You might have taken these extremely intelligent birds as a natural part of the environment, but there has been a doubt as to whether you can see them again, because they have actually become rare.

The Hawaiian crow became almost extinct in the wild. It has now been discovered to be so intelligent that it joins another corvid, the New Caledonian crow, in this "exclusive evolutionary niche".

It was Dr. Christian Rutz from St Andrews University who has given it the rare distinction of being an undiscovered tool user that faces a number of "eureka moments".

"I've been studying New Caledonian crows for over 10 years now," Dr. Rutz said. "There are more than 40 species of crows and ravens around the world and many of them are poorly studied. So I wondered if there were hitherto undiscovered tool users among them."

The New Caledonian crows tend to show distinctive physical features, with "straight bills and forward-facing eyes", which could be seen as tool-using adaptations.

While looking for other species that shared the features, Dr. Rutz discovered that the "Hawaiian crow was the perfect candidate for further investigation".

It had been almost extinct and was rescued by the skin of its teeth.

During the 'save the crow' program, Dr. Rutz worked with his team at San Diego Zoo Global, capturing some wild crows for a breeding programme. In the process they also tested it.

"We effectively tested the entire species," Dr. Rutz said. "At the time, there were 109 crows in captivity - we tested all of them, presenting them with a foraging task."

There are only 130 birds in captivity and none in the wild. 

Zoo president Douglas Myers said: "The discovery that 'alalā naturally use tools is of great significance," he said, "especially at this critical stage of our recovery efforts, as it provides completely unexpected insights into the species' ecological needs."

The team gave the crows logs with holes and bait just out of their reach.

"They were able to pick up sticks from the aviary," said Dr. Rutz, "and of all the birds we tested, 93% used [the sticks as] tools. This suggests this is a species-wide skill.

"They were incredibly dextrous in the way that they handled the sticks, shortened them when they were too long, and discarded them if they were not happy with them."

"By learning about this species' natural tool-using skills, we have a better understanding of their ecological needs," Rutz told Popular Science.This is important because San Diego Zoo Global, who manages these birds, plans to start reintroducing them into the wild. "If everything goes according to plan," said Rutz, "it should be later this year."

Both New Caledonian and Hawaiian crows evolved in far-away islands, so researchers are convinced that something in those islands is driving the evolutionary behaviour of the birds.

Dr. Rutz and his team published their findings in the journal Nature.

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