Unedited videos reveal the sophisticated tool-using behavior of Hawaiian crows


Enlarge / A Hawaiian crow will carefully choose and shape a stick to snag food. (credit: Ken Bohn / San Diego Zoo Global)

Here’s some news that will justify your corvid love. A new research project in Hawaii, described in a recent issue of Nature, has revealed that crows throughout the world are capable of evolving tool use under the right environmental circumstances. Zoologist Christian Rutz has worked for years with crows on the Pacific island of New Caledonia, who routinely use specially-crafted sticks and serrated leaf edges to retrieve bugs and larvae from hard-to-reach spots in logs. Though Rutz and his colleagues speculated that other crows must use tools, there were no recorded observations of the practice. Until now.

In this unedited clip, a Hawaiian crow or ‘Alalā spontaneously uses a stick to tug a tasty treat from a hard-to-reach spot in a log.

Rutz and a team of researchers worked with a group of 104 ‘Alalā, or Hawaiian crows and discovered that they used sticks in ways that are very similar to New Caledonian crows. Though the two species are not closely related, they have a few traits in common. Both have long, straight beaks and eyes that are very mobile, which the researchers believe make them particularly adept at using their beaks to guide sticks. To grab a tasty grub out of a log, a crow has to find a stick of the right length, smooth it by removing bark or branches, and then thread it into a small opening to root around and yank out the unlucky invertebrate. ‘Alalā and New Caledonian crows also share similar ecosystems: both are island birds, who live in areas with few predators. Unfortunately, human disturbances in the Hawaiian environment have driven ‘Alalā extinct in the wild. Rutz and his team worked with birds who live in two different enclosures on the Big Island, using a special “testing log” full of nooks and crannies, to see how they used tools to get at food.

One question is whether ‘Alalā learn to use tools from their families, or start using tools spontaneously. The latter would suggest that tool use is essentially a heritable behavior, passed down through genetics rather than socialization. To find out, the researchers reared 7 ‘Alalā in an enclosure without adults. Within months, all of them began to use sticks to retrieve food. Though adult ‘Alalā no doubt help their young learn the best ways to prepare and find sticks, it’s clear that this isn’t exclusively a learned behavior. The birds will do it even without any training. Because ‘Alalā and New Caledonian crows are so distantly related, their tool use is a clear example of convergent evolution, where similar traits arise in two unrelated populations.

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