Birds
Modern birds can be traced back to reptilian ancestors. They are, in fact, probably the closest living relatives of the late dinosaurs. The Archaeopteryx, presently the oldest known bird, comes from the Late Jurassic period. While not a direct ancestor of today's modern birds, it remains the oldest known member of the Aves class. Its unique features, which blend elements of both reptilian and bird characteristics, provides us with one of the first transitional fossils to date. The Archaeopteryx displays teeth, clawed fingers and a lizard-like tail, all reptilian features. However, it, too, possesses wings and flight feathers, both features common to most of today's modern birds.
Birds are warm-blooded, oviparous vertebrates. While they are characterized as having wings, not all species are able to fly. The penguin, ostrich, emu and kiwi are all examples of flightless birds. Instead of flying, they rely on their abilities to swim or run. There are roughly forty known species of flightless birds surviving today.
Birds are found on all seven continents and in most terrestrial environments. There are approximately 10,000 species worldwide, and diversity is most prevalent in the tropical regions. Birds vary widely in size. They can be as minute as the two inch hummingbird, or as tall as a nine foot ostrich.
Social Behaviour in Birds
Birds are social creatures. They communicate through calls, songs and visual signals. Their social skills enable them to participate in a wide array of activities including cooperative hunting, and aiding in the care of young that are not their own, and flocking. The majority of birds are monogamous, in that they will remain with just one mate during a particular mating season. It is common, however, for birds to change mates in subsequent breeding seasons. Bird species that are monogamous during the entire course of their lifetime are very rare.
During mating season, the eggs are most commonly laid in a nest built by one or both parent birds. Eggs are protected and incubated while the chick develops inside. After hatching, most young birds rely on their parents for basic care for an extended period of time, until they have matured enough to care for themselves.
Feathers and Flight
The body of a bird is unique in that it has been adapted for flight behaviour. The structural body components which facilitate flight include the skeleton, which consists of extremely light-weight bones, the wings, which support the flight feathers, and a couple of large flight muscles, the pectoralis and the supracoracoideus.
Feathers, while aiding in flight, also provide insulation. Feathers, too, are used in camouflage, display and signalling behaviours. Birds groom their feathers daily, brushing away unwanted particles.
The wings are important in determining the type of flight a bird is capable of performing. It is the wing's size and shape that allows the bird to soar, flap, or perform both with equal ease. |
