Home Knowledge Nature Animals Vertebrates Birds

Birds are a Class of Animals which are characterised by being warm-blooded, egg-laying Vertebrates having Feathers and Forelimbs modified as Wings. There are around 10,000 living Species, making them the most varied of Tetrapod Vertebrates (animals having four feet or legs or leg-like appendages). The Class Aves approximately consists of 23 orders, 142 families, 2,057 genera. The fossil record indicates that Birds evolved from 'Theropod Dinosaurs' during the Jurassic Period, around 150–200 Ma (million years ago), and the earliest known Bird is the Late Jurassic Archaeopteryx, c 150–145 Ma. Most Palaeontologists regard Birds as the only Clade (biological group) of Dinosaurs to have survived the Cretaceous–Tertiary extinction event approximately 65.5 Ma.

Birds Types

Birds Evolution

Birds Classification

Birds Characteristics

Bird Reproduction

Many Species of Birds are of economic importance to Humans, mostly as sources of food acquired through hunting or farming. Some Species, particularly Songbirds and Parrots, are popular as Pets. Other uses include the harvesting of Guano (droppings) for use as a fertiliser. Birds figure prominently in all aspects of human culture from religion to poetry to popular music. About 120–130 Species have become extinct as a result of human activity since the 17th century, and hundreds more before then. Currently about 1,200 Species of Birds are threatened with extinction by human activities, though efforts are underway to protect them.

Birds are classified into two Superorders:

1. Palaeognathae - This Superorder is based on skeletal anatomy of the Palate, which is described as more primitive and Reptilian than that in other Birds.

Palaeognathae consists of two orders which comprise 49 existing Species.

   1. Struthioniformes - Ostriches, Emus, Kiwis etc.
   2. Tinamiformes - Tinamous.

2. Neognathae - This Superorder is based on fused metacarpals, an elongate third finger and 13 or fewer vertebrae in their skeletal system. Nearly all living Birds belong to the Superorder of Neognathae or 'New Jaws'. With their Keels, unlike the Ratites, they are known as Carinatae. The Passerines alone account for well over 5000 Species.

   1. Anseriformes - Waterfowl.
   2. Galliformes - Fowl.
   3. Charadriiformes - Gulls, Button-Quails, Plovers and Allies.
   4. Gaviiformes - Loons.
   5. Podicipediformes - Grebes.
   6. Procellariiformes - Albatrosses, Petrels, and Allies.
   7. Sphenisciformes - Penguins.
   8. Pelecaniformes - Pelicans and Allies.
   9. Phaethontiformes - Tropicbirds.
10. Ciconiiformes - Storks And Allies.
11. Cathartiformes - New World Vultures.
12. Phoenicopteriformes - Flamingos.
13. Falconiformes - Falcons, Eagles, Hawks and Allies.
14. Gruiformes - Cranes and Allies.
15. Pteroclidiformes - Sandgrouse.
16. Columbiformes - Doves and Pigeons.
17. Psittaciformes - Parrots and Allies.
18. Cuculiformes - Cuckoos and Turacos.
19. Opisthocomiformes - Hoatzin.
20. Strigiformes - Owls.
21. Caprimulgiformes - Nightjars and Allies.
22. Apodiformes - Swifts and Hummingbirds.
23. Coraciiformes - Kingfishers and Allies.
24. Piciformes - Woodpeckers and Allies.
25. Trogoniformes - Trogons.
26. Coliiformes - Mousebirds.
27. Passeriformes - Passerines.

History and Evolution of Birds

Based on fossil and biological evidence, most scientists accept that Birds are a specialized sub-group of Theropod Dinosaurs of the Triassic to Cretaceous with short forelimbs that walked or ran on strong hind legs. More specifically, they are members of 'Maniraptora', a group of Theropods which includes Dromaeosaurs and Oviraptorids, among others. The consensus view in contemporary Palaeontology is that the Birds, Aves, are the closest relatives of the Deinonychosaurs, which include Dromaeosaurids and Troodontids. Together, these three form a group called Paraves. The Late Jurassic 'Archaeopteryx' is well-known as one of the first transitional fossils to be found and it provided support for the theory of evolution in the late 19th century. Archaeopteryx has clearly Reptilian characteristics: teeth, clawed fingers, and a long, lizard-like tail, but it has finely preserved wings with flight feathers identical to those of modern Birds. It is not considered a direct ancestor of modern Birds, but is the oldest and most primitive known member of Aves or Avialae, and it is probably closely related to the real ancestor.

Birds diversified into a wide variety of forms during the Cretaceous Period. Many groups retained primitive characteristics, such as clawed wings and teeth, though the latter were lost independently in a number of Bird groups, including modern Birds (Neornithes). While the earliest forms, such as 'Archaeopteryx' and 'Jeholornis', retained the long bony tails of their ancestors, the tails of more advanced Birds were shortened with the advent of the 'Pygostyle Bone' in the Clade 'Pygostylia'. The first large, diverse lineage of 'Short-Tailed' Birds to evolve were the Enantiornithes, or Opposite Birds, so named because the construction of their shoulder bones was in reverse to that of modern Birds. The subclass Neornithes (modern birds) is, due to the discovery of 'Vegavis', now known to have evolved into some basic lineages by the end of the Cretaceous and is split into two Superorders, the 'Palaeognathae' and 'Neognathae'. The Paleognaths include the 'Tinamous' (small winged partridge like birds) of Central and South America and the 'Ratites' (flightless birds). The basal divergence from the remaining Neognathes was that of the Galloanserae, the Superorder containing the Anseriformes (ducks, geese, swans and screamers) and the Galliformes (the pheasants, grouse, and their allies, together with the mound builders and the guans and their allies). It is widely considered agreed that the Neornithes evolved in the Cretaceous, and that the split between the Galloanseri from other Neognathes occurred before the 'Cretaceous–Tertiary Extinction Event'.

Scientific Classification

Kingdom - Animalia.
Phylum - Chordata.
Subphylum - Vertebrata.
(unranked) - Amniota.
(unranked) - Diapsida.
(unranked) - Archosauria.
(unranked) - Dinosauria.
(unranked) - Theropoda.
Class - Aves.

Birds Characteristics & Physical Features

Presence of a Bill - A Bird's Bill is composed of a number of separate Horny Plates called 'Rhamphotheca' which are made of a protein called Keratin (the same protein that makes our hair and a rhinoceros' horn). The Rhamphotheca are fused together in most Birds but some evidence can be seen of their individual existence in the bill of the 'Fulmar', Fulmaris glacialis. Birds' Bills are relatively lightweight structures, weighing much less for their size than the comparable vertebrate jaws which involve bony supports and normally teeth. The top and bottom parts of a Bird's Bill are called 'Mandibles'. The Upper Bill or Mandible is also called the Maxilla. All Birds have their nostrils at the basal end of the top Mandible, except for the Kiwi where they are at the tip. The edges of the Bill are especially hard and sharp and are called 'Tomia', singular 'Tomium'. The part where the Two Mandibles meet at the hinge of the Bill is called the 'Commissure'. When Birds open their mouths it is the lower jaw that does most of the moving, most Birds can move the upper jaw to some extent though few groups like the Parrots have a flexible lower jaw. Birds have different shaped Bill's depending upon their diet, like short thin bills for insect eaters, short thick bills for seed eaters, long thin bills for probing flowers to feed on nectar, strong hooked bills for tearing meat etc.

Presence of Feathers - Feathers are the most basic characteristic of Birds. They facilitate flight, provide insulation that aids in thermoregulation, and are used in display, camouflage, and signalling. Feathers are epidermal growths attached to the skin and arise only in specific tracts of skin called 'Pterylae'. There are several types of feathers, each serving its own set of purposes. The arrangement and appearance of feathers on the body, called 'Plumage. Plumage is regularly Moulted. The standard Plumage of a Bird that has Moulted after breeding is known as the 'Non-Breeding Plumage' or 'Basic Plumage'. Breeding Plumages or variations of the 'Basic Plumage' are known as 'Alternate" Plumages'. Moulting patterns vary across Species. Moulting is annual in most Species, although some may have two moults a year. Flight is the primary means of locomotion for most Bird Species. They have modified forelimbs which are called Wings which enable them to fly. Each wing has a Central Vane (flattened web-like part of a feather) to hit the wind, composed of three limb bones, the 'Humerus, Ulna and Radius. The Hand, or Manus is composed of three digits which serves as an anchor for the Primaries, one of two groups of flight feathers responsible for the wing's airfoil shape. The other set of flight feathers, behind the carpal joint on the ulna, are called the Secondaries. The remaining feathers on the wing are known as Coverts, of which there are three sets. The wing sometimes has Vestigial Claws. In most Species these are lost by the time the Bird is adult like the Hoatzin chicks, but some retain these even in into adulthood by Secretary Bird, Screamers, Finfoots, Ostriches, several Swifts etc.

Light Weight Bones and Strong Skeleton - The strong skeleton of Birds consists of very lightweight bones. They have large 'Air-Filled Cavities', called 'Pneumatic Cavities' which connect with the respiratory system. These bones make flight more easy because of the reduced weight of the bones. Birds such as Swans have more vertebrae in their necks than those like Parrots who have very short necks. The flapping of wings to achieve flight requires huge muscles and these muscles need to be solidly attached to the skeleton. They also to generate tremendous stresses in the skeleton when working. A Bird gets around the first problem by having a greatly enlarged Sternum sometimes called a Keel or Carina which is also known as the Breast Plate. A Bird's Thorax is squat and compact in comparison with most other Vertebrates - this brings the operation of both the legs and the wings closer to the centre of gravity allowing them to work more efficiently. This also gives a Bird a better balance, important in both flight and bipedal (two legged) locomotion.

Bipeds - Biped means an Animal with two feet. All Birds are Bipeds when on the ground, a feature inherited from their Dinosaur ancestors. large Birds walk by raising one foot at a time while smaller Birds move by hopping on both legs simultaneously.

Heavy and Strong Leg Bones - The fundamental bones of a Bird's leg are the Femur, Tibia and Tarsus. Most Birds have four toes. The first points backwards in most Species and consists of a small Metatarsal and one Phalanx (toe bone). The second, third and fourth digits or toes are counted from the inside of the foot out and have 2, 3 and 4 Phalanges respectively. The fifth toe is lost completely except in some Birds where it has become a defensive spur, such as the chicken. The exact number of toes and their arrangement, as well as their proportions, varies from family to family. Ostriches have only 2 toes, while Rheas and Emus have three. The foot is a very important appendage for a Bird being the only source of support when standing, walking and running on a variety of surfaces. It also is a means of propulsion in aquatic Species, a major weapon in many predatory Species and for some Birds their equivalent of a hand, functioning to grasp and hold objects the Bird wishes to manipulate, mostly during feeding.

Five Boned Tongue - Birds have tongue which is composed of 5 bones which support and strengthen it, together they are called the 'Hyoid apparatus'. A Bird's tongue is generally harder and less flexible than most Mammals. Most Birds have a relatively simple tongue, a flat triangular blade in shape with a few backwardly pointing Papillae at the back of the mouth which help to ensure food only goes in one direction. However there is a great deal of variation in Bird tongues depending on the diet they eat, like in some fish-eating Birds such as Penguins the whole tongue is covered in backwardly pointing spikes which help in swallowing the fish. In other fish-eating Birds such as Cormorants, the tongue has been almost completely reduced.

Amniotic Eggs - All Birds lay Amniotic Eggs with hard shells made mostly of calcium carbonate. Hole and burrow nesting Species tend to lay white or pale eggs, while open nesters lay camouflaged eggs. There are many exceptions to this pattern, however; the ground-nesting Nightjars have pale eggs, and camouflage is instead provided by their plumage. Bird eggs are usually laid in a nest. Most Species create somewhat elaborate nests, which can be cups, domes, plates, beds scrapes, mounds, or burrows.

Weight - Weight of Birds vary from Species to Species. The 'Largest Extant Bird' weighs around 63 to 130 kilograms (140–290 lb) while the 'Smallest Extant Bird' weighs approximately 1.8 grams (0.063 oz).

Size - The 'Largest Extant Bird' is the Ostrich which stands at 2.75 m (9 ft) in Height. The 'Smallest Extant Bird' is 5 cm (2 in) in Length.

Geographical Range and Habitat

They inhabit ecosystems across the globe, from the Arctic to the Antarctic.

Diet - Birds' diets are varied and often include nectar, fruit, plants, seeds, carrion, and various small animals, including other Birds.

Bird Reproduction

95% of Bird Species are socially monogamous. These Species pair for at least the length of the breeding season or in some cases for several years or until the death of one mate. Monogamy allows for bi-parental care, which is especially important for Species in which Females require Males' assistance for successful brood-rearing. Among many socially monogamous Species, extra-pair copulation (infidelity) is common. Such behaviour typically occurs between dominant Males and Females paired with subordinate Males, but may also be the result of forced copulation in ducks and other Anatidaes (swan, goose etc.). Polygamous breeding systems arise when Females are able to raise broods without the help of Males. Although most Male Birds have no external sex organs, the Male does have two testes which become hundreds of times larger during the breeding season to produce sperm. The Female's ovaries also become larger, although only the left ovary actually functions. In the Males of Species without a phallus (reproductive organ), sperm is stored within the proctodeum compartment within the cloaca prior to copulation. Many Waterfowl and some other Birds, such as the Ostrich and Turkey, do possess a Phallus. Except during copulation, it is hidden within the proctodeum compartment within the cloaca, just inside the vent. During copulation, the Female moves her tail to the side and the Male either mounts the Female from behind or moves very close to her. He moves the opening of his cloaca, or vent, close to hers, so that the sperm can enter the Female's cloaca, in what is referred to as a 'Cloacal Kiss'. This can happen very fast, sometimes in less than one second. The sperm is stored in the Female's cloaca for anywhere from a week to a year, depending on the Species of Bird. Then, one by one, eggs will descend from the Female's ovaries and become fertilized by the Male's sperm, before being subsequently laid by the Female. The eggs will then continue their development in the nest. Incubation, which optimises temperature for chick development, usually begins after the last egg has been laid. In monogamous Species incubation duties are often shared, whereas in polygamous Species one parent is wholly responsible for incubation. After the eggs hatch, parent Birds provide varying degrees of care in terms of food and protection.