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| Last Updated:: 13/05/2014

Basic information on birds

What is a Bird?

A bird has been described as a 'Feathered Biped'. This 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 changes 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 reflect 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 or Grebe with the peculiar, narrow. hairlike. 'double' feathers of the Cassowary to be seen in any zoo. Except in the Flightless Birds such as the last named, the Ostrich and the Penguin (Ralirae and Sphenici) whose feathers grow more or less evenly over the entire surface of the body, the growth of feathers is restricted only to well-defined patches or tracts known as pterylae on various parts of the body, whence they fall over and evenly cover the adjoining naked interspaces or apteria. A study of the arrangement of the feather tracts (pterylosis) which varies in the different orders, families, and even species, is of great importance in determining the natural relationships of different birds.

The feathers covering the body of a bird fall into 3 classes: (I) the ordinary outside feathers known as 'contour feathers' or pennae whether covering the body as a whole or specialised as pinions or flight feathers (remiges) or as tail feathers (retrices) which serve as rudder and brake: (2) the fluffy 'down feathers' or plumulae hidden by the 'contour feathers' and comparable to flannel underclothing, whether 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 birds, about 38°-44°C., is higher than that of most mammals. Assisted by their non-conducting covering of feathers birds are able to withstand great extremes 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°C on the burning desert sands or 40°C 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 air sacs as fast as it is produced. For one of the functions of the 'air sacs' - a feature peculiar to birds and found in various parts within the body - is to promote internal perspiration. Water vapour diffuses from the blood into these cavities and passes out by way of the lungs, with which they are indirectly connected.

In addition to these two cardinal attributes, warm-bloodedness and insulated feather covering, birds as a class possess certain well-marked characteristics which equip them pre-eminently for a life in the air. In India we have at present no indigenous flightless birds like the Ostrich or the Penguin, so these need not be considered here. The forelimbs of birds, which correspond to 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 running into them which, as mentioned above, function principally as accessory respiratory organs. This makes for lightness without sacrificing strength, and is a special adaptation to facilitate aerial locomotion. Modifications in the structure of the breast bone, pectoral girdle and other parts of the skeleton, and the enormously developed breast muscles enable a bird to fly in the air. It has been estimated from analogy with birds that a man, to be able to lift himself off the ground by his own effort, would require breast muscles at least 1.2 m deep! There is, moreover, a general tendency for various bones to fuse with each other, conducing to increased rigidity of the skeletal frame - also a factor of great importance in flight. As a whole the perfectly streamlined spindle-shaped body of a bird is designed to offer the minimum resistance to the wind. On account of their warm-bloodedness coupled with these peculiar facilities for locomotion with which Nature has endowed them, birds enjoy a wider distribution on the earth than any other class of animals. They cross ocean barriers and find their way to remote regions and isolated islands, and exist under physical conditions where their cold-blooded relatives must perish. It is also this power of swift and sustained flight that enables birds living in northern lands to migrate periodically over enormous distances in order to escape from the rigours of winter - shortening days and dwindling food supply – to warmer and more hospitable climes.

Birds are believed to have sprung from reptilian ancestors in bygone aeons. At first sight this appears a far-fetched notion, for on the face of it there seems little in common between the grovelling cold-blooded reptile and the graceful, soaring warm-blooded bird. But palaeontological evidence, supplied chiefly by the earliest fossil of an undoubted bird to which we have access – the Archaeopteryx :- and 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 the backbone, for instance, and the nucleated red blood corpuscles of the bird are distinctly reptilian in character. To this may be added the fact that birds lay eggs which in many cases closely resemble those of reptiles in appearance and composition, and that the development of the respective embryos up to a point is identical. In the majority of birds scales are present on the tarsus and toes which are identical with the scales of reptiles. In some birds, like sandgrouse and certain eagles and owls, the legs are covered with feathers. a fact which suggests that feathers are modified scales and that the two may be interchangeable. The outer covering of the bills of certain birds. for example the Puffin (Fractercula arctuca), is shed annually after breeding in the same way as the slough in reptiles. The periodical moulting of birds is also essentially the same process as the sloughing of reptiles. In short, birds may reasonably be considered to be extremely modified reptiles, and according to the widely accepted classification of the great scientist T.H. Huxley, the two classes together form the division of vertebrates termed Sauropsida.

Of the senses, those of Sight and Hearing are most highly developed in birds, that of Taste is comparatively poor, while Smell is practically absent. In rapid accommodation of the eye, the bird surpasses all other creatures. The focus can be altered from a distant object to a near one almost instantaneously; as an American naturalist puts it, 'in a fraction of time it (the eye) can change itself from a telescope to a microscope'.

For the safety of their eggs and young, birds build nests which may range from a simple scrape in the ground, as of the Lapwing, to such elaborate structures as the compactly woven nest of the Weaver Bird. With rarc exceptions they incubate the eggs with the heat of their own bodies and show considerable solicitude for the young until they are able to fend for themselves. Careful experiments suggest however, that in all the seemingly intelligent and purposeful actions of nesting birds, in the solicitude they display for the welfare of their young and in the tactics they employ when the latter are in danger. Instinct and not intelligence is the primary operating factor. The power of reasoning and the ability to meet new situations and overcome obstacles beyond the simplest are non-existent. It is good therefore always to bear this in mind when studying birds, and to remember that their actions and behaviour cannot be judged purely by comparison with human standards and emotions.

The total number of bird species known to science as inhabiting the earth today has been estimated as about 8600. If subspecies or geographical races are taken into account the figure would rise to nearly 30,000.

For its size, the erstwhile 'Indian Empire' or 'British India', in which, besides Pakistan and Burma it was customary for biological considerations to include Sri Lanka as well, contains one of the richest and most varied avifaunas on the face of the globe. Covering some 40 degrees of latitude and about the same of longitude, it encloses within its boundaries a vast diversity of climate and physical features. These range from the dry, scorching sandy deserts of Sind and Rajasthan and the humid evergreen rain forests of Assam and the southern Western Ghats to the region of glaciers and eternal snow in the mighty Himalayas. Smooth wide spaces of depressed river basins, either sandy, dry and sun-scorched, or cultivated, or water-logged under a steamy moisture-laden atmosphere (the terai) lie along the base of the northern ramparts. The great central Indian and Deccan plateaux succeed the fertile alluvial Gangetic Plain and are flanked on the west by the broken crags and castellated outlines of the ridges of the Western Ghats which overlook the Arabian Sea and continue southward in gentle, smoothly rounded slopes of green uplands - the Nilgiri and other hills of southern India.

This vast subcontinent - two-thirds of Europe in superficial area - with its extensive coastline, affords suitable living conditions to a great variety of feathered inhabitants. The second edition of the FAUNA OF BRITISH INDIA series on Birds enumerated some 2400 forms (species and subspecies). The latest checklist, A SYNOPSIS OF THE BIRDS OF INDIA AND PAKISTAN (which excludes Burma) lists 2061 forms of which over 300 are winter visitors, chiefly from the Palaearctic Region to the north.  The area as a whole falls into the zoogeographical division of the earth known as the Oriental Region. For the sake of convenience it has been split up (Blanford. Phil. Trans. of the Royal Soc. Vol. 194, 1901, pp.335-436) into 5 primary subdivisions as under:

a) The Indo-Gangetic Plain extending across the whole of northern India from the Arabian Sea to the Bay of Bengal. Its boundaries run up the hill ranges from Karachi to Peshawar, thence along the outer spurs of the Himalayas to Bhutan, and thence roughly southward to east of the Sundarbans. The southern boundary takes a line from the Rann of Kutch to Delhi and from about Agra to Rajmahal whence it goes south to the Bat of Bengal.

b) Peninsular India, southward of the above area.

c) Sri Lanka.

d) The Himalayas including the whole area of the mountain ranges from their foothills up to the limit of tree-growth.

e) Assam (and Myanmar). 

The Punjab, Sind and Rajasthan, however, have a fauna differing considerably from that of the other parts of India and resembling that found in W. Asia and N. Africa, whilst the animals of the Higher Himalayas (above the tree-line) and the Upper Indus Valley resemble those of central Asia. Both these areas belong to the zoogeographical region which extends over the greater part of Asia and all Europe, known as the Palaearctic.

A still further splitting of the fauna within these broad sub-divisions on the basis of ecological or environmental factors is clearly desirable. A scrutiny shows that there is a close similarity between the fauna and flora of those regions in which the incidence of the Southwest Monsoon is heaviest, namely the Himalayas east of Sikkim and the hilly portions of Assam and Myanmar on the one hand and the southwestern corner of the Indian peninsula, south of about Goa together with the southwestern portions of Ceylon, on the other. On account of the similar physical configuration of all these areas and their geographical position relative to the strike of the SW monsoon currents, they are areas of heavy rainfall and excessive humidity. These, precisely, are two of the most important factors that regulate the character of the vegetation. Similarity in vegetation is a striking feature of these heavy rainfall areas. As would be expected, this similarity extends to the insect forms dependent upon the plants, which in turn conduce to similarity in the birds predatory upon them. It has therefore been suggested that all these parallel areas, far-flung though they be, are perhaps better lumped together in one zoogeographical subdivision.

There are certain biological axioms of more or less universal application which are found to hold good in the case of our Indian avifauna also. They are of great importance, particularly in view of the modern practice of recognizing geographical variations and races. A cursory glance through any well-arranged museum collection or through the description of geographical races in any up-to-date work on systematic ornithology reveals the fact that the largest race of a bird species - this is true of other warm-blooded animals as well - is, with rare exceptions, found inhabiting the cooler part of its distributional range while the smallest inhabits the warmer. Parallel with this axiom is the fact that in the Northern Hemisphere races occupying the cooler (northern) portions of the range of a species tend to lay larger clutches of eggs than those occupying warmer (southern) parts. Furthermore, it is well known that of a given species the races that inhabit desert areas

are always pale or sandy-coloured whereas those living under the influence of heavy rainfall, in well-wooded or humid tracts, tend to be darker in coloration. This is true not only of individual races and species but also of the entire aspect of the avifauna of these tracts as a whole. What the precise factors are that bring about these changes in coloration, and the manner of their operation, we do not know. That humidity has to do with increased pigmentation is clear enough, and it has recently been suggested that the reduced force of ultraviolet rays due to water vapour suspended in the air may account for the darkening.

A few remarks with regard to the classification of birds seem called for in the interest of the beginner. It will be observed that after the English or trivial name of each species 'n the following pages, there appear two Latin names. The practice of employing a uniform Latin terminology is current throughout the modern scientific world. It is a boon to workers in different countries since it is more or less constant and enables the reader of one nation to understand what the writer of another is talking about. To take an example: What the Englishman calls Hoopoe is Wiedehopf to the German. A Pole knows the bird as something else - doubtless with a good many c's, z's, s's and other consonants in bewildering juxtaposition - while the Russian has yet another equally fantastic looking name for it. A fair working knowledge of a language seldom implies a familiarity with popular names as of birds, for instance, many of which often are of purely local or colloquial applications. 

Thus it is possible that while the Englishman may follow more or less all he reads in German about the Wiedehopf he may still be left in some doubt as to the exact identity of the bird. The international Latin name Upupa epops after the English or Polish or Russian name will leave no doubt as to what species is meant.

In the above combination the first name Upupa denotes the Genus of the bird corresponding roughly, in everyday human terms, to the surname. The second name epops indicates the Species and corresponds, so to say, to the Christian name. Modern trend of scientific usage has tended to split up the Species further into smaller units called Geographical Races or Subspecies. An example will clarify what this means: It will be admitted that all the peoples living in India are human and belong to one and the same human species. Yet a casual glance is enough to show that the Punjabi is a very different type in build and physiognomy from the dweller in Madras. The differences, though small, are too obvious to be overlooked. They are primarily the result of environment which includes not only climatic conditions of heat and cold, dampness and dryness, but also of diet and many other subtle factors working unceasingly upon the organism in direct or indirect ways. Thus while retaining all our inhabitants under the human species, when you talk of the Madrasi or the Punjabi you automatically recognize the sum total of the differences wrought in either by his particular environment.

A comparative study of birds reveals that there are similar minor but well-marked and readily recognizable differences in size, coloration and other details in those species which range over a wide area and live under diversified natural conditions, or which have been subjected to prolonged isolation as on oceanic islands, or through other causes. It is important for science that those differences should be duly recognized and catalogued since they facilitate the study of speciation and evolution. This recognition is signified by adding a third Latin name to the two already existing, to designate the Geographical Race or Subspecies. Thus, for example the House Crow, Corvus splendens, has been subdivided on the basis of constant differences in size and coloration brought about in the different portions of the 'Indian Empire' it occupies as follows:

Corvus splendens splendens (the nominate race), Common House Crow

Corvus splendens zugmayeri, Sind House Crow

Corvus splendens insolens, Burmese House Crow

Corvus splendens protegatus, Ceylon House Crow

Barring restricted areas and particular groups of birds which still require careful collecting and working out, we can now claim to have a sufficiency of dead ornithological material from India in the great museums of the world to satisfy the needs of even an exacting taxonomist. Most bird lovers in this country possess neither the inclination, training, nor facilities for making any substantial additions to our knowledge of systematics. Speaking generally, therefore, Indian systematic ornithology is best left in the hands of the specialist or museum worker who has the necessary material and facilities at his command. Our greatest need today is for careful and rational field work on living birds in their natural environment. or what is known as Bird Ecology. It is a virgin field; both the serious student and the intelligent amateur can contribute towards building up this knowledge. A great many biological problems await solution by intensive ecological study. This is a line of field research that may be commended to workers in India; it will afford infinitely more pleasure and is capable of achieving results of much greater value and usefulness than the mere collecting and labelling of skins.

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 far-flung corners of the country that it might perhaps be as well to devote a little space to them here.

Q. What is the largest Indian bird, and what the smallest?

A. It is not easy to say which particular one is the largest, but amongst the upper ten are certainly the Sarus Crane and the Himalayan Bearded Vulture or Lammergeier. The former stands the height of a man; the latter has a wing spread of over 8 feet. Amongst our smallest birds are the flowerpeckers, e.g. Tickell's Flowerpecker scarcely bigger than a normal thumb.

Q. What is our most beautiful bird?

A. 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 resident in areas of humid evergreen forest, possess extraordinarily brilliant plumage. As a family, the pheasants occupy a high place for colour and brilliancy of plumage and adornment possessed by the cocks of most species. At the bottom of the size ladder come the sunbirds - tiny creatures about half the size of the House Sparrow or less - whose glistening resplendent plumage scintillating in the bright sunshine as they flit from flower to flower or dart from one forest glade to another, transforms them into living gems.

Q. What is our commonest bird, and what our rarest?

A. The answer depends largely on what part of the country you live in. But for India as a whole, perhaps the House Crow and the Sparrow would be hard to beat for commonness and abundance. They have followed Man everywhere - up in the hills and out in the desert - wherever his ingenuity has created liveable conditions for himself. Next in abundance come birds like Mynas and Bulbuls which though not wholly commensal on Man are yet quick to profit by his presence and activities. Perhaps the three rarest birds in India at present are the Mountain Quail (Ophrysia superciliosa), Jerdon's Courser (Cursorius bitorquatus), and the Pinkheaded Duck (RhodQnessa caryophyllacea), all illustrated and described. The first has not been met with since 1876 and all attempts to re-discover them have ended in failure. The second which had not been seen since 1900 was rediscovered in the Lankamalai Sanctuary of Andhra Pradesh in 1986 by Dr Bharat Bhushan, a young scientist of the BNHS working on a project on endangered and rare species of birds. The fate of the Pinkheaded Duck is also shrouded in mystery and to all appearances the species has become extinct. The last example shot was in 1935, and though it has since been reported off and on as seen by sportsmen, in all the cases investigated these reports have proved unreliable, the bird actually seen being the Redcrested Pochard.

Q. Do birds have a language?

A. They certainly have, if by language is meant that they can communicate with and understand one another. It consists not of speech as we know it, but of simple sounds and actions and enables birds - especially the more sociable ones - to maintain contact amongst themselves and convey simple reactions such as those of pleasure, threat, alarm, invitation, and others. Several of these signals - vocal, behavioural, or a combination of the two - are understood not only by members of the same species but also by other birds generally, e.g. the alarm-notes and behaviour of many on the approach of a marauding hawk. To this extent Man can also claim to understand the language of birds; Solomon himself could hardly have done more. But the structure of a bird's brain suggests a comparatively low

level of intelligence and precludes the possibility of their holding regular conversations or expressing views and opinions as we humans are usually so ready to do!

Q. What is our most accomplished songster and talker?

A. Personally, for song I would give the palm to the Grey-winged Blackbird (Turdus boulboul) of the Himalayas. A number of its close relations, members of the Thrush family, including the Malabar Whistling Thrush and the Shama follow close on its heels. The best talker amongst our Indian birds is certainly the Hill Myna whose articulation of the human voice and speech is infinitely clearer and truer than that of the parakeets. The latter enjoy a wider reputation and are more generally kept as cage birds because they can be more readily procured.

Q. How long does a bird live?

A. The age-potential, or the age to which a bird is capable of living, of course varies according to species and the environment and conditions under which it lives. Reliable data concerning the life-span of wild birds in a state of nature are very difficult to obtain. It is only possible by the method of marking individual birds, particularly as nestlings. Most of the figures of age available are from birds in captivity and therefore living under somewhat unnatural conditions. It is known that within a group o[ related forms the larger the bird the longer its life, but outside related groups size does not seem to matter a great deal. An ostrich in captivity has lived for 40 years; a raven to 69 and another to 50. Passerine birds of about Sparrow size have occasionally reached 25 years, although normally their span is 5 to 8. A vulture attained 52, a horned owl 68, swan 25, pigeon 22 to 35, peacock 20. The longest lived wild birds in a natural state, as determined by the marking method, are: herring gull 36 years, oriole 8. pintail duck at least 13, grey heron about 16. blackbird 10, curlew  31Y2, kite 25-3/4, and swallow 16+. The common belief that crows are immortal is of course groundless, while there seems no proof for the popular assertion that vultures 'score centuries'.

- Dr. Sàlim Ali