#primary feathers

[biology-geology-beaches-india]

One never tires of seeing the aerial elegance of the beach hawk, its flight a poetry in motion. Note once again the splayed out primary feathers at each wing tip.

Sagar Nagar Beach, North Sector, October 12, 2010, Visakhapatnam, Andhra Pradesh.

[biology-geology-beaches-india]

A hawk executing beautiful aerial maneuvers in the skies above Sagar Nagar, North Sector; October 12, 2010, Visakhapatnam, Andhra Pradesh.

The flight feathers of birds - called remiges - come in two forms - primary feathers on the outer part of the wing, and secondary feathers on the inner part of the wing.

What is so striking about the primary feathers  - the finger-like projections seen in the photos -  is that they bear an emargination on the anterior portion of the feather vane and an indentation on the posterior portion of the same vane such that a visible notch separates each primary feather from the adjacent one - giving indeed that outstretched-splayed-finger configuration so dramatically brought out in the above photos when viewed in silhouette against the Sun.

The precise function of this notching is unclear, although theories abound.   Airplane wings do not bear such notches, those of birds do!!! and this coupled with the fact that airplane wings do not flap but those of birds do immediately gives us a clue as to the function of those gaps, those notches.

An airplane’s wing is designed just to glide, while that of a bird has to be a bit more versatile - it has to be capable of both flapping and gliding.

This immediately raises a problem in the evolutionary design of a bird’s wing. In order to glide far, over longer distances, with minimal effort, the wing must be broad and long - as witness the Andean Condor. But to FLAP such a huge set of wings - when flapping is required to gain altitude - would require extreme effort from the flight muscles, a power they simply would not be able to summon up since the air resistance to the flapping motion by a huge wing area has to be overcome.The problem is aggravated by the fact that the outer portion of the wing, by having what in Physics is called a MOMENT ARM - think of a lever, except that here it works to the detriment of the bird - would  further increase the amount of effort involved in flapping the wing.

The bird has come up with an ingenious solution - notching, which would reduce air resistance to the flapping motion by letting air through the extreme end of the wing, yet allow the wing to be broad of span for the prolonged graceful gliding.

It is a solution that is elegant not just figuratively, but literally, giving the bird wing a delicacy of lovely detail that no mundane airplane wing ever has!!, almost as though the bird were sensually touching and feeling and sensing the very air streaming by with its far-flung “fingers”!!!