Birmingham & Black Country

Caledonian crow study reveals 'superior' bird's eye view

Caledonian Crow
Image caption Researchers say the birds can see their 'tool' in their beaks more clearly than other birds

There are many things that make us human but for scientists, the two most important factors are our use of tools and factors like opposable thumbs.

We appear to have evolved to be good at using tools and it is that which gave us the start we needed to become the dominant species on the planet.

But, scientists at the University of Birmingham and the University of St Andrews, in Scotland, have been looking to see if other species also show signs of having features that lend themselves to using tools.

They are particularly interested in the Caledonian crow which lives on the South Pacific island of New Caledonia.

These crows are unusual as they are some of the very few non-primates to use tools - in the wild they fashion small sticks and twigs into poking implements.

'Opposable thumb equivalent'

They then push these into holes in tree trunks to get at fat, juicy grubs living inside.

They do not spear or stab the grubs, instead they annoy them so much the grubs lash out at the stick with their powerful jaws.

But once the grubs have a grip the crows quickly remove the sticks with their lunch securely attached.

In 2010, scientists from New Zealand's University of Auckland found that the birds were able to use three tools in succession to reach some food.

So like us the crows use tools, but do they have an avian equivalent of our opposable thumbs?

Well the researchers believe they do.

They studied crows in the wild and in laboratory conditions and the Caledonian crow has a number of physical advantages other crows do not possess - they have a better field of vision.

'Substantially greater vision'

So they can clearly see their stick-tool when they hold it in their beaks.

The beaks themselves are also much straighter which also allows Caledonian crows a good view of the tool while they work to poke it into a narrow hole.

"We show that tool use in these birds is facilitated by an unusual visual-field topography and bill shape," a research spokesman said.

"Their visual field has substantially greater binocular overlap than that of any other bird species investigated to date.

Image caption Dr Chapell, part of the research team, says the birds have superior vision

"Furthermore, their unusually straight bill enables a stable grip on tools, and raises the tool tip into their visual field's binocular sector."

All crows have a reputation for being smart but, even if another species of crow observed the Caledonian crow in action and tried to copy its grub-on-a-stick technique it would fail. Its head, beak and eyes would be the wrong shape.

Dr Jackie Chappell, of the University of Birmingham, added: "They've got to be able to hold the tool steady and have got to grip on it but also be able to see what they are doing and see what the end of the tool is doing...particularly when probing in small holes."

So the big question is which evolved first - tool use or the shape of the Caledonian crow?

Sadly the researchers say since the fossil record is a little sparse for crows at the moment we just do not know.

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