Hawaiian crows (Corvus hawaiiensis) use tools when foraging for food, finds an international team of scientists and conservationists. These birds, also known as ‘Alalā, rival New Caledonian crows in their proficiency and dexterity with tools. The discovery was published on Wednesday in the journal Nature.
Only a handful of bird species use foraging tools in the wild. The New Caledonian crow (Corvus moneduloides) is a stand-out even amongst this select group, due to its highly sophisticated tool-making and using skills. New Caledonian crows live only on the remote South Pacific island of New Caledonia where they have long impressed and intrigued scientists. The big question was why this species, but apparently no other members of the crow family, used tools.
While working with New Caledonian crows, St. Andrews University biologist Christian Rutz noticed the birds’ unusually straight bills and large, highly mobile eyes. Rutz wondered whether these could be adaptations for holding and handling tools.
“There are over 40 species of crows and ravens in the world, and many of them are poorly studied because they live in remote tropical locations,” says Rutz. “I suspected there could be other, unstudied crow species out there that have the same tool-using skills as the New Caledonian crow, and we could systematically search for them by looking for these unusual facial features.”
When Rutz looked for other crow species with straight bills and large eyes, the species that stood out was the Hawaiian crow.
But the Hawaiian crow is extinct in the wild. In the midst of a precipitous decline in the late 20th century, conservationists caught the remaining wild birds and brought them into captivity for a breed-and-release program.
“I got in touch with the team that looks after these crows in captivity in Hawaii, and I told them I had a hunch their crows may be tool users,” says Rutz. “They said, ‘Yeah, we see that all the time.’”
The scientists and conservationists collaborated to examine the tool-using skills of Hawaiian crows under controlled conditions, testing 104 of the 109 Hawaiian crows alive at the time. They found that 78% of the birds spontaneously used stick tools to probe for food in holes in a wooden log. Nearly all the adult birds used tools, while juveniles learned to use tools over time, even when they were never exposed to adults modeling tool behavior.
“It didn’t look like the kind of tool behavior that sometimes arises in a species in captivity, where the animal does not naturally use tools in the wild,” says Rutz. “Those attempts are often quite clumsy. With the Hawaiian crows, they are so quick and dexterous in how they pick up the tools and how they modify them for use.”
Rutz also points out that if tool use were an artifact of living in captivity, one might expect only a handful of individuals to try the behavior. But tool use appears to be a species-wide capacity in Hawaiian crows.
One more line of evidence suggests that tool use is part of the Hawaiian crow’s natural behavioral repertoire: juvenile crows developed functional tool use without training or the opportunity to observe adults successfully foraging with tools. So, since almost all the birds 1) used tools when they were given the opportunity, 2) were quite skillful with the tools, and 3) acquired tool use behavior with no training, it seems likely that Hawaiian crows once used tools in the wild as part of their normal behavior.
As crow species go, the Hawaiian crow and New Caledonian crow are only distantly related, suggesting that tool use evolved independently in each bird. What the two species have in common is that they evolved on similar remote tropical islands in the Pacific Ocean. New Caledonia and Hawaii both lack woodpeckers (reducing competition for prey embedded in trees) and ferocious bird predators (reducing the risk of predation while foraging). Conditions like these could facilitate foraging tool use in birds.
The first release of captive-bred Hawaiian crows into the wild is scheduled in only a few months’ time. Research like this provides useful information for the species’ conservation.
“The discovery that Hawaiian crows naturally use tools provides an unexpected insight into these birds’ ecological needs that we will use for the forthcoming reintroduction,” says Rutz. “We can look at the New Caledonian crow and try to anticipate and model what these birds will require upon being released; a tool-using species occupies a different ecological niche than a non-tool-using species.
“Hopefully, learning about this interesting research will familiarize people with these birds and encourage people to care about them and support conservation efforts.”