Birds can evolve so fast that scientists can watch it happen

You can count on your fingers the number of years it takes for a bird species to visibly evolve, biologists are discovering.

Two new studies add to increasing evidence that even large, long-lived animal species can adapt physically and genetically to changes in their environment — and even give rise to new species — faster than we ever thought.

A new paper published today shows endangered birds of prey called snail kites in Florida have grown measurably bigger beaks in the past decade as they consume an invasive snail that's five times bigger than the one they normally ate, and changes can already be seen in their DNA too.

That comes on the heels of a study published last week that showed a new species of Darwin's finch recently arose in the Galapagos over the course of just five years.

"Evolution can operate incredibly fast, in the wild in natural populations," said Robert Fletcher Jr., a biologist at the University of Florida who co-authored the new study on snail kites published today in the journal Nature Ecology & Evolution. "And this really changes the way we view ecology."

Snail kites are birds of prey found through Central and South America, but are endangered in the U.S., where they live only in Florida. Around 2010, there were only around 700 left in Florida. Unlike familiar hawks and eagles that mainly eat rodents, fish and small birds, snail kites prefer to dine on escargot — their favoured prey is the Florida apple snail, which they extract from its shell using their curved beak and long claws.

Then, the invasive island apple snail, native to South America, arrived in Florida. The meaty new snail, a pest that's devastating to crops such as rice, was five times bigger. It invaded a wetland on the edge of the kites' breeding grounds around 2004.

"Nearly all the snail kites moved into this one wetland almost instantaneously," Fletcher recalled in an interview with CBC News.

At first, things didn't go well — the researchers worried as they watched the birds repeatedly fumble and drop the jumbo-sized snails.

Saved by invasive pest?

But after several years, the kite population grew and more chicks survived their first year.

Fletcher wondered if the birds were changing physically from generation to generation to adapt to their new prey.

"Nobody would believe me," he said with a laugh. "They said, 'No, that cannot be. It's too quick.'"

But when his team measured the birds' beaks and bodies as part of other work, they noticed that both were getting bigger, especially the beaks.

"The bills of these birds are now larger than would be expected relative to body mass," they reported in the new study.

That alone isn't necessarily evidence of evolution, which is defined by the change in frequency of certain genes in the population over time, rather than physical characteristics (although physical characteristics may change if they're linked to genes.)

Ready to evolve

But the researchers found that chicks with larger beaks were more likely to survive their first year, suggesting that natural selection should be happening. And they found that the birds were showing more variation in genes linked to bill size than they were before the invasive snail arrived.

That may be because some genes are only triggered by certain environmental conditions. For example, a bird may have the genetic potential to grow a very big beak, but only if it exercises its beak muscles by eating larger prey when it's young. Otherwise, it will have the same beak size as other birds. That type of hidden genetic variation "gives the machinery, if you will, for evolution to proceed more rapidly than what we would have expected," Fletcher said.

But the researchers are still trying to figure out what's allowing the birds to show such big changes in beak size in less than one-and-a-half generations.

"We weren't expecting it," Fletcher said, and that's why they weren't in a position to do the types of analysis necessary to figure that out right away.

Rapid evolution within decades has previously been seen in smaller, seed-eating birds such as Darwin's finches on the Galapagos islands in response to climate fluctuations, and house finches and great tits in response to bird feeders. But biologists weren't sure that could happen with animals like kites that are predators with more than half a decade between generations.

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Now it appears that can happen, and that could be good news for their conservation.

Brand new finch

Meanwhile, those rapidly evolving Darwin finches have demonstrated a new evolutionary trick — producing a new species in just two generations.

Researchers from Princeton University in the U.S. and Uppsala University in Sweden documented the birth (or hatching) of a new finch species they call "Big Bird" on the Galapagos Island of Daphne major in a new paper published last week in Science.

The saga began in 1981 when a young large male cactus finch of the species Geospiza conirostris flew more than 100 kilometres from Espanola island to Daphne Major. Peter and Rosemary Grant, two researchers from Princeton University, noticed his arrival because they had been studying the Galapagos finches for decades.

The foreign bird later mated with a local medium ground finch of the species Geospiza fortis. They produced offspring with such an unusual song that they couldn't attract mates from any of the four local species on Daphne Major, so they mated among themselves. That kind of "reproductive isolation" is one of the very strong criteria that defines a new species, said Sangeet Lamichhaney, a postdoctoral researcher at the Museum of Comparative Zoology at Harvard University. He did the genomic analysis that helped confirm how the new species arose while he was a PhD student at Uppsala University in Sweden.

"This is absolutely exciting," he told CBC News.

He recalled that as a student he thought new species of animals arose over millions of years. His views were updated when his previous studies of the Darwin's finches show that different lineages became separate species between about 1 million and 100,000 years ago.

Now, it seems, a new species of finch can arise on a completely different timescale — in just five years, the amount of time for finches to go through two generations, Lamichhaney said. He added, "I don't think anyone had thought before that in their own life they would see a new species happening in front of their eyes."