Tuesday, May 16, 2006


Birds are warm-blooded, bipedal, oviparous vertebrate animals characterised by feathers fore limbs modified as wings. They differ in size ranging from small size to the huge birds such as ostrich. They are most diverse class of terrestrial vertebrates because they have 8,800-10,200 living bird species. They feed on nectar, plants, seeds, insects, rodents, fish and other birds.

Some birds are nocturnal (for example owls) and others are diurnal. Birds do migrate for long distance to find suitable living conditions. The Common characteristics of birds include a bony beak with no teeth, the laying of hard-shelled eggs, high metabolic rate, and a light but strong skeleton. Most birds are characterised by flight, though the ratites are flightless, and several other species, particularly on islands, have also lost this ability. Flightless birds include the penguins, ostrich, kiwi, and the extinct Dodo.

Birds have evolved some adaptations for flight purpose. Flight is the mode of locomotion used by most of the world’s bird species. This is important to birds for feeding, breeding and avoiding predators. Although the origin of bird flight is still not clear it believed that birds evolved this mechanism from small theropod dinosaurs. It seems likely that they evolved from ground living species, with developing after the evolution of feathers. Birds evolved this mechanism as a result of pursuing small airborne prey items such as insects and it became behaviour of adapting predator.

The flight is so energetically demanding birds have evolved several other adaptations to improve efficiency when flying. The most adaptation for flight on birds took place anatomically, modification, physiologically, on feathers and wings. Birds have hollow skeleton to reduce weight and many unnecessary bones have been lost for example the bony tail of the early bird Archaeopteryx, the toothed jaw of early birds which has been replaced by a light weight beak.
The birds have also adapted the vanes of the feathers with hook lets called barbules that zip them together, giving the feathers the strength needed to hold the airfoil. Birds evolved mono directional pulmonary system that provides the large quantities of oxygen required for the high respiration rate.

The large amounts of energy required for flight have led to the evolution of a mono directional pulmonary system, which provides the large quantities of oxygen required for the high respiration rate. However, birds do not suffer from the expected shortened life span as their cells have evolved a more efficient antioxidant system than those of other groups of animals.

Flight is more energetically expensive in larger birds, and many of the largest species fly by soaring (gliding without flapping their wings) most of the time. Many physiological adaptations have evolved that make flight more efficient. Birds evolved the digestive system which is simple but efficient (enabling them to pass food through their system quickly to minimize the extra weight of undigested food and the time it takes to extract energy from their food).

Today birds use flight for many purposes such foraging, to commute to feeding grounds and migrate between the seasons. It is still important in avoiding predators.


1. Wikipedia contributors. Bird flight [Internet]. Wikipedia, The Free Encyclopaedia; 2006 May 10, 20:11[cited 2006 May 11]. Available from:

Mr Lufuno Mukwevho
CSIR Pretoria
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