Crows’ specialised bill might explain clever tool skills
Thu Mar 10 2016 13:00:00 GMT+1300 (New Zealand Daylight Time)
Crows’ specialised bill might explain clever tool skills
10 March 2016
New Caledonia crow with panadus stick. Photo: Mick Sibley, University of Auckland
Famed for their intelligence, the New Caledonian crow is the only other animal on earth that makes complex tools with features such as hooks. But why and how this sophisticated tool-making ability evolved has long puzzled scientists.
Now a new piece of the puzzle has fallen into place: a team of international researchers has discovered that the New Caledonian crow’s bill is not only different to the bills of its close relatives, it may be unique in the bird world.
The team, including Senior Research Fellow Gavin Hunt from the University of Auckland’s School of Psychology, used shape analysis and CT scanning to compare the shape and structure of the New Caledonian crow’s bill with some of its crow relatives and a woodpecker species with a similar foraging niche
The team found the New Caledonian crow’s bill is shorter, stouter and straighter than the bills of the other species, which included the Japanese large-billed crow and the rook. The cutting edge of the upper bill is very straight, but it is upturned at the front of the lower bill.
These features give the birds not only a vice-like grip, but enable them to efficiently guide the tool tip with sharp binocular vision as they use the tool to forage for food.
“No other crow species can hold a tool as effectively as a New Caledonian crow,” Dr Hunt says. “This study shows that the novel bill contributes to the birds’ ability to use and probably make tools. We argue that it became specialised for tool manipulation once the birds began using tools, and that this enhanced tool manipulation ability may have allowed the crows to make more complex tools.
“This provides some evidence that physical changes were evolutionarily selected in a nonhuman species to enhance tool skills before it increased the sophistication of its tools. It also suggests that New Caledonian crows have been evolving their tool use over possibly millions of years, as humans have.”
New Caledonian crows make and use simple tools to forage for food. Stripping the leaf blade from the stem with their bills, they grip the leaf stem and poke it into tree burrows fishing for grubs and beetles.
Clever use of the tools includes poking them into the burrows of large longhorn grubs so that it is irritates the grubs enough to make them clamp onto the end of the stick. The grubs are then hoisted to the surface.
New Caledonian crows on the island of Grande Terre in New Caledonia also make two types of complex hook tool. The first by cutting shapes out of the barbed leaves of the Pandanus plant. The second is a crochet-hook-like tool made from forked twigs where the crows actually form the hooks themselves. These tools are used to extract insects from their hiding places in vegetation.
he research is published in Nature’s Scientific Reports.
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