Here is a compilation of essays on the ‘Birds’ for class 11 and 12. Find paragraphs, long and short essays on the ‘Birds’ especially written for school and college students.
Essay on Birds
Essay Contents:
- Essay on the Origin of Birds
- Essay on the Characteristics of Birds
- Essay on the Systematic Position of Birds
- Essay on the General Characters of Birds
- Essay on the Representative Types of Birds
- Essay on the Modes of Flight in Birds
- Essay on the Beaks of Birds
- Essay on the Types of Feet Found in Birds
- Essay on the Palate in Birds
- Essay on the Economic Importance of Birds
Essay # 1. Origin of Birds:
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Aves or birds arose in the Jurassic from ornithischian dinosaurs and have many characters resembling those of reptiles; consequently the two classes together are called Sauropsida. Ornithischia was the second main group of dinosaurs and appeared later than sauropods. They possessed 4-radiate pelvis, with the pubis directed backwards and an extra prepubic bone pointing forwards.
Teeth were restricted to the hind part of the jaws, the front bearing a beak. At the front end of the lower jaw there was an extra bone (predentary). These were herbivorous forms and appeared in the Jurassic and achieved their maximum in the Cretaceous, by which time the sauropods had become less common.
The Triassic archosaurian reptiles (Subclass Archosauria- ruling reptiles) gave rise to two independent stocks that took to the air, called the pterodactyls and the birds. Both of these appear first in the Jurassic. The early archosaurs were bipedal animals, and the forelimbs were, therefore, free and available for use as wings. Other reptiles, such as Draco, develop a membrane between the limbs and the body to assist them in making soaring jumps. The flight of pterodactyl and birds may have originated like Draco or by flapping of the forelimbs during rapid running on the ground, then they became airborne for longer and longer periods.
Evolution of flight may have been different in both cases-the birds are fully bipedals, while the pterodactyls probably could not walk on their hindlegs and may have used the wing more for soaring than for flapping flight. Inspite of great differences there are interesting parallelism in the structure of the two groups viz., limb-bones became hollowed and light, skull bones fused and the jaws toothless and beaked. This parallelism in lives is known to be distinct showing remote common origin.
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The pterodactyls are most commonly found in the Jurassic strata, less often in Cretaceous. The characteristic features that have produced the pterodactyl structure from a thecodont ancestry may be described as a lengthening of the head and neck, shortening of the body and the tail lengthening of arms and especially of the fourth digit, shortening of the hindlimbs, and development of the ventral parts of the limb girdles.
There are many others in the soft parts which also occur during the evolution of birds, for instance, the pterodactyls were warm-blooded, fur on the legs and the wings. However, there is no evidence that they possessed feathers. The wing was a membrane (patagium). Olfactory lobes were reduced but larg e cerebral hemispheres, optic lobes and cerebellum as in birds.
Rhamphorhynchus of Jurassic is still of archosaurian structure, i.e., skull has two fossae and large teeth; humerus was short and strong, radius and ulna long, carpus with an extra “pteroid bone” in front, first three digits were short and hooked, fourth long supporting the wing and fifth absent. Hindlimb slender with five hooked digits. Tail was long ending in an expanded fin. Both girdles had well developed ventral regions and large sternum keeled in front. Scapula articulated with the vertebral column.
Pteranodon of Cretaceous showed further modifications, e.g.. trunk became shortened, forelimbs further lengthened, carpus being long, fourth digit much longer than the other three. Hindlimbs remained shortened and tail became very short. Teeth gradually lost and beak developed.
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In latest forms skull was drawn out backwards into a process. Pteranodon of late Cretaceous had a wing span of 8 metres Pterodactyl had a huge continuous membrane supported by a single finger. Pterodactyls were mostly marine. The largest flying birds alive today are the albatrosses, which use their great weight to gain height with the increasing velocity of wind a few metres above the sea.
It is possible that the pterodactyls used a similar method of soaring. They were presumably unable to compete with the birds, and died out at the end of Cretaceous, along with many other reptiles.
Nearly all the orders of present-day living birds had appeared by the end of Eocene. It is estimated that the total number of bird species that have existed is 154,000, of which 9,600 are alive today. The Pleistocene seems to have been a time of rapid formation of new species.
It was not until the Cretaceous that birds became modernised, this involved both physiological and morphological changes, such as constant temperature, fusion of skull bones, formation of pneumatic bones, fusion of vertebrae to form a synsacrum and a suppression of the tail .But birds have become highly modified due to an aerial life and show many differences from reptiles. Present-day living birds number 8,590 species, they are aerial, terrestrial and aquatic.
Essay # 2. Characteristics of Birds:
1. Aves or Birds are bipedal, endothermal craniates with an exoskeleton of epidermal feathers on the greater part of the body.
2. Body temperature is high and constant in correlation with their energy.
3. Beak and claws have horny sheath, and feet are covered with scales.
4. Bones of the skull undergo early ankylosis.
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5. There is a single occipital condyle.
6. The upper jaw is formed largely by premaxillae, and the lower jaw has 5 or 6 bones.
7. Forelimbs are modified to form wings with a carpo-metacarpus and only the first three digits of the hand.
8. Hindlimbs articulate far forwards to support the body weight in standing.
9. Head of the femur is at right angles to the shaft, there is a tibiotarsus and a tarso- metatarsus, there are never more than four digits, which are clawed.
10. Long bones are light with air spaces and no marrow.
11. The cervical and free thoracic vertebrae are usually heterocoelous. Several vertebrae fuse to form a synsacrum which fuses with the pelvic girdle.
12. Ribs are double-headed and have uncinate processes, both vertebral and sternal parts of ribs are bony.
13. The sternum has a ventral keel in flying birds.
14. Clavicle and interclavicle unite to form a furcula.
15. The ilium is very large, pubis and ischium are directed backwards, except in one case each they do not form pubic and ischiac symphyses.
16. The gullet is dilated into a crop, and the stomach is divided into a gizzard and a proventriculus.
17. Lungs are spongy and non-distensible, they are continued into air sacs.
18. Heart is four chambered and only the right aortic arch is present.
19. The skin is devoid of glands except an oil gland on the tail, and the tail is much reduced.
20. Cerebrum has large corpora striata, and optic lobes are lateral. The lumbar region of the spinal cord has a sinus rhomboidalis.
21. Eyes are well developed with a large pecten, they have sclerotic bones.
22. There are three-lobed metanephric kidneys, a urinary bladder is absent.
23. Right ovary and oviduct are usually atrophied.
24. They are oviparous with large yolky eggs enclosed in shell membranes and a hard shell, the embryo has an amnion, allantois, and yolk sac.
25. The young when hatched may be precocial or nidifugous being able to fend for themselves, or they may be altricial or nidicolous being naked and dependent on the parents for food for some time, in which case there is much parental care. Birds are noted for courtship, attachment to mates, nest building, and habit of migration in many.
Essay # 3. Systematic Position of Birds:
Phylum – Chordata
Group – Vertebrata
Subphylum – Gnathostomata
Superclass – Tetrapoda
Class – Aves
Subclass – Neornithes
Superorder – Neognathae
Order – Columbiformes
Genus – Columba
Species – livia
Essay # 4. General Characters of Birds:
1. Birds are feather-clad, warm-blooded, air-breathing, oviparous, bipedal flying vertebrates.
2. Body is roughly boat-shaped and divisible into head, neck, trunk and tail. Jaw bones projected to form toothless beak (bill). Tail is short and stumpy.
3. Limbs are two pairs. The forelimbs are modified into wings, each bearing three clawless digits and provided with feathers for flight. The hindlimbs are adapted for walking, running, scratching, perching, swimming or wading, and bearing four toes. First or hallux directed backward.
4. Exoskeleton is epidermal and horny. Feathers provide warmth. Legs are covered by scales. Claws on toes and sheath on beaks. No skin gland except the oil glands at the base of tail.
5. Skin is dry.
6. Pectoral muscles are well developed used for flight.
7. Endoskeleton. The bones, forming the skeleton, are spongy, light in weight containing air cavities. Long bones pneumatic and without marrow.
8. Skull is monocondylic having single rounded occipital condyle. Cranium large and sutures indistinct.
9. Lower jaw is composed of five or six bones.
10. Modern birds have no teeth. A horny beak is present.
11. Vertebral column short. Centra of vertebrae are heterocoelous. Cervical vertebrae with reduced pointed cervical ribs, first thoracic vertebrae free and some are fused together, last thoracic + sacral vertebrae, lumbars and anterior caudals are fused to form a synsacrum. The posterior caudal vertebrae are usually fused to form a pygostyle.
12. Vertebral ribs are double headed, provided with uncinate process.
13. Sternum is broad, usually with a longitudinal mid-ventral keel for the attachment of flight muscles.
14. Both clavicles and a single interclavicle are fused to form a U- or V-shaped furcula.
15. In pectoral girdle, the coracoid is usually more or less pillar-like and the scapula is sabre-shaped.
16. Pelvic girdle is large, elongated and fused with the synsacram along its entire length. Pubic and ischiatic symphysis absent and acetabulum is perforated.
17. Proximal carpals are free and distal carpals and metacarpals are united to form a carpo-metacarpus.
18. Proximal tarsals are fused with the tibia to form a tibio-tarsus and metatarsals with the distal tarsals to form the tarso-metatarsus.
19. In the leg, the ankle joint is inter-tarsal.
20. The gullet is dilated into a crop for the storage of food. Stomach is divided into a glandular proventriculus and a muscular gizzard. A pair of small rectal caeca are present at the junction of small intestine and rectum. Cloaca is three chambered.
21. Lungs are spongy and non-distensible with thin-walled air sacs.
22. The voice is produced by the syrinx situated at the junction of trachea with the bronchii. Lyrinx is without vocal cords.
23. The heart is four chambered. Sinus venosus and truncus arteriosus are absent. Only right aortic arch is present in the adult. Renal portal system is vestigial. RBCs are oval, nucleated and biconvex. Homoiothermous (warm blooded).
24. Kidneys are metanephric, three lobed and ureters open into the cloaca. Urinary bladder is absent. Nitrogenous wastes are uric acid (urecotelic).
25. Brain is smooth and large. The cerebral hemispheres and cerebellum are well developed and the optic lobes are displaced laterally. Olfactory lobes small with poorly developed sense of smell.
26. Eyes are large with nictitating membrane, pecten and surrounding sclerotic plates.
27. Sexes are separate and sexual dimorphism is well marked. Male has a pair of abdominal testes. Copulatory organ is absent except ratites and Anseriformes. Only left ovary is present. The right ovary and oviduct are more or less completely atrophied.
28. Fertilisation is internal. Oviparous. Ovum large containing much yolk invested with albumen, shell membranes and shell.
29. The embryo has an amnion, chorion, allantois and a large yolk sac. Newly hatched young is either precocious or nudifugous (able to run or swim and can obtain their own food) or altricious or nudicolous (more or less naked and depend on parents for their food).
30. Parental care is highly developed.
Essay # 5. Representative Types of Birds:
1. Archaeopteryx:
Two perfectly preserved specimens of Archaeopteryx (Fig. 27.1) were found in Bavaria in the fine grained lithographic limestone of the Upper Jurassic about 140 million years ago. It was discovered by Andreas Wagner in 1861. Another skeleton was found in 1877 and a third was also found in 1956 from the same place. Had not the impression of feathers been found they would have been taken for some bipedal diapsid reptile.
Archaeopteryx, like Seymouria, is an example of mosaic evolution. It is of the size of a crow with a long tapering tail and dwelt in forests; though the body was covered with feathers, its body axis was elongated like that of a lizard. It is an extinct bird and is a transitional stage showing characters of both reptiles and birds.
Reptilian Characters of Archaeopteryx:
Archaeopteryx presents striking affinities with reptiles which are given here:
1. The bones are solid with no air spaces.
2. The jaws have small equal conical enamel-crowned and thecodont teeth like those of reptiles. There are 26 teeth in the upper jaw and 6 in the lower.
3. The forelimbs are reptilian. There are three well-formed digits with separate phalanges, there are 2 phalanges in the first, 3 in the second and 4 in the third digit. The digits bear no feathers but project from the anterior margin of the wing end in curved claws.
4. There are three free metacarpals, there being no carpometacarpus.
5. The sternum is flat without keel.
6. The vertebral column is elongated and vertebrae are free and amphicoelous with simple concave articulation as in reptiles.
7. There is a sacrum of only 5 or 6 vertebrae as in dinosaurs.
8. The vertebrae bear thin, single-headed ribs with no uncinate processes.
9. Besides the cervical and thoracic ribs, there are abdominal ribs or gastralia in the ventral wall of the abdomen, as in Sphenodon and crocodilians.
10. The bones of the pelvic girdle are not fused, the ilium is long, the pubis is directed posteriorly and probably there is an ischiac symphysis.
11. Hindlimb has separate tibia and fibula of about equal size with no reduction in size of fibula.
12. Proximal tarsals are free.
13. There is an elongated tail with 20 free caudal vertebrae tapering gradually to the distal end, there being no pygostyle.
14. The cerebral hemispheres were smooth, long and narrow and cerebrum was small, thus, the brain is reptilian.
Avian Characters of Archaeopteryx:
1. The skull is large, monocondylic and bones are fused.
2. There is short blunt beak formed by elongation of both the jaws.
3. The eyes are large and avian with a ring of sclerotic bones.
4. Flight feathers are attached only to the back of ulna and manus, there are 6 to 7 primaries and 10 secondaries.
5. In the pectoral girdle the coracoid is small, scapula is slender and curved and they are at right angles as in birds.
6. There is U-shaped furcula formed by fused clavicles.
7. Distal tarsals are fused with the metatarsals to form a slender tarsometatarsus.
8. There are four clawed digits with 2, 3, 4, 5 phalanges, with the hallux small, directed backwards and opposable.
9. Rectrices are attached to both sides of the tail unlike any bird.
10. Recent studies have shown that Archaeopteryx was endothermal or warm-blooded as other birds.
Archaeopteryx could not fly efficiently but could only volplane, from tree to tree in forests, because the sternum is small, flat and without a keel, the wing spread is small, and it has an elongated, feathered lizard-like tail. It shows that birds arose from bipedal, arboreal ancestors and it also shows the gliding origin of flight in birds.
Significance of Archaeopteryx:
Many characteristics of birds show close resemblance to the archosaurian reptiles. Archaeopteryx had achieved some powers of flight or gliding, but they were less specialised for the purpose than are modern birds. The whole body axis was still elongated and lizard-like. Its fossil and other like fossils suggest that the birds arose from a race of bipedal arboreal reptiles, living in forests and accustomed to running, jumping and gliding among the branches.
There has been much controversy about the origin of flight, some maintaining that the earliest birds were terrestrial and used the wings to assist in running, leading eventually to a take-off, perhaps at first for short distances. A recent theory is that the enlarged feathers on the back of the hands may have served as nets to assist in catching insects.
Archaeopteryx showed both reptilian and avian characters. It was certainly not a bird like the modern birds and also it was not a true reptile. Except feathers it resembled to archosaurian reptiles. It was presumably not the immediate ancestor of modern birds. Its immediate descendants are also not known. It was distinctly separate from the birds due to presence of non-pneumatised bones, forelimb ended in 3 clawed digits, with separate metacarpals and phalanges and elongated tail.
Hesperornis and Ichthyornis, cretaceous birds, were distinctly birds, except they had reptile- like teeth. Hence, Archaeopteryx was placed in a separate subclass Archaeornithes since it had certain different characters not found in fossil birds and modern birds placed in Neornithes.
Essay # 6. Modes of Flight in Birds:
The modes of flight in birds are of three or four kinds. All these kinds of flight may be used at different times by the same bird. In all the types of flight, the tail helps to support and balance the body, serving as a rudder.
The tail feathers of pigeon act as rudder for vertical and lateral steering, elevating the tail produces an upward slant and lowering the tail a downward turning. Landing is achieved by lowering and fanning out the tail feathers which act as a break, then the legs are lowered and the pigeon drops on a perch.
The chief kinds of flights are as follows:
1. Gliding or Skimming:
The simplest and probably the most primitive mode of flight is gliding (Fig. 28.4A). Birds hold their wings spread, motionless and glide for a considerable distance without flapping them. Gliding depends for its movement on the velocity acquired by previous strokes, or by descending from a higher to a lower level or by making use of air-currents.
The gliding flight can be shown for a short time, bird soon loses velocity or height. Gliding flight can be readily observed in shore birds coming in for a landing; in ducks, gulls and herons over water, in swallows and swifts in the air, in pigeons gliding from their loft to the ground or in falcon swooping upon its quarry.
2. Soaring and Sailing:
This is the most remarkable and highly specialised mode of flight (Fig. 28.4B). This type of flight is illustrated by birds with a large wing-span, such as albatross, vulture, falcon, stork, crow, etc. The bird usually at a high level, describes great circles without any movement of the wings, whatsoever. The bird rises without loss of kinetic energy.
3. Flapping:
This is most common or ordinary mode of flight (Fig. 28.4C). All birds fly by flapping their wings up-and-down. Each flapping includes an effective downstroke and a recovery upstroke of the wings. To start with, the wings are held vertically and fully spread. In the downstroke, they move obliquely forward, downward and backward, their distal portions tilted upwards.
Thus, there is both lift and thrust. In the upstroke, the wings are partly folded and their primary feathers spread out for the air to slip through, thus making it easier to lift them. They move up and backwards. As a net result, the bird will be propelled forwards and sustained in the air.
The pigeon flies by flapping method. The flight includes the quick take-off by jump and flapping of wings in downward and backward stroke, which propel the bird forward, and by forward and upward movement of recovery stroke, this is done by bringing back the wing edgewise to the resistance of the air. The downward stroke of wings works as a lift force acting upwards.
The lift force is proportional to the speed, and the requirement for sustained flight in the air is that the bird should have sufficient speed to generate a lift force equal to its weight. The flow of air over the upper surface of wings reduces the pressure and provides a portion of the lift. By tilting the wing the pressure on the underside can be increased. Pigeons can beat their wings at least eight times in one second.
4. Hovering:
This is a peculiar kind of flopping flight. Support of weight without horizontal movement requires very much greater consumption of energy than forward flight and the largest humming birds weigh only 20 gm. The principle involved is also that used for short times by larger birds in take-off and landing.
Lift for weight support requires horizontal movements and since the wings beat in a plane perpendicular to the body, hovering is achieved essentially by holding the body vertically (Fig. 28.4D). In this way the humming birds can remain in one place in the air or even move backwards. The wings beat backwards and forwards, often as fast as 200 times a second.
Essay # 7. Beaks of Birds:
The entire modern world of Aves (birds) is characterised by the absence of teeth. Their absence is compensated by the development of horny sheaths called rhamphotheca for the jaws which constitute the beak. The beak is also referred to as bill. The upper and lower jaws are often described by naturalists as the upper and lower mandibles.
The sheath of each jaw in the majority of birds is entire, but in some it is composed of several pieces. The beak is essentially a structure to obtain food, to preen feathers, to collect nest materials to build the nest and also to act as the organ of defence.
The shape of the beak varies in different birds according to their feeding habits. Because of the functional diversities, the beaks have undergone extensive range of modifications in different birds. Figure 28.6 shows a few varieties of beaks in birds. Some of the most important and common types are described here.
1. Seed-Eating Beak (Seed-Crushing Beak):
(a) The seed-eating beaks are short, stout, conical and pointed at the tip.
(b) This type of beaks are characteristic of small seed-eating or graminivorous birds such as sparrows, finches and cardinals, etc.
(c) The weaker beaks are used to pierce the small seeds, while powerful beaks crush large, hard-shelled seeds, fruit stones, etc.
2. Cutting and Biting Beak:
(a) The cutting and biting type beaks are long and strong and provided with sharp horny edges,
(b) This type of beaks can be used for various purposes,
(c) These are found in crows (Corvus) and rovens, etc.
3. Fruit-Eating Beak:
(a) The fruit-eating beaks are large, sharp, powerful and hooked.
(b) The upper beak is movable on the skull and is well adapted for tearing fruits and gnawing hard nuts and seeds,
(c) Such beaks are found in parrots and cockatoos. In hornbills beak is large and heavy having cellular structure in its inner region that act as resonators to produce loud sound.
4. Piercing and Tearing Beak:
(a) The piercing and biting beaks are short, pointed, sharp-edged and hooked at the tip and are adapted for piercing and tearing the flesh into pieces.
(b) They are operated by well developed mandibular muscles,
(c) These are commonly found in carnivorous birds such as vultures, hawks, eagles, kites and owls.
5. Insectivorous Beak:
(a) The insectivorous beaks are found in swifts, swallows, flycatchers, night jars and hoopoe, etc.
(b) In hoopoe the beak is long, slender and slightly curved, adapted for turning the leaves and probing into soil for insect larvae, pupae and mites, etc.
In swallows, frog-mouth and swifts, the beak is small, wide and delicate to prey upon flying insects. In flycatchers, the beak is small, strong with notched mandibles at the tip end. Rictal bristles are also present at the base of the beak.
6. Fish-Catching Beak:
(a) The fish-catching beaks are long, powerful and sharply pointed found in storks, herons, kingfishers, etc.
(b) In cormorant the beak is slightly curved at the tip and have lateral tooth-like processes adapted for capturing the fish. In snake birds (Indian darters), these lateral tooth-like processes over the beaks are in the form of needle-like processes,
(c) In kingfisher the beak is long, powerful and sharply pointed to capture fish, frogs, tadpoles, molluscs and other aquatic animals.
7. Wood-Chiselling Beak:
(a) The wood-chiselling beaks are long, straight, stout and chisel-like and are strongly articulated with the skull,
(b) The skull bones are also thick and shock absorbent. Neck muscles are also strong,
(c) This type of beaks are used for chiselling and drilling into bark or wood of trees for the prey, e.g., insects and their larvae and for nest construction,
(d) It is commonly found in woodpeckers.
8. Mud-Probing Beak:
(a) This type of beaks are very long, slender and slightly curved to probe the mud deep for searching the aquatic worms and larvae,
(b) These are commonly found in stilts, snipes, sandpipers, jacanas, lapwings and curlews, etc.
9. Mud and Water Straining Beak:
(a) This type of beaks are broad and flat, and the margins of the jaws are provided with transverse lamellae or horny serrations making it an efficient filter or sieve,
(b) Because of the presence of transverse lamellae on the margin of jaws, the mud and water pass out leaving the food into the mouth,
(c) This type of beaks are commonly found in ducks, teals, geese and flamingos. In flamingo, the beak is distally decurved. The two halves of lower jaw are enlarged to form a wide cavity that is covered over by upper jaw.
10. Flower-Probing Beak:
(a) This type of beaks are long, narrow and pointed for probing flowers and for sucking honey,
(b) It is found in humming birds, which become stationary in air over the flowers for sucking honey. Their beaks are slightly decurved adapted for such function.
11. Pouched Beak:
(a) It is found in pelicans,
(b) The beak is large having a large gular pouch,
(c) The gular pouch is an extension of skin and attached to the mandible for storing engulfed fish.
12. Spatulate Beak:
(a) It is a characteristic of spoonbill,
(b) It is specially flattened throughout the length but ends in a broad spatulate or spoon-like expansion,
(c) The spatulate expansion is used for dabbling in mud and water in search of fish, tadpoles, worms, insects and other small aquatic animals.
Essay # 8. Types of Feet Found in Birds:
The feet of birds are also modified variously in accordance with the character of the environment and the manner of locomotion (Fig. 28.7).
1. Running or Cursorial Feet:
(a) In running birds, the legs are powerful and number of toes are reduced,
(b) The hind toe is elevated, reduced or absent,
(c) Ratites, e.g., Rhea, Emu and Cassowary and coursers, bustards are short-toed birds and having 3 toes directed forward. In ostrich the legs have only two toes, i.e., 3rd or middle toe and 4th or outer toe is smaller and devoid of nail.
2. Perching Feet:
(a) The perching type of feet are found in majority of birds (passer birds), e.g., sparrows, crows, bulbuls, koels, mynas and robins, etc.
(b) In this type of foot there are four movable toes, three toes in front are slender and the hind or hallux is long, strong and sharply clawed,
(c) Because of opposable toes these birds can fasten the foot to a branch of tree.
3. Climbing Feet:
(a) The climbing type of feet are found in parrots, woodpeckers and hoopoes,
(b) The feet are zygodactylous. The second and third toes are directed forwards, while the first and fourth toes are directed backwards,
(c) The foot is modified for grasping and especially adapted for climbing on vertical surfaces of trees and walls.
4. Clinging Feet:
(a) The clinging type of feet are found in martinets, swifts and humming birds,
(b) All the four toes are directed forwards and have long, sharp and curved claws,
(c) The foot is modified for clinging on the trees or any vertical surface while feeding.
5. Scratching Feet:
(a) The scratching type of feet are found in fowls, quails and pheasants.
(b) The feet are stout and provided with strong clawed toes,
(c) The second, third and fourth toes are directed forwards, while the first toe is directed backwards,
(d) The foot is modified for running as well as scratching the earth,
(e) In the male, the foot is usually provided with a pointed bony spur for fighting and for treading the females.
6. Raptorial Feet:
(a) The raptorial type of feet are found in predatory or carnivorous birds such as ospreys, hawks, kites, eagles, owls and vultures, etc.
(b) All the four toes are large and the hallux is strongly developed. The claws are large, strong, sharp and curved. The undersurface of all toes possesses large fleshy bulbs called tylari. These are well developed in hawks,
(c) In osprey and ketupa, tylari are absent but sharp denticulated spines are present which serve to the slippery creatures (fish),
(d) The foot is modified for grasping and holding the prey.
7. Swimming Feet:
In swimming birds the feet are modified in two ways, i.e., swimming and diving type and swimming and paddling type:
(a) Swimming and Diving Feet:
(i) In swimming and diving type of feet, toes are partially or completely webbed. These types of feet are found in coots and grebes. In these birds the web is lobate on the undersurface and the toes are free.
(ii) In grebes each toe is paddle-like bordered on either side by fleshy lobes of integument,
(iii) The nails are flat in a grebe and in coot slightly curved,
(iv) This type of feet are modified for swimming and diving in water.
(b) Swimming and Paddling Feet:
(i) Swimming and paddling type of feet are found in cormorants, pelicans, ducks and teels. Here the toes are webbed,
(ii) In cormorants and pelicans all the four toes are connected with tough web all along their length,
(iii) In ducks and teals the first toe in comparatively small and free, while three anterior toes are completely webbed.
8. Wadding Feet:
(a) The wadding type of feet are found in herons, jacanas, lapwing and snipes, etc.
(b) In this type the legs and toes are very long and slender and the web is absent or feebly developed,
(c) The feet are modified for walking over the aquatic leaves (vegetation) or marshes.
Essay # 9. Palate in Birds:
In general, the skull in various birds does not show much variation. Amongst some of the universal skull characters of birds are- an early ankylosis of bones except in Ratitae, rounded and spacious cranium, single small rounded occipital condyle formed by basioccipal, the upper beak composed mainly by the two premaxillae united into a large triradiate bone, the slender maxillo-jugal arch, the large parasphenoidal rostrum, the freely articulated quadrate and the reptilian post-frontals. Orbits are large, separated by a thin interorbital septum formed by the mesethmoid which is continued anteriorly with cartilaginous internasal septum.
Importance of Palate in Classification:
There are, however, marked differences in the structure of the palatal region of skull in birds which provides an important character for their classification. The living birds are classified in two suborders- Palaeognathae and Neognathae. In the Palaeognathae or Ratitae are included all the flightless birds.
They have a dromaeognathous type of palate in skull in which the large vomer is extended posteriorly, so that the two palatines do not meet with one another and with the rostrum.
On the other hand, in Neognathe or Carinatae are included all the modem flying birds. They have a neognathous type of palate with three subtypes (schizognathous, desmognathous and aegithognathous), in which the vomer is small or absent, so that the palatines meet the rostrum.
Kinds of Palate in Birds:
Huxley, in 1877, pointed out the following four types of palate in birds (Fig. 28.8), based on the relations of vomer, palatines, pterygoids and maxillo-palatine processes.
1. Palaeognathous or Dromaeognathous Palate:
This type of palate is characteristic of Ratitae, such as the ostrich, rhea, kiwi and tinamous, etc.
(i) Vomer is large and broad behind connected with the palatines.
(ii) Palatines do not articulate with the parasphenoidal rostrum, because the vomer intervenes between the two.
(iii) Maxillo-palatine processes are small and do not unite with one another or with the vomer.
(iv) Basipterygoid processes of basis phenoid are well developed and they articulate with the hinder part of the pterygoids.
(v) Pterygoids are immovably fixed to vomer and are reptilian in form.
This type of palate is primitive and occurs in the Palaeognathae.
2. Schizognathous Palate:
This type of palate is common in a variety of birds, such as pigeons, fowls, gulls, plovers, cranes, woodpeckers, trogons, etc.
(i) Vomer is small and pointed in front, or absent.
(ii) Palatines and pterygoids articulate with the parasphenoidal rostrum at the point where they join one another.
(iii) Maxillo-palatine processes do not unite with one another or with the vomer.
(iv) Basipterygoid processes may be absent or small and arising at the base of the rostrum.
(v) Pterygoids are movably articulated.
3. Desmognathous Palate:
This type of palate is common in most of the wading and swimming birds such as storks, herons, ducks and geese, besides parrots, birds of prey, cuckoos, etc.
(i) Vomer is often abortive or so small that it disappears in the skeleton. When present, it is always narrow, slender and tapers to a point in front.
(ii) Palatines and pterygoids articulate with the rostrum.
(iii) Maxillo-palatines are large and united with one another across the middle line, often forming a flat, spongy palate ventral to the vomer.
(iv) Basipterygoid processes are absent.
(v) In parrots, a special type of desmognathous type of sliding palate occurs so that the depression of the lower jaw automatically raises the upper jaw.
4. Aegithognathous Palate:
This is similar to the schizognathous type of palate. It occurs in passerine birds such as crows, swifts, bulbuls, etc. Vomer is short and broad and truncated instead of being pointed in front. Posteriorly the vomer is deeply cleft embracing the rostrum.
Essay # 10. Economic Importance of Birds:
Birds occupy a very significant position in the human society. They provide us food, medicine, fertilizers, beautiful decorative, give us enchanting songs and bring about pollination. In addition, they form various sources of amusement and exercise biological control over injurious crop pests. Besides their many beneficial aspects, certain birds are harmful for mankind.
All sorts of economic significances of birds can be best studied under following headings:
I. Beneficial Birds:
Some of the important beneficial birds to man are as follows:
1. As Food:
Both the flesh and eggs of birds are used as food by man. Certain animals such as snakes, cats, civets, mongoose, etc., also prey upon small birds and their eggs. The flesh of certain birds such as chicks, ducks, geese, praise chickens, pigeons, turkeys and shore birds is much relished and is regarded as delicacy.
Several species of these birds have been domesticated and hybridised by man for many centuries to produce better qualities of feathers, flesh and messengers, etc. Domestic fowl is supposed to be a delicacy and its eggs are considered to be the best standard food, second only to milk. The eggs of fowl are also used in tofees, pastries, cakes and biscuits. The great demand of flesh and eggs of fowl has given rise to the paying poultry industry.
Besides flesh and eggs, even nests of certain birds have food value. For instance, Chinese use the nests of a particular species of swift (e.g., G. collocalia) as food. These are said to have tonic property and are formed purely of salivary secretion.
2. In Medicine:
Feathers and muscles of certain birds are utilised in certain Ayurvedic and Unani medicines. In Unani system, patients of chest diseases and tuberculosis are prescribed to keep pigeons’ bodies in contact with the chest. Flesh of pigeon is said to be good for the patients of paralysis. The eggs of fowl are used in tonics and various medicines. The eggs of fowl have great experimental value, as they are used as a medium to grow cultures of viruses, bacteria, fungi, nematode larvae, etc.
3. Decorative and Commercial Value:
The simple or multicoloured and fastidious feathers of different birds have great economic importance for man. They have been used extensively for pillows, quilts, blankets, clothing and sleeping bags. The down feathers of aquatic birds, such as ducks and geese, provide the warmest insulation and much used for Arctic clothing, ski attire and for sub-zero, sleeping bags.
Feathers with beautiful and distinctive colours and shapes have been used in decoration of houses and ornamentation by native peoples and modern women. Red Indians of America use wing and tail feathers of golden eagles for ceremonial headdresses and feathers of flicker and valley quail for decoration. Domesticated poultry and ostriches, rheas, etc., provide ornamental feathers. Badminton shuttlecocks are manufactured out of feathers.
Many natives use feathers in their arrows so that they may go farther. In Argentina and Brazil, the feathers of rheas are used as feather dusters. In India, the tail feathers of peacocks are used in house decoration, ornamentation and in making a variety of toys, fans, etc. In the Mughal period, the long feathers of birds were used as writing pens.
4. Agricultural Value:
The birds are of great agricultural value since they act as pollinator, fertilizer and help in biological control in the following manner:
(a) As Pollinator:
Many small birds like humming birds, living in grooves and meadows on flowering plants bring about their pollination. Certain flowers are specially designed for bird- pollination and respond to them only. The fruit-eating birds help in the dispersal of seeds far and wide.
(b) As Fertilizer:
The faecal matter of birds contains nitrogen, phosphates, calcium and iron, etc., and is called guano. It is extensively used as fertilizer. On islands of the coast of Chile, where little rains fall, and which are breeding places of numerous migratory and sea-birds, the guano accumulates in enormous quantities and is exported to different countries.
(c) In Biological Control:
Birds prove one of the best friends of farmers as they exercise biological control over injurious crop pests. The seed-eating birds control the harmful weeds of agricultural fields by consuming thousands of tons of weed seeds annually. Likewise, the insectivorous birds devour millions of tons of harmful insects which live as pests on the crop plants.
Certain carnivorous birds such as owls, eagles and hawks prey upon mice, rats, moles, squirrels, hares, rabbits and other rodents and, thus, protect the crops from damage. Birds also pick up larvae of insects which devour the plant leaves and also feed up worms of harmful nature.
5. As Scavengers:
Carrion-eating (scavenger) birds, like vultures, hawks, eagles and crows, etc., are of great sanitary value, as they feed upon the dead bodies and decaying organic substances. These birds check the spreading of such diseases, which might be caused due to decay and putrefaction of dead bodies. Certain other scavengers like cattle-egrets, ox-peckers, rhinoceros-bird, African starlings and crocodile birds, etc., remove parasites from the wild animals on which they live.
6. Miscellaneous Value:
Besides above described values, birds have following uses for man:
(i) As Predators:
Certain birds such as peacocks, eagles, kites and other carnivorous birds are destroyers of several venomous and injurious creatures, such as snakes, scorpions, etc.
(ii) As Messengers:
Some species and varieties of pigeons have been trained and used as messengers in wars and love affairs from early days.
(iii) As Signals:
Many birds profess changes in seasons. In India, the appearance of cuckoo suggests the onset of spring. The dance and peculiar voice of peacocks in cloudy weather indicate rainfall. Certain birds help hunters by giving danger signals to them. Some sparrows cry before carnivorous animals such as tigers hidden in the bushes. A typical path sparrow cries along the path of king cobra.
(iv) Entertainment Value:
Game birds like ducks, quails, herons, pheasants, etc., are used for entertainment. These birds are hunted by persons as a recreation.
(v) Singer birds like cuckoo, bulbuls and canary amuse persons by their sweet and melodious voice.
(vi) Parrots, Mynas, and Parakeets amuse man by repeating their voices and are, thus, good sources of recreation and so they are kept in cages and aviaries as pets. Pigeons, cocks and partridges are tamed for play. Parrots are used by the roadside astrologers.
II. Injurious Birds:
In spite of their great positive economic values, birds are not all beneficial to mankind. Many birds, in fact, cause tremendous damage to mankind.
Some of the injurious acts of birds are the following:
1. Menace to Agriculture:
Some birds damage crops in various ways. They feed upon newly planted seeds, young seedlings, destroy leaves and flowers and spoil fruits and seeds. In Malva, crows do great damage to groundnut crops by eating groundnuts. In Australia sparrows have become serious crop pests. In India, sparrows, parrots, etc., do great harm to agriculturists and horticulturists. As parrots destroy fruits either ripe or unripe, sparrows destroy granaries. Further, the insectivorous birds may feed on beneficial insects and worms along with injurious ones.
2. Destroyer of Game Birds:
The hawks, owls, etc., cause great damage to poultry yards by preying upon young chickens. They also attack upon the game birds and kill them. Nestor notabilis (New Zealand parrot) dig out the kidneys and fat of sick and weak sheep.
3. Damage to Fisheries:
Certain fish-eating birds such as herons, etc., feed upon fishes and cause great damage to fish industry.
4. Carriers of Diseases:
Many birds act as carriers to large number of harmful larval stages and transmit them to their new hosts. They also spread the noxious germs of various fatal diseases by feeding upon infected insects and worms and depositing their excreta in human food.
5. Pests of Honey Bees:
Birds destroy and feed upon honey bees and their nests. Certain birds (honey-guides) attack on the nests of honey bees by the cooperation of little badger and feed upon their grubs and on themselves, while badger feeds upon the honey. Badger has a sting- proof hide and coat of coarse hairs and, hence, it is protected from the stings of bees.
Whatever might be the injurious effect of birds to man, their uses overweigh them and, hence, it can be safely concluded that birds are the best companions of mankind.