The other tool-wielding species, the New Caledonian crow found in the South Pacific, is famous for turning sticks into sharp pokers to probe for larvae hidden in trees.
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For the study, the researchers tested 104 of the 109 Hawaiian crows that are alive during their research.
Because the Hawaiian crows are extinct in the wild, and just over 100 individuals live in captivity at the San Diego Zoo Global, the scientists were able to test nearly all the living individuals, save a handful that were excluded for health reasons. “Most studies in our field investigate just a handful of subjects, so it is truly mindboggling to see an entire species tested”, comments Professor Thomas Bugnyar, a corvid expert at the University of Vienna, Austria, who was not involved in the study.
Furthermore, more than two-thirds of the birds modified or manufactured their tools.
Lead researcher Dr Christian Rutz, from the University of St Andrews, said: “Current evidence strongly suggests that tool use is part of the species’ natural behavioural repertoire, rather than being a quirk that arose in captivity”.
The team gave the crows logs with holes and bait just out of their reach.
All this was set up under an opaque sheet, so the birds wouldn’t get any ideas, Rutz explains.
Eventually, each young ‘alala picked up a stick to search for food.
The study authors could find no documented cases of Hawaiian crows using tools in the wild, except for one passing mention of a bird carrying a twig in its bill even though the nest-building season was over. They sometimes also exhibit meta-tool usage – they use tools to create other tools, something which requires very complex cognitive abilities. The “birds routinely selected tools of appropriate dimensions, replaced unsuitable tools, and transported non-supplied sticks to the log”. The big question was why they, but apparently no other members of the crow family (‘corvids’), had evolved such technological prowess.
The study adds to a growing database of knowledge around tool use, which could eventually lead to a greater understanding of the evolution of this ability in primates.
Scientists went with the first option, and half a century later, the list of tool users has expanded to include other primates, elephants, dolphins and sea otters, among others. Furthermore, there are fewer predators on these remote islands, so the crows can take the time to sit and focus on poking around a crevice without having to be so vigilant.
“The plot is thickening that something is going on on remote tropical islands”, Rutz said. Why do some crows use tools and others do not? But both species live on tropical islands, which could offer scientists a clue.
Rutz called up the programme manager at a captive breeding facility in Hawaii run by the San Diego Zoo.
This study began on a hunch.
By searching for this tell-tale sign amongst some of the lesser-known corvid species, Dr. Rutz and co-authors quickly homed in on a particularly promising candidate for further investigation – the Hawaiian crow.
For many years, scientists have been baffled by New Caledonian crows’ sophisticated tool-making skills.
Mentioning about the large, all-black Hawaiian crow, they are said to have a straight, shark beak, having small eyes and are forward-facing.
“Although the “Alalā became extinct in the wild in the early 2000s, and now survives only in captivity, at least two lines of evidence suggest that tool use is part of the species” natural behavioral repertoire”, the researchers said. “There are more than 40 species of crows and ravens around the world and many of them are poorly studied”.
“Now we can cautiously start constructing evolutionary arguments about the origins of tool use”, Rutz said. But now scientists can be a little more intentional in their search.
“This is really not just about crows, and this is not really just about tool use”, Shumaker says. Why did humans become so extraordinarily – and uniquely – handy?
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In other words, the birds are probably predisposed to be curious about objects – not unlike human toddlers.
