Birds took flight over fight as their evolutionary defense

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."