A bird has been described as a “Feathered Biped”. The description is apt and precise, and can apply to no other animal.
Birds are vertebrate warm-blooded animals, i.e. whose temperature remains more or less constant and independent of the surrounding temperature. This is in contradistinction to reptiles. Amphibians and fishes which are cold blooded, i.e. of temperature that change with the hotness or coldness of their surroundings.
To assist in maintaining an even temperature, the body of a bird is covered with non-conducting feathers – its chief characteristic – which in details of structure and arrangement reflects the mode of life of the group to which the bird belongs. Compare for example the thick, soft, well-greased covering on the underside of an aquatic bird like a Duck with the peculiar, narrow, hair like, ‘double’ feathers of the Cassowary to be seen in any zoo.
The feather covering of the body of the word fall into 3 classes: (1) the ordinary outside feathers known as Contour feathers or pennae, whether covering the body as a whole or specialized as pinions or flight feathers (remiges) or as tail feathers (rectrices) which serve as rudder and brake: (2) the fluffy down feathers or plumulae hidden by the contour feathers and comparable to flannel underclothing, weather confined to nestlings or persisting throughout life; (3) the hair like Filo-plumes which are hardly seen until the other feathers have been plucked off. They are particularly noticeable, for instance, in a plucked pigeon.
The body temperature of bird, about 38 - 44 degree Celsius, is higher than that of most mammals. Assisted by their non-conducting covering of feathers birds are able to withstand great extreme of climate. As long as they can procure a sufficiency of food supply, or ‘fuel’ for the system, it makes little material difference to them whether the surrounding temperature is over 60 degree Celsius on the burning desert sand or 40 degree Celsius below zero in the icy frozen north. Their rate of metabolism is higher than that of mammals. They lack sweat glands. The extra heat generated by their extreme activity which would, under torrid climatic conditions result in overheating, fever, and death, is eliminated through the lungs and the air sacs as fast as it is produced. For one of the function of the ‘air sacs’ – a feature peculiar to birds and found in various parts within the body –is to promote internal perspiration. Water vapor diffuses through the blood in these cavities and passes out by way of the lungs, with which they are indirectly connected.
The forelimbs of birds, which correspond to the human arms or to the forelegs of quadrupeds, have been evolved to serve as perfect organs of propulsion through the air. Many of their larger bones are hollow and often have air sacs. This makes for lightness without sacrificing strength, and is a special adaptation to facilitate aerial locomotion. As a whole the perfectly streamlined spindle-shaped body of the bird is designed to offer the minimum resistance to the wind.
Birds are believed to have sprung from reptilian ancestors in bygone eras. Modern researches on the skeletal and other characteristics of our present-day birds tend in a great measure to support this belief. The method of articulation of the skull with backbone, for instance, and the nucleated red blood cell corpuscles of the bird is are distinctly reptilian in character. To this may be added the fact that birds lay eggs which in many cases resemble those of reptiles in appearance and composition, and that the development of the embryo up to a point is identical. In the majority of the birds scales are present on the tarsus and on the toes which are identical with the scales of reptiles.
Among the questions which the ornithologist in India is constantly being asked are the following. I have had to face them so frequently, from such a variety of people and in such a far-flung corners of the country that it might be perhaps be as well to devote a little space to them here.
Q what is the largest India bird, and what is the smallest?
A. It is not easy to say which particular one is the largest, but among the upper ten is certainly the Sarus Crane and Himalayan Bearded Vulture or Lammergeier. The former stands the height of man; the latter has a wing spread over 8 feet. Amongst our smallest birds are the flowerpeckers, e.g. Tickell’s Flowerpecker scarcely bigger than a normal thumb.
Sarus crane is a towering grey bird with a red head that stands as tall as a man. Its distinctive, trumpeting call carries over great distances. Sarus cranes can be sighted year-round in the lower parts of district Kangra of Himachal Pradesh. These birds here are more admired for its closeness to God.
The lammergeier is an impressive and unusual looking bird with a large tail and very wide, pointed wings that can spam up to three meters and which makes look like a gigantic falcon. On a clear day at least once you can see a pair flying over the valleys from the terrace of Wildflower Hall, and quietly soaring along the contours of the mountain slopes, their wings making a peculiar “purrrrr” sound heard when they fly overhead at close range.
Lammergeier feed on carcasses like other vultures but prefer bones to the meat. They pick up the bones, soar high in the air and then drop them onto rock. They can do this up to 50 times in necessary, until the bones splinters and the nutritious marrow inside is eaten. Digestive acids are said to be strong that shattered bones are completely digested.
Q What is our most beautiful bird?
A It is difficult to pick out any single species for the highest honour, and depends rather on individual tastes. A large number of birds of many different families, particularly those residents in the areas of humid evergreen forest, possess extraordinarily brilliant plumage.
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