As regular CFZ-watchers will know, for some time Corinna has been doing a column for Animals & Men and a regular segment on On The Track... particularly about out-of-place birds and rare vagrants. There seem to be more and more bird stories from all over the world hitting the news these days so, to make room for them all - and to give them all equal and worthy coverage - she has set up this new blog to cover all things feathery and Fortean.

Saturday, 6 July 2013

Hummingbirds' wings 'shape-shift'

By Victoria Gill Science reporter, BBC News, Valencia, Spain

Footage shot with high-speed cameras has revealed how hummingbird wings bend and flex, to keep the birds in the air.

Masateru Maeda, a PhD student at Chiba University in Japan, captured the footage.

The ultimate aim of his measurements of the movements of the wings is to copy their function in the design of flying robots.

The scientist presented his findings at the Society for Experimental Biology's annual meeting in Valencia, Spain.

The researchers captured their footage at Tama Zoological park in Tokyo.

As birds and insects move through the air, their wings are held at a slight angle, which deflects the air downward.

This deflection means the air flows faster over the wing than underneath, causing air pressure to build up beneath the wings, while the pressure above the wings is reduced. It is this difference in pressure that produces lift.

Flapping creates an additional forward and upward force known as thrust, which counteracts the insect's weight and the "drag" of air resistance.

The downstroke or the flap is also called the "power stroke", as it provides the majority of the thrust. During this, the wing is angled downwards even more steeply.

You can imagine this stroke as a very brief downward dive through the air - it momentarily uses the weight of the animal's own weight in order to move forwards. But because the wings continue to generate lift, the creature remains airborne.

In each upstroke, the wing is slightly folded inwards to reduce resistance.

The team chose hummingbirds as their "wing model" because they can be studied so easily; they hover quite still as they feed on nectar.

"And they're very small," added Mr Maeda. "Larger birds that cannot hover have to be studied in wind tunnels."

But to get his footage, Mr Maeda had to work in the glasshouse of the zoo, which is kept at 35C for the birds and butterflies that live there.

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