Six consecutive droughts is all it takes for a new species of finch to emerge in the Galapagos islands, scientists have said.

The Galapagos is a province in Ecuador well known for the diversity of finches.

These birds are collectively known as Darwin’s finches because they helped British naturalist Charles Darwin uncover the process of evolution by natural selection.

Researchers have found that drought events can reshape the finch beak and make it bigger and, consequently, dramatically change how their songs sound across generations.

The team discovered older birds would not be able to recognise the calls of younger generations if their beaks evolved as a result of back-to-back drought events, thus making mating difficult between the same species.

The researchers said their findings, published in the journal Science, show that physical changes in birds brought on by extreme events “provide a pathway” for a new finch species to form.

Jeffrey Podos, professor of biology at University of Massachusetts Amherst in the US and the paper’s senior author, said: “I started working with these birds 25 years ago.

“In my very first publication on the finches, back in 2001, I showed that changes in the beaks of Darwin’s finches leads to changes in the songs they sing, and I speculated that, because Darwin’s finches use songs to attract mates, then song changes related to beak evolution could perhaps catalyse ecological speciation (process by which new species arise due to adaptations to different environments).”

In 2017, British evolutionary biologists Rosemary and Peter Grant reported they had witnessed a new finch species evolve in real time in Daphne Major, a small island in the Galapagos, and the process took only took two generations.

It was the first example of speciation that scientists observed directly in the field.

The Darwin finches, a group of about 18 species of passerine birds, are well known for their wide diversity in beak form and function.

But scientists wanted to know whether changes in climate or availability of resources such as food or water can drive the emergence of a new species.

The team digitally created the mating songs of finches based on what they would sound like if their beaks grew bigger after one, three or six back-to-back drought events.

Prof Podos said: “Essentially, we engineered the calls of future finches.”

The researchers found birds with bigger and thicker beaks – evolved to powerfully crush hard seeds during times of drought – sang more slowly.

When the simulated songs of “future finches” were played back to the current ones, the researchers found the birds did not respond to the calls.

Katie Schroeder, the paper’s co-author who participated in this research during her doctoral training under Prof Podos, said: “We found that there were no changes in the finches’ responses to our modified calls even when the simulated songs had changed by the equivalent of three drought events.

“But by six drought events, the had changed so much that the finches barely responded at all.”

The researchers said that because of the links between beaks and song, an entirely new species of Darwin’s finches could evolve in response to six major Galapagos droughts.