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Animals

Birds took flight over fight as their evolutionary defense

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field of grass and flying birds

By Mark Waghorn via SWNS

Birds took to the sky instead of carrying weapons as evolutionary pressure demanded they could fly or fight - but not both, say scientists.

Beetles, deer and even crabs have natural armor - but our feathered friends don't.

Lead author Joao Menezes, a graduate student at the University of Massachusetts Amherst, said: "It is kind of puzzling.

"Birds have such spectacular songs, plumage and dances - but they mostly don't have specialized weapons.

"It's strange because dancing, singing, fancy feathers and fighting are all ways of successfully obtaining a mate, and often go together."

The finding in the journal Ecology Letters sheds fresh light on the mysteries of evolution.

A blend of natural and sexual selection made birds airborne. They developed wings - instead of bony spurs, explained the biologists.

It helps us better understand the enormous diversity of life on Earth, explained the biologists.

The key lay in the small number (1.7%) of birds that do in fact 'pack a punch' in the form of the bony spurs on their legs.

They include pheasants that are famously poor fliers - only managing short distances.

Unlike claws, the appendanges are straight or only slightly curved - making them suited to striking or stabbing.

In birds their function is for fighting, defence and territory marking - rather than predation.

Mr. Menezes and co-author Dr. Alexandre Palaoro, of Clemson University, South Carolina, then measured different species' flight aptitude.

The used the hand-wing index (HWI) - a vast annal that evaluates the efficiency of more than 10,000 birds.

The researchers then compared the two sets of data - and identified a striking link.

Mr. Menezes said: "The best fliers tend to lack spurs - and the most heavily armed fighters tend to struggle in the air."

A series of simulations and computer models suggested bony spurs impose a heavy evolutionary cost.

Plumage, dancing and the ability to sing are an advantage in sexual selection.

They help attract a mate - while spurs make flying a more energy-intensive activity.

The researchers believe spurs reduced an individual's ability to take off - or fly fast and far.

It is where natural selection kicks in - making birds more likely to get eaten or require more food to meet their daily requirements.

Unspurred counterparts can get away, eat less - and live to breed another day.

Added Mr. Menezes: "This helps explain why birds have an amazing range of plumage, song and dance - while almost totally lacking in the weaponry department."

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