Friday, 5 August 2016

Dozy Birds

I have a love-hate relationship with birds, the feathered kind.

In that luxurious state of early morning awakening there is nothing more beautiful than the dawn chorus.

On the downside I am terrorised by the regular thud of pigeons and gulls as they try to fly through my house having seen either a tantalising vision of paradise in the tinted double glazing or have imagined a short cut to the greenspace which is the park beyond.

I am fascinated by the commonly held belief that the birds of today were the dinosaurs of prehistoric times.

Take one particular species, the Frigatebird.

In a silhouette against the tropical skies that are their natural habitat they resemble a pterodactyl what with their wingspan of more than 2 metres, long deeply forked tail and hooked bills.



Their domain includes some of the most sparsely populated on the planet and as a consequence there has, until recently, been very little known about their life and behaviour.

That is surprising in that they were first described by a French naturalist  in 1667 and Christopher Columbus referred to them under their English name as "Man of War".

Fossillised remains have been found of the species from the Eocene Age, around 55 million years ago.

Two new and separate studies have illustrated some of the unique characteristics of the bird.

Tracking devices and heart rate monitors were attached to a couple of dozen Frigate birds in the Indian Ocean region. Flights paths of up to 300 miles a day were recorded and amongst the sample one of the birds stayed in the air for 2 months continuous.

This endurance in flight is explained by the astonishing fact that although having evolved in an aquatic environment the feathers of the bird are not waterproof and so there is no option of resting on the waves.

Tracking showed that the birds reached altitudes of 4000 metres (or around 12,000 feet) where the atmosphere is at freezing point are unknown for a tropical bird.

It was thought that enormous energy would have to be expended to attain such a height but the data from the heart rate monitors did not support this. It appears that the Frigate Bird is able to captitalise on the massive natural updraughts in Cumulus clouds over the oceans and their extensive wingspan is the perfect medium by which to ride on the thermals and thereby stay aloft for such long periods.

The study saw one bird glide for 40 miles without the need to flap its wings.

The same updraughts cause disturbance at sea level stirring up the activity of fish and their natural airborne predators. The Frigate Bird is rather lazy and will, rather than hunt for themselves, swoop down from their cruising altitude, steal and scavenge from other seabirds capitalising on the food fest or scoop up smaller flying fish in their large hooked bills.

With a lifespan as much as 40 years these majestic birds are amongst the real long distance travellers in the bird world.

A separate study has revealed perhaps an even more fascinating fact about an airborne existence, in that the Frigate Bird actually sleeps whilst in flight.

Sensors of brainwave activity saw an ability for the birds to switch off one half of their brains whilst being able to keep one eye open and maintain any wing motion. Alternate sides of the brain were activated dependant on the direction of circling in the Cumulus updraught or the brain could be completely shut down.

We are not talking about a complete shut down or the prospect of dozing birds filling the skies as the average rest period was about 12 seconds and the maximum, an extreme of 12 minutes. The study recorded only 42 minutes of rest per day but uninterrupted flights of up to 10 days entailed under one hour of sleep in some cases.

As humans we are well aware of the debilitating effect that a lack of sleep has on basic functions and so the performance of the Frigate bird with little or no rest and yet covering so many miles has excited considerable interest for any benefits to mankind.


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