For years, scientists believed that tools were used only by higher mammals, but now tool use — the process of utilizing an object to obtain food or achieve other goals — is understood to occur in more than just apes and elephants. While the vast majority of bird species are not known to use tools, the clever behavior has been observed in at least 33 bird families.
One of the earliest known tool users was observed by Charles Darwin on the Galápagos Islands in 1835. Twelve of the 13 species of Darwin’s Finches feed on seeds and show much variation in bill size as they adapt to different-sized seeds. The exception, the Woodpecker Finch, adapts to the niche normally occupied by woodpeckers (woodpeckers are not found on the Galápagos) and feeds on insect larvae found in crevices of tree bark and dead limbs.
The Woodpecker Finch has a typical short, finch-like tongue rather than an elongated woodpecker tongue designed to penetrate deep crevices or long burrows and withdraw grubs and other food items. To compensate, a Woodpecker Finch breaks off a cactus spine or small twig and, holding it in its bill, probes a cavity, scraping the insect larvae to the opening where its bill can reach.
A similar tool is used by the New Caledonian Crow on the Pacific island of New Caledonia. While Woodpecker Finches simply snap off a cactus spine at the desired length, New Caledonian Crows actually fashion twigs by bending them to form hooks or make serrated rakes from stiff leaves.
In a clever laboratory experiment with the crows, researchers presented the birds with two different pieces of wire — one straight and one hooked. Food was in a small basket with a wire handle on top and placed in a vertical clear tube. The only way to get the food was to select the hooked wire, insert it into the tube, and lift the food basket out. In one cage, the hooked wire had been inadvertently removed, and the bird had only a straight wire. To the astonishment of the biologists, the bird bent the wire to form a hook and promptly retrieved the food basket.
Carrion Crows of Japan were observed using “tools” in a very different way. The crows would drop walnuts on roadways and wait for them to be smashed by cars driving over them. In fact, crows were observed lined up with pedestrians at a traffic light. When the light changed, people walked across the street, and the crows hopped out to drop their walnuts and then hopped back to the sidewalk, waiting for the light to change, and, after another light change, would go back out and extract seeds from broken nuts. If walnuts were not smashed, the birds would move them slightly.
Herons using bait
Striated Herons (close relatives of our Green Herons) surprised observers in Japan when they picked up breadcrumbs from a park and dropped them into the water immediately below their fishing limb. The crumb served as bait, frequently drawing small fish into the heron’s attack zone. Herons have also been observed using bits of twigs and other vegetation as bait.
Not to be outdone in the prey-attracting category, Burrowing Owls sometimes gather animal dung from nearby fields and place it around their burrows. The “bait” attracts dung beetles, which can reach 2 centimeters in length and are a major prey item of the owls. In one study, biologists compared dung beetle remnants in regurgitated pellets of owls that had dung placed around their burrows with pellets from burrows without dung. Owls with dung near their burrows consumed 10 times more beetles than the others.
Perhaps the most amazing use of a tool for catching prey comes from Australia. In stories and traditional ceremonies, Aboriginal Australians in the northern part of the country have long referred to birds carrying fire. Recently, ornithologists published accounts of witnesses who seem to verify the legends, saying birds of prey use smoldering branches to spread fires and scare prey from safe cover.
Black Kites, Whistling Kites, and Brown Falcons are known to hunt small prey at the edges of brush fires. Ornithologist Bob Gosford, lead author of a 2017 paper in the Journal of Ethnobiology, says Black Kites and sometimes Brown Falcons “will pick up a firebrand or a stick not much bigger than your finger and carry it away to an unburnt area of grass and drop it in there to start a new fire.”
In the paper, Gosford writes: “Observers report both solo and cooperative attempts, often successful, to spread wildfires intentionally via single-occasion or repeated transport of burning sticks in talons or beaks. This behavior, often represented in sacred ceremonies, is widely known to
local people in the Northern Territory.”
It’s the first recorded instance of fire being used by animals other than humans.
Opening hard objects
Shellfish, such as clams, can be difficult for gulls to open. Several species of gull will grab a clam in its bill, fly up, and drop the clam onto rocks below.
Sometimes a hard object is too large to be carried aloft. The Egyptian Vulture faces this problem with ostrich eggs. And the ostrich shells are too thick for the vultures to break with their bills. They compensate by “throwing” stones at them. The vultures pick up the largest stones that can be held in their bills, raise their bills skyward, and forcefully throw them at the eggs.
Turtles are well protected by withdrawing into their shells. Eagles in Greece, however, have been observed carrying tortoises aloft to great heights and dropping them onto rocks.
The Greek playwright Aeschylus (525-456 B.C.), considered by some as the “father of tragedy,” returned to Sicily from a trip and died soon after. While that is not unusual, the manner of death was. It was reported that an eagle, mistaking Aeschylus’ bald head for a rock, dropped a tortoise on it to break the shell, but, instead, mortally wounded the man. While the accuracy of the story is debated, the widespread knowledge of the eagle behavior is not.
That birds should take up tool use is just another example of their amazing behavior. And it suggests that people traveling to Greece might want to pack a camouflage hat.
This article was first published in the “Amazing Birds” column in the January/February 2020 issue of BirdWatching magazine.