Tag Archive for 'birds'

The secrets of bird colours

Diversity of non-iridescent or angle-independent feather barb structural colors in birds and the underlying nanoscale morphology of the color-producing (photonic) nanostructures revealed using electron microscopy and synchrotron small angle X-ray scattering (SAXS). Credits: Collage by Vinod Saranathan, photograph of Plum-throated Cotinga (Cotinga maynana) by Thomas Valqui.

For millennia birds have been prized, even hunted, for their beautiful plumage, but what makes their feathers so colorful? Read the fascinating work of physicist turned ornithologist Vinod Saranathan. At Phys.Org:

A new X-ray analysis of the structure of feathers from 230 bird species, led by Vinod Saranathan of Oxford University’s Department of Zoology, has revealed the nanostructures behind certain colours of feather, structures that could inspire new photonic devices.

A report of the research appears in the Journal of the Royal Society Interface.

“Pigments or dyes are the most common ways to make color in birds as in other organisms. Pigment molecules absorb certain portions of the white light spectrum and the portions that are not absorbed manifest as the colour we see,” Vinod tells me.

“For instance, melanosomes, granules filled with the pigment melanin, produce blacks, browns and reddish-browns in feathers, whereas other pigments such as carotenoids produce the majority of bright yellow, orange or reddish colors.”

He explains that parrots even have their own class of pigments (psittacofulvins) which give them their vivid yellow and red plumage.

“However, there are no known blue pigments found in vertebrates and the only known green pigment in birds is found in turacos, a group of birds endemic to sub-Saharan Africa,” Vinod says. More

Also read here

 

What’s happened to the seasons?

From temperate England to tropical India, the cycle of the seasons is fundamental to life. But lately they seem to have changed their patterns, with profound consequences. John Parker at Intelligent Life:

In the Indian state of Orissa, the black-headed oriole is the messenger of spring. It appears in the villages in January to greet the season’s start and flies away to the forest in March, signalling its end. Richard Mahapatra’s mother used the oriole’s fleeting appearance to teach her son about the natural rhythms of the world. “People like my mother remember six distinct seasons,” says Mahapatra, an environmental writer who now lives in New Delhi. After spring (basanta) and summer (grishma) came the rainy season (barsha). Between autumn (sarata) and winter (sisira) came a dewy period called hemanta. Each season lasted two months and the appearance of each was marked by religious festivals. “She had precise dates for their arrival and taught me how to look for signs of each.”

Damselflies gathered thickly a week before the rains began. Markers of the monsoon, they did not cluster at other times. The open-billed stork alighted on the tamarind tree on Akshaya Trutiya, a festival which usually fell in April or May and traditionally marked the start of the agricultural year. Farmers said that if you forgot the day, the bird would remind you, so predictable was its arrival. In the Mahapatra family’s garden, the nesting of bats in the peepal tree marked the onset of winter; when the tree flowered, it was midsummer.

Lately the heralds of the seasons have become unreliable. Damselflies swarm not only in the rainy season but in winter, the driest time of year. The stork no longer appears just on Akshaya Trutiya, but at other times, too. Villagers hear the song of the oriole in summer and the rainy season, not just spring. And this, Mahapatra says, is because spring is no longer a distinct season. Instead of six periods of equal length, Orissa now has two, a brief rainy season and a burning eight-month summer. Winter is a mild transition between the two, and spring, autumn and hemanta have been relegated to little-noticed interludes of a mere week or so.

“When I return home”, says Mahapatra, “my mother mourns the death of the seasons. More: