancestor arrived on the Galápagos about two million years ago. During the time that has passed the Darwin's finches have evolved into 18 recognized species differing in body size, beak shape, song and feeding behaviour. Changes in the size and form of the beak have enabled different species to utilize different food resources such us insects, seeds, nectar from cactus flowers as well as blood from seabirds, all driven by Darwinian selection. In a previous study from the same team the ALX1 gene was revealed to control beak shape (pointed or blunt) and now a gene (HMGA2) affecting beak size has been identified.

Absurd Creature of the Week: The Tiny Blood-Slurping Bird That Terrorizes the Galapagos

Ken Petren, an evolutionary ecologist at the University of Cincinnati, landed on Wolf Island in April to study these remarkable vampires, actually a subspecies of the sharp-beaked ground finch, and didn’t even lose his mind and eventually throw his colleagues overboard. “I could say that I was pretty skeptical of the whole vampire finch thing, having heard about it and realizing that there’s not a ton of data on it, mostly just some observations,” he said.

But what he found was far more macabre than the typical recorded accounts of vampire finches pestering the living daylights out of adult boobies. “On this island they really seem to be purposefully going up to a booby chick in the nest,” Petren said, “and they peck at the base of their tail where they have oil glands, and they make it bleed and they drink the blood.”

Even more menacing, they have a habit of gathering in mobs for such endeavors, watching each other intently to learn how to be unimaginably annoying for the rest of their lives. And although Petren saw them swarming dead chicks, he hesitates to conclude that the finches were responsible for the deaths. Life in this hot, dry environment is tough, so mortality rates for seabirds are quite high as it is, and he has no direct observations of finches actively hunting the babies.