The Origin of Birds

T.H. Huxley, the great evolutionist, called birds ‘glorified reptiles’ for quite clearly they have evolved from reptiles. Their early ancestors were similar to some of the dinosaurs of the Triassic period, millions of years ago. These were long-tailed, long-legged, lizard-like creatures, which ran about usually on their hind legs, flapping their wings and occasionally flying short distances. The Archaeopteryx, which is considered to be the oldest known bird, lived about 140 million years ago in the late Jurassic period; its fossils were found in 1861 and again in 1898 in Bavaria. It was about the size of a Magpie with a reptilean-type brain; it had jaws that had sockets to hold teeth, and a long bony tail. Although it is considered to be a bird, it had not adapted to flight in the same way as modern birds. Each of its ‘hands’ had three fingers and there was no sign of any fusion of the ‘hand’ and ‘wristbone’ as there is in modern species. Also its bones do not appear to have been honey-combed with air-spaces as they are in modern birds.

2008-08-20 London Wetlands Centre, Sir Peter S...

Image by Roy Stead via Flickr

Present day birds and reptiles still have common characteristics. Certain skeletal and muscular features are common to both; they both lay eggs and both have a horny protuberance on their bill or snout, known as the egg-tooth, which appears for a short time when the bird or reptile hatches. Both birds and reptiles lay eggs but birds’ eggs differ from those of reptiles in that many of them are coloured. Differences include the facts that birds usually guard their eggs whereas reptiles tend not to; young birds usually need care and feeding but the young of reptiles are independent at once; birds and mammals are warm-blooded but the body temperature of reptiles generally fluctuates with changes in air temperature, and therefore, they are more active on warm days. The feature which really sets birds apart from reptiles is that they are covered with feathers instead of scales, and that, with a few exceptions, they can fly.

Evolution is not something that only happened in the past; it is continuous throughout time. At present there are about 8,600 species of birds in the world and the process of natural selection is continuing with new species arising and others failing to compete. Natural selection is a process by which only those animals and plants best adapted to their environment survive. The young of all animals and plants, while conforming to the general pattern and shape of the species, also have their own individual characteristics. In a brood some will be bigger and stronger than others; various parts of their bodies may differ in size, some may have sharper sight or hearing than others allowing them to find food more easily or to avoid their enemies more quickly. Some may be able to react instinctively or more rapidly than others or to learn more quickly. Before long the young have to leave the care of their parents and find their own food, they may even have to fly long distances on migration, avoiding predatory birds on the way and a new set of hazards on their arrival in their winter quarters.

Some birds may not be so efficient at nesting, for instance, a pair of Goldfinches I once watched, failed, I was convinced, because of the male’s lack of attentiveness to the female. His failure to feed her when she was on the nest resulted in her having to leave to feed herself so often, that the eggs never hatched. All these natural factors and many others weed out the less able to ensure that generally the best adapted for the conditions of life, survive to reproduce.

Populations of a species which has a wide distribution will perhaps be affected by different environmental factors in various parts of its range which may result over the years in the evolution of a slightly different version of the same species. This difference may take the form of a change in size or colouring or even different habits. If sufficient numbers of a population exhibit these divergent characteristics they may be considered by taxonomists to merit a special sub-specific name. Finally, if this group is independent for long enough, it may develop sufficiently different characteristics from its parent stock and if, by chance, the two groups should meet again they would no longer be able to interbreed and will thus have become a distinct species.

Mute Swan Nest At Peter Scott's  Statue, Londo...

Image by Jim Linwood via Flickr

Now it so happens that over the years certain species have been unable to adapt to changes in the environment. Some of these changes have been hastened by man who has for agricultural reasons, perhaps, stripped vast stretches of forest of trees or drained marshes with the result that some populations of rare birds have been put in danger of extinction. Some, indeed, have become extinct because of man’s actions. However, while man’s activities have been harmful, we can now interfere with events and if some bird is in danger of extinction we can afford it some measure of protection. An example of this is the recent recovery of the population of the Hawaiian Goose, or Ne Ne. In 1949 only about thirty or forty of these geese were still known to exist having declined from a one-time estimated population of 5,000. Thanks to Sir Peter Scott, the Hawaiian authorities, New Zealand and the USA, the population has been able to steadily increase ever since.

27. September 2011 by admin
Categories: Lives of Birds | Tags: , , , | Comments Off on The Origin of Birds

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