Sexual Suicide by Honeybees

Sexual Suicide by Honeybees

Introduction 

The male honeybee, called a drone, exists for one reason and one reason only: to mate with a virgin queen. He is entirely expendable after he provides this service to the colony. The drone takes his mission seriously, however, and gives his life for the cause. 

How Honeybees Do the Deed

Honeybee sex occurs in mid-air when the queen flies out in search of mates, her one and only "nuptial flight." Drones compete for the chance to mate with their queen, swarming around her as she flies. Eventually, a brave drone will make his move.

As the drone grasps the queen, he everts his endophallus using a contraction of his abdominal muscles and hemostatic pressure and inserts it tightly into the queen's reproductive tract. 

He immediately ejaculates with such explosive force that the tip of his endophallus is left behind inside the queen and his abdomen ruptures. The drone falls to the ground, where he dies soon after. The next drone removes the previous drone's endophallus and inserts his, mates, and then dies as well.  

Queen Bees Really Get Around

During her one nuptial flight, the queen will mate with a dozen or more partners, leaving a trail of dead drones in her wake. Any drones that remain around the hive in the fall will be unceremoniously driven from the colony before cold weather sets in. 

Honey stores are simply too precious to waste on a sperm donor. The queen, on the other hand, will store the sperm for use throughout her life. The queen can store 6 million sperm and keep them viable for up to seven years, with the potential of producing 1.7 million offspring during her lifetime, as she uses a few at a time to fertilize her eggs.

Bee Egg Development

In late winter, the queen then lays eggs in the cells of the hive, up to 1,000 in one day at the height of the season. The hive needs mature bees to be ready to go when flowers with pollen are emerging, but she will continue to lay eggs until fall. 

Worker bee eggs mature in about 21 days, drones in about 24 days (from unfertilized eggs), and other queens in about 16 days. The hive needs backup queens in case the queen dies, becomes incapable of laying eggs or is lost because a hive doesn't survive without one. 

What Workers Do

In contrast to the drones, female worker bees take on many jobs. They clean cells for eggs to be laid; feed larvae; construct the comb; guard the hive; and forage. They can lay an egg to become a drone if needed, but their eggs can't become workers or queens.

Class Mammalia

Class Mammalia

Introduction

Animals belonging to class Mammalia are referred to as mammals. Mammals are one of the most evolved species in the animal kingdom categorized under vertebrata.

They exhibit advanced characteristics which set them apart from all other animals. They are characterized by the presence of mammary glands through which they feed their younger ones.

They are distributed worldwide and have adapted well to their surroundings – from oceans, deserts and polar regions to rainforests and rivers etc.

Let us have a detailed look at the characteristics and classifications of the animals belonging to the class Mammalia.

Characteristics Of Mammals

Following are a list of distinct characteristics of mammals that separates them from other classes:

1.Mammals are warm-blooded animals who give birth to their younger ones.

2.They are the most dominant form of animals found in almost all types of habitats.

3.They have mammary glands that help them produce milk to feed their younger ones

4.Presence of region of the brain known as Neocortex

5.Their skin possesses oil glands (sebaceous glands) and sweat glands (sudoriferous glands).

6.The fur of hair throughout the body which helps animals adapt to their environment.

7.They are heterodont, i.e., possess different types of teeth.

8.Mammals also possess cervical vertebrae.

9.The skull is dicondylic.

10.The trunk is divided into thorax and abdomen.

11.The mammals respire through lungs.

12.Good sense of hearing as mammals are aided with 3 middle ear bones

13.Mammals have a four-chambered heart. The sinus venous and renal portal system are absent.

14.Presence of single-boned lower jaws.

15.The brain is well developed divided into cerebrum, cerebellum and medulla.

16.They possess 12 pairs of cranial nerves.

17.Exhibit one of the most advanced forms of Diaphragms.

18.The mammals can lay eggs also. They are known as viviparous.

Classification Of Mammals

Mammalia has the largest class in the animal kingdom. Based on their reproduction, they are classified into three subclasses:

Prototheria

Metatheria

Eutheria

Prototheria

Also known as Monotremes, the sub-class Prototheria consists of egg-laying mammals. It has one order having 6 species

Order: Monotremata

Example: Duckbilled platypus, Echidna.

Metatheria

Mammals belonging to this sub-class give birth to immature young ones, hence they stay in their mother’s pouch until they mature. For eg., Marsupials and Kangaroos. They are divided into seven different orders:

Order - Examples

Notoryctemorphia - Marsupial modes

Diprotodontia - Kangaroo

Microbiotheria - Colocolo

Didelphimorphia - New world opossum

Dasyuromorphia - Dasyurids

Peramelemorphia - Bandicoots

Paucituberculata - South American rat opossum

Eutheria

Mammals under this subclass give birth to young ones. The young ones are developed inside the mother and derive nutrition through the placenta from the mother. Furthermore, it consists of 19 orders, few of which are:

Order - Examples

Proboscidea - Elephants

Rodentia - Rats

Artiodactyla - Cows

General Classification of Mammals

The scientists have also classified the mammals on a general basis which makes it easy to learn about the mammals and their distinguishing characteristics.

Classification - Examples

Animals - Lion, Tiger, Dog

Marsupials - Kangaroo, Koala, Womba

Primates - Chimpanzee, Gorilla, Monkey

Rodents - Squirrel. Mouse, Porcupine

Cetaceans - Dolphins, Whales

Other mammals - Seal, Walrus, Sea-lion

Platypus (Duck-billed Platypus) 

Classification 

Scientific name: Ornithorhynchus anatinus

Kingdom     : Animalia

Phylum        : Chordata

Subphylum : Vertebrata

Class           : Mammalia

Subclass     : Prototheria 

Order           : Monotremata 

Family         : Ornithorhynchidae 

Genus         : Ornithorhynchus 

Specie        : O. anatinus 

The Platypus is a unique Australian species. Along with echidnas, Platypuses are grouped in a separate order of mammals known as monotremes, which are distinguished from all other mammals because they lay eggs. When first discovered, the unusual look of a Platypus caused considerable confusion and doubt amongst European naturalists and scientists, many of whom believed that the animal was a fake.

Identification

Platypus is well adapted for semi-aquatic lifestyle. Its streamline body and a broad, flat tail are covered with dense waterproof fur, which provides excellent thermal insulation. The Platypus propels itself through the water by using its front, short, webbed limbs, and the partially-webbed hind feet act as rudders. 

Behind its distinctive bill are the grooves that house the ear openings and the eyes which close when the animal dives. The Platypus uses its tail for storage of fat reserves and the strong claws on its feet for burrowing and moving on land. 

In addition, males possess a horny spur on their ankles, which is connected to a venom gland in the upper leg, making the Platypus one of the few venomous mammals.

The skeleton of the Platypus is heavy and has several similarities to that of fossil and modern reptiles. These include pectoral girdles made of five bones, splayed legs and rudimentary ribs on the neck vertebrae.

Distinguishing features of a Platypus are: streamlined body with a bill and broad flat tail; short limbs with webbed feet; dense dark brown to reddish brown fur with light brown/silver underfur.

Habitat

Platypuses occur in freshwater systems from tropical rainforest lowlands and plateaus of far northern Queensland to cold, high altitudes of Tasmania and the Australian Alps. 

They feed in both slow-moving and rapid (riffle) parts of streams, but show preference to coarser bottom substrates, particularly cobbles and gravel. When not foraging, the Platypus spends most of the time in its burrow in the bank of the river, creek or a pond. 

At times, the individuals use rocky crevices and stream debris as shelters, or they burrow under the roots of vegetation near the stream. Hence, the ideal habitat for the species includes a river or a stream with earth banks and native vegetation that provides shading of the stream and cover near the bank. 

The presence of logs, twigs, and roots, as well as cobbled or gravel water substrate result in increased microinvertebrate fauna (a main food source), and the Platypus also tends to be more abundant in areas with pool-riffle sequences.

Distribution

Platypus is endemic to Australia and is dependent on rivers, streams and bodies of freshwater. It is present in eastern Queensland and New South Wales, eastern, central and southwestern Victoria and throughout Tasmania. 

The western limits of the range are poorly known. The species was once found in the Adelaide Hills and Mount Lofty Ranges of South Australia. Nowadays it is extinct from that state, except for the introduced population on the western end of Kangaroo Island. 

There is no evidence that the animal occurred naturally in Western Australia, despite several unsuccessful attempts to introduce it there. Within its current distribution, the occurrence of the Platypus is reasonably continuous in some, but discontinuous in other catchments.

Seasonality

Platypuses are active all year round, but mostly during twilight and in the night. During day, individuals shelter in a short burrow in bank. The activity patterns of these animals are determined by a number of factors including: locality, human activity, ambient temperatures, day length and food availability.

Feeding and diet

The Platypus feeds mainly during the night on a wide variety of aquatic invertebrates. The average foraging periods last for 10-12 hours per day, and the distances the animals move during this time vary between individuals and their distribution. 

The animal closes its eyes, ears and nostrils when foraging underwater and its primary sense organ is the bill, equipped with receptors sensitive to pressure, and with electro-receptors. The precise way in which the Platypus uses the bill to detect prey is still unknown, but the bill serves to find and sift small prey from the substrate, while larger prey is taken individually. 

The Platypus stays underwater for between 30-140 seconds, collecting the invertebrates from the river bottom and storing them in its cheek-pouches. It then chews the food using its horny, grinding plates, while it floats and rests on the water surface.

Diet of the Platypus consists mainly of the benthic invertebrates, particularly the insect larvae. The species also feeds on free-swimming organisms: shrimps, swimming beetles, water bugs and tadpoles, and at times worms, freshwater pea mussels and snails. Occasionally the animals catch cicadas and moths from the water surface. In captivity, the Platypuses are often fed freshwater crayfish (Yabbies).

Other behaviours and adaptations

When swimming, the Platypus presents a low profile, with three small humps (the head, back and tail) visible above the water surface. The swimming action is smooth, and when the Platypus dives the back is arched as the animal plunges underwater, creating a spreading ring. These characteristics coupled with the absence of visible ears distinguish the Platypus from the dog-paddle style of the Water-rat.

Platypuses can swim through fast waters at the speed of around 1 metre per second, but when foraging the speed is closer to 0.4 metres per second. However, the Platpus is not well adapted for walking on land. The limbs are short, heavy and splayed away from the body, and a Platypus uses almost 30% more energy when moving on land, compared to a terrestrial mammal of similar size.

Communication

The Platypus is largely a solitary animal, but several individuals can share the same body of water. The vocalisation has not been recorded in the wild, but captive animals produce a low-pitched growling sounds when disturbed or handled.

Life history cycle

Young Platypuses do not seem to reproduce in their first year of life, instead, both sexes become reproductive in their second year. Still, many females do not breed until they are at least 4 years old. 

After mating, a female will lay 1-3 eggs (usually 2) following a 21-days gestation period. She then incubates the eggs for possibly 10 days, after which the lactation period lasts for 3-4 months before the young emerge from the burrow. Platypuses are long-lived animals both in captivity and in the wild, living up to approximately 20 years.

Breeding behaviours

The breeding season of the Platypus varies with distribution and within populations. Studies suggest that breeding occurs earliest in Queensland, followed by New South Wales, Victoria and Tasmania. Mating normally takes place between August to October in New South Wales and Victoria, and lactating females were observed between September and March.

The knowledge of the breeding behaviour generally comes from observations of animals in captivity. In winter (when the water is still cold) males initiate mating interactions. Courtship includes aquatic activities such as: rolling sideways together, diving, touching and passing, and the male is also observed grasping a female’s tail with its bill. The behaviour last from less than a minute to over half an hour and is usually repeated over several days.

After mating, a pregnant female builds a nest in a long complex burrow (possibly re-worked by several females in different seasons) in less than a week. She spends further 4-5 days collecting wet nesting material to prevent her eggs and hatchlings from drying out. During the egg incubation period, a female holds the eggs pressed by her tail to her belly, while curled up. 

She intermittently leaves the burrow, however, much of this aspect of the animal’s life is still unknown. When the young hatch, the female starts secreting milk and the young Platypuses suckle from the two milk patches covered by fur on the female’s abdomen. 

The female spends most of this time with her young in the burrow, and as the young grow, she increasingly leaves them to forage. Towards the end of the summer the young emerge from the burrow and their fate as young independent animals is still largely unknown.

Conservation status

The Platypus is protected by legislation in all of the states that it occurs in. Individuals cannot be captured or killed, except for scientific research. The Platypus is a common species with very little apparent change in its historical distribution (except in South Australia). However, there is a general lack of knowledge in the species abundance at local catchment levels to predict population trends. The dependence of Platypuses on the established freshwater systems may lead to their decline in future.

Under IUCN the Platypus has been listed as Near Threatened species (year assessed 2014).

Predators

Platypuses spend most of their time in water or their burrow, so it is difficult to determine their predators. There have been anecdotal reports of the species being predated on by crocodiles, goannas, carpet pythons, eagles and large native fish. In addition, it is likely that foxes, and possibly dogs or dingoes kill Platypuses that move on land or in shallow waters.

Platypuses have a number of ectoparasites in the wild, including their own tick species, Ixodes ornithothynchi. The tick is often found around the hind limbs, and in smaller numbers on the front legs and in the body fur. Severe skin ulcers caused by the amphibian fungal infection have been reported in Tasmanian Platypuses in particular. The fungus can be fatal to the animal if it invades other tissues, particularly the lungs.

Danger to humans

Male Platypuses have a calcaneous, sharp spur about 12 millimetres long on each ankle. The spur is connected via a long duct to a gland that produces venom, particularly in the breeding season. The venom can cause severe pain to humans, and although not lethal, the pain caused has been described as excruciating. 

Swelling rapidly develops around the wound and gradually spreads throughout the affected limb. Information obtained from case histories and anecdotal evidence indicates that the pain develops into a long-lasting hyperalgesia (temporary increased sensitivity to pain) that persists for days or even months. Therefore, if there is a need to handle a Platypus (helping an injured animal for instance), it should always be picked up by the end half of the tail to avoid the spur in case it is a male.

Fossils description

The fossil record for monotremes is poor in comparison to that of other groups of mammals, and until recently little was known about their evolutionary history. Several fossil discoveries since the early 1970s have shed some light on the origins of monotremes. 

We now know that monotremes were present in Australia during the Mesozoic Era, when Australia was still part of the supercontinent, Gondwana. The fossil evidence suggests that monotremes originated and diversified in the Australian/Antarctic section of Gondwana, and that there was only a single dispersal to South America before the break up of Gondwana.

Four species related to Platypus have been found in fossil deposits from Australia, including a complete skull of Obdurodon dicksoni and an opalised jaw fragment of Steropodon galmani. The latter is 110 million years old and represents one of Australia's oldest mammals. The only evidence that Platypus ancestors were once present outside Australia came in 1991, when a 61-63 million year old fossil tooth was found in Patagonia, in southern Argentina.

Studies of these fossils indicate that the one remaining living species of Platypus is more specialised than its predecessors. It is smaller, its functional teeth have been replaced by horny pads and other aspects of its anatomy appear simpler. It also appears to have a more restricted distribution, being confined to the river systems of eastern Australia. Although Platypus remains widespread and reasonably common, this trend towards increasing specialisation suggests that it may be moving out onto an evolutionary 'limb' and that its current status should not be taken for granted.

Hornbill (Bucerotidae)

Hornbill (Bucerotidae)

Introduction 

Hornbill is a bird species and falls under any of the sixty species of the Old-World tropical birds of order Coraciiformes. The scientific name of hornbill is ‘Bucerotidae’, which means ‘cow horn’ in Greek. They are specifically noted for their characteristic feature of a bony casque which is crowned on their prominent bill. This is found only in a few species. They are found to have a large head that is held by a thin neck. Their wings are broad and their tails are long. The plumage is usually black or brown, having bold white markings. The size of hornbills ranges approximately from 16 inches (i.e., 40 cm) to 63 inches (i.e., 160 cm). The Tockus species is generally smaller in size than that of the great hornbills. Several hornbill species like the Rhinoceros hornbills have the preen gland near the base of their tail. When the beak and the casque rub against this gland, an oily, reddish-orange fluid is secreted which gives the beak and casque a bright, reddish tone.

Classification 

Kingdom      : Animalia

Phylum         : Chordata

Subphylum  : Vertebrata 

Class            : Aves

Order            : Coraciiformes

Suborder      : Bucerotes

Family           : Hornbills (Bucerotidae)

Number of genera, species - 14 genera; 54 species.

Habitat - Forest, woodlands, and savanna.

Conservation status - Endangered: 2 species; Critically Endangered: 2 species; Vulnerable: 5 species; Near Threatened: 12 species.

Physical characteristics

Hornbills are among the most flamboyant birds of their habitat. The oversized, slightly decurved bills topped by sometimes outlandish casques shaped as bumps, ridges, or horns make hornbills an unforgettable component of any landscape. 

Hornbills vary tremendously in size and shape, starting with the large, long-legged southern ground-hornbill (Bucorvus leadbeateri) weighing up to 13.2 lb (6 kg), and going down to the 0.26 lb (120 g) red-billed dwarf hornbill (Tockus camurus). 

Males are always larger and stouter than females but the greatest dimorphism often occurs in bill length with males having up to 30% longer bills. Horn-bill plumage is described as "drab," lacking the brilliant colors of relatives such as the kingfishers (Alcedinidae) and rollers (Coraciidae). 

However, the bold black-and-white patterns of many forest hornbills and the delicate gray pied patterns of many Tockus species are far from dull. Add in bills and casques of brilliant orange, yellow-gold, deep crimson, or shiny black, and patches of bare skin around the eyes and throat in a kaleidoscope of garish hues, and you have a colorful group of birds.

Plumage color and size and shape of the casque identify the age and sex of an individual. Newly fledged hornbills have underdeveloped casques and small bills, but after the first year of life, appearances converge on that of their adult counterparts. 

In species where sexes differ in color as adults, determining the gender of the young can be difficult. For example, in almost all Aceros, Rhyticeros, Penelopides, and Tockus species, the young, regardless of their sex, resemble their fathers for the first year of life. 

The opposite is true for the Bycanistes and Ceratogymna who resemble the adult female. Young of the northern ground-hornbill (Bucorvus abyssinicus) and a few Tockus species show plumage true to their sex while chicks of the rufous hornbill (Buceros hydrocorax) are radically different from both parents.

Numerous authors have described the noise produced by flying hornbills as that of an approaching train. This incredible "whooshing," produced in different pitches depending on the species' size, is a result of wing structure. 

Because horn-bills lack the small feathers that normally cover the shafts of the primary and second flight feathers, each powerful stroke of the wing allows air to pass through and vibrate the large feathers.

The most outstanding feature, and the one from which hornbills acquire their common name, is the casque on the top of the bill. Casques vary from the mere ridge of the redbilled hornbill (Tockus erythrorhynchus) to the wash-board bumps of the wreathed hornbill (Rhyticeros undulatus) and the elaborate banana of the rhinoceros hornbill (Buceros rhinoceros). 

The function of casques, which may take up to six years to develop, is the topic of many debates. It is possible that casques provide structural support for a long bill. Casques may also serve an acoustic function by helping amplify a horn-bill's call. Additionally, casques may be attractive to the opposite sex. 

The helmeted hornbill uses its casque in bizarre, aerial displays where individuals of either sex collide in midair, casque-to-casque. The head-butting competitions always occur near fruiting fig trees (Ficus spp.). 

Although Gustav Schneider once reported that helmeted hornbills perform this comical ritual when they are intoxicated on fermented figs, observations from Sumatra indicate that this acrobatic act may be in defense of clumped food resources.

Behavior

Hornbills generally wake at dawn, preen their feathers, then begin their search for food. Normally, hornbills move about in pairs, but some species are found in family groups of three to 20 individuals. Some hornbills gather in large flocks around clumped food resources. 

The Sulawesi redknobbed hornbill is occasionally seen in groups of more than 100 individuals at large fruiting figs. In Thailand, wreathed hornbills roost in flocks of over 1,000 individuals. The plain-pouched hornbill (Aceros subruficollis) takes the record for the largest aggregations; over 2,400 individuals were counted in Malaysia in 1998 traveling to roost. 

Roosts may serve as "information centers" where individual birds can reduce foraging time by following a knowledgeable, long-term resident. As Alan Kemp summarizes, these massive gatherings are "wonderfully noisy and visually stunning, and must surely rate among the foremost spectacles of the bird world."

Hornbills are believed to be monogamous. The only research on the faithfulness of hornbills failed to find evidence of extra-pair paternity in Monteiro's hornbill (Tockus monteiri), boosting confidence in their monogamous behavior. 

Monogamy may have many variations on the theme. Among cooperative social groups, there is generally one monogamous breeding pair and a number of offspring who become "helpers" during the nesting season, delivering morsels to their mother and siblings and defending a mutual territory. 

Cooperative breeding occurs more often in hornbills than any other bird family, and may characterize up to one-third of all hornbill species.

Many hornbills range widely but none of these movements is considered migratory. Most hornbills are sedentary and many are territorial. The majority of Tockus and small-bodied forest hornbills are territorial throughout the year. 

Larger hornbills such as the Aceros and Rhyticeros that rely on scattered fruit resources, may range over 21 mi2 (58 km2) and only defend temporary territories around nest sites.

Hornbills communicate through a wide range of spectacular calls and each species can be identified by its vocalizations. Loud calls announce territories, or in the non-territorial species, aid in maintaining contact. 

Territorial ground-hornbills "boom" when their boundaries are invaded and non-territorial wreathed hornbills bark like dogs while coordinating flocks. While calls are important in dense forest habitats, visual displays are more prevalent in open grasslands. 

For example, the Hemprich's hornbill (Tockus hemprichii) has an elaborate territorial display that resembles the mechanical movements of a wind-up toy; the bill is pointed skyward, while the bird whistles, and lifts and fans its tail over its back.

Feeding ecology and diet

Hornbill diets span the spectrum from animals to fruits and seeds but most are omnivorous, mixing meat and fruit in their meals. 

Among Tockus, diets tend more toward insects, scorpions, lizards, snakes, and small mammals, while Ocyceros and tarictic diets include more fruit. Omnivory is the rule among the territorial, group-living hornbills. 

Because animal prey often occurs at low density and is available year-round, hornbills may develop defendable territories in which dietary needs for the pair or group are satisfied. 

Additionally, these species maximize exploitation of their territories by using abundant but ephemeral fruit resources as they become available. The availability of fruit resources within a habitat may determine the degree of omnivory observed.

Heavy reliance on fruits requires that hornbills have large home ranges, and may affect reproductive rates. Fruit diets combined with large home ranges have important consequences for forest ecology. 

As hornbills travel, they disperse seeds of the fruits they relish, playing a role in regenerating the forests in which they live.

Reproductive biology

Hornbill reproduction tends to coincide with rainfall and increased food supply. In seasonal African savannas, Tockus species begin courtship and reproduction with the rains, when invertebrates and fruits are plentiful. 

The opposite occurs on Sulawesi where lack of rainfall stimulates reproduction in the Sulawesi red-knobbed hornbill, so the burst in fruit supply occurs immediately after fledging. 

In aseasonal Bornean rain-forests, reproduction appears to be supra annual, tied to highly cyclical peaks in food supply. 

Breeding in these populations may be controlled by the rate at which pairs regain condition between reproductive cycles. In fig-rich forests of North Sulawesi, hornbills breed every year, usually returning to the same nest tree.

The hornbill's unique nesting behavior is the feature that has most fascinated students of nature. All hornbills are hole-nesters, preferring natural cavities in trees or rock crevices. 

Unlike any other group of birds, the female hornbill seals the entrance to her nest cavity, leaving only a narrow slit through which she, and later her chicks, receive food from her mate. 

In most species, the male ferries mud to the female who then works for several days to seal the cavity entrance. Where mud is a rare commodity, the female uses her own feces as building material.

Nest sealing is believed to have evolved as a form of predator defense, for protection against other intruding hornbills, and to enforce male fidelity. Nest sealing has been described as an example of male chauvinism in which the male cloisters his female, forcing her to depend on him for survival. 

In reality, the female incarcerates herself and later frees herself, forcing the male to provide for her and their offspring. Because the male is busy provisioning his family, he is incapable of maintaining two nests, and the female can be sure of his complete attention.

The onset of breeding begins with courtship. When in flight, courting pairs act as though they are attached by an invisible rubber band, reacting swiftly to each other's movements. 

They perch in cozy proximity, engage in mutual preening, and exchange food gifts as a demonstration of their ardor. 

Other clues of the onset of breeding include the intensification in color of the exposed fleshy areas around the face and throat, reflecting hormonal changes. Nest inspection increases in frequency until copulation occurs and the female enters the nest cavity.

The number of eggs, their size, and the length of incubation are all correlated with body size. Clutch size ranges from two to three eggs in large hornbills and up to eight for smaller hornbills. 

Incubation runs from 23-49 days in small and large species, respectively. Eggs hatch in intervals and the emerging chicks are naked and translucent pink with closed eyes. Feather growth begins within a few days and as chicks develop, the skin blackens and begging calls change from feeble cheeps to loud, insistent calls.

The timing of female emergence varies tremendously; some females accompany their chicks from the nests and others leave well before chicks fledge. Research on Monteiro's hornbill suggests that females emerge to ensure survival when their body condition reaches its lowest point.

Male hornbills can be impressive providers. Although many Tockus species carry items to the nest one-by-one, most hornbills collect multiple food items, stuffed into a bulging gullet before delivering a load to the nest. A Sulawesi redknobbed hornbill once delivered 162 fruits in one trip, a load equivalent to nearly 20% of his body weight.

Nesting success is high for those species studied. In southern Africa, chicks fledged from 90–92% of the nests of four Tockus species and in Thailand, 80% of great hornbill nests monitored fledged young. Sulawesi red-knobbed hornbills averaged 80% nesting success over three years, but this figure plummeted to 62% during the 1997 El Niño/ENSO fires. Smaller hornbills fledge up to four chicks, but large hornbills rarely fledge more than one chick per year.

Conclusion

The hornbills are noted by the International Union for Conservation of Nature (IUNC) Red List of Threatened Species so that the majority is not on the verge of getting extinct. Species of hornbills like the bushy-crested hornbill (Anorrhinus galeritus) in South Asia and the crowned hornbill (T. alboterminatus) in southern Africa are extended in huge geographic ranges due to their large populations. However, due to hunting pressure and deforestation, ecologists found that the population of some species is under threat. The IUNC Red List classifies some species to be endangered which include the Narcondam hornbill, the Visayan hornbill (P. panini), a native to Panay Island and its small, neighbour islands, and the Mindoro hornbill (Penelopides mindorensis), which is from Mindoro in the Philippines. Also, the rufous-headed hornbill (Aceros waldeni), also known as Walden’s hornbill, and the Sulu hornbill (Anthracoceros montani) are listed to be critically endangered. Both the helmeted hornbill and the great hornbill are protected due to their casque, which is used as carving material like ivory.

Facts

1.The Rhinoceros Hornbill is the mascot of Sarawak city. But, other hornbills are also found here and for obvious reasons, the nickname ‘the land of hornbills’, is given.

2.Hornbills are the best friends of monkeys as these birds eat up the insects which annoy the monkeys. In return, the hornbills get warning calls from the monkeys if they see any humans.

3.The calls made by hornbills are very loud and distinct. The Indian great hornbills make a roaring sound, the Von der Decken’s hornbills make a clucking sound, and the southern ground hornbills make a resounding bass sound.

4.During the nesting period, the male bird can carry up to sixty fruits in a single go. They also flap their wings on the nest to communicate with the female. The flapping action creates a sound similar to a steam engine.

5.Besides constructing nests, the hornbills use their beaks to climb trees also.

Class Aves

Class Aves 

Introduction

The Aves belong to the phylum Chordata of the animal kingdom. It has about 9,000 species. Aves are adapted to fly. All the birds come in the class Aves. They show courtship, parental care, nest building, and territorial behaviour.

Characteristics of Aves

Birds are warm-blooded animals.

Their forelimbs are modified into wings.

They have well-developed flight muscles that help during the flight.

Their hind limbs are adapted for walking, hopping, perching, grasping, wading and swimming.

There are epidermal scales on their legs.

The endoskeleton is bony with long hollow bones filled with air cavities. known as pneumatic bones.

Their spindle-shaped body minimizes resistance of the wind.

The feathers help in preventing heat loss and reduce air friction by providing passage to the air.

There is no skin gland except the oil gland.

The lower and upper and jaws are modified into a beak.

They have no teeth.

They have sharp eyesight.

The alimentary canal has a crop and a gizzard. The crops help in softening food, and the gizzard helps in crushing the food.

Pigeons and other seed-eating birds lack a gall bladder.

They have spongy and elastic lungs for respiration.

The special vocal organ called syrinx is present at the base of trachea.

Their heart is four-chambered.

RBCs are oval, nucleated and biconvex.

12 pairs of cranial nerves are present.

They have a single ovary and oviduct on the left side.

All the birds are oviparous and exhibit sexual dimorphism. The eggs have four embryonic membranes- amnion, chorion, allantois, and yolk sac.

Classification of Class Aves 

About 8,600 species of birds are arranged under two subclasses—Archaeornithes and Neornithes:

Subclass Archiornithes:

Mesozoic ancestral or lizard birds with long tail and teeth in both the jaws.

Order Archaeopterygiformes:

So far two genera have been described, each with a single species from the upper Jurassic lime stones of Solenhofen in Bavaria.

1.Forelimbs bear remiges.

2. Tail long with many vertebrae, which gradually taper to the distal end. The rec­trices are arranged in two lateral rows on each side of the caudal vertebrae.

3. The carpals and metacarpals free and hand with three clawed digits.

4. The eyes were large.

5. The skull proportionately large, with a rounded bird-like brain case and strong jaws, in each of which hearing a series of conical teeth lodged in socket.

6. Enamelled crowned teeth on both the jaws.

7. The sacrum made up of only about six vertebrae.

8. The cervical and thoracic ribs probably devoid of uncinates. Thin abdominal ribs or gastralia or so-called ventral ribs were on ventral wall of abdomen.

9. The cerebral hemispheres smooth, long and narrow and cerebellum small.

Examples: Archaeopteryx lithographica, Archaeornis siemensi.

Subclass Neornithes:

These birds first appeared in Cretaceous period and includes few extinct and all other birds known up to date.

1. Tail greatly shortened usually ending in a pygostyle, around which the rectrices, when present, are arranged in a semicircle.

2. Except a few extinct forms all are without teeth.

3. The sternum is well-developed and usually keeled or carinate.

The neornithine birds are arranged in four superorders—Odontognathae, Palaeognathae, Impennae and Neognathae:

Superorder Odontognathae:

New World toothed birds found in Upper Cretaceous period.

1. Clavicle not fused. Sternum without keel. Wing of vestigeal humerus only.

2. Both the jaws were with teeth.

3. Flightless, specialised for swimming, about 150 cm in length.

Order 1. Hesperornithiformes:

1. Flightless, about 90 cm, adapted for swimming.

2. Forelimbs with vestigeal humerus only.

3. The hind limbs laterally directed with webbed feet.

4. The pygostyle absent.

5. Teeth pointed, arranged in grooves in both the jaws, Premaxilla without teeth.

6. The quadrate single, basipterygoid pro­cess absent.

7. Sternum without keel.

8. Long neck provided with heterocoelous vertebrae.

9. Pectoral girdle much reduced, and clavicles not fused.

Examples: Hesperornis, Hargeria, Neogaeornis, Baptornis, Enaliornis, etc.

Order 2. Ichthyornithiformes:

Small marine flying birds, of Upper Cre­taceous of North America.

1. The neck vertebrae amphicoelous.

2. The sternum had a well-developed keel, and the wings were unlike modern birds.

3. Clavicles fused.

Examples: Ichthyomis, Apatormis, etc. Superorder Palaeognathae

Large-sized flightless birds, descended from Volant ancestors at the end of the Mesozoic period.

1. The feathers are primitive, without hooked barbules. Barbs remain free. Apterae are usually absent in adult. The rectrices are absent or irregularly arranged.

2. The wings reduced in size or vestigeal or absent.

3. Pygostyle small or undeveloped.

4. The sternum is flat, raft-like. The coracoid and scapula are comparatively small and completely ankylosed.

5. The coracoscapular angle approaches to right angle and the acrocoracoid process is vestigeal.

6. Large basipterygoid process developed from the basisphenoid. The vomer is large and broad and separates the palatines; which do not come in contact with the cranium.

7. The quadrate articulates with the skull by a single or partially divided facets.

8. The males are with erectile penis and the females have clitoris. The young are precocious.

The superorder has seven orders of which two are extinct.

Order 1. Struthioniforms:

1. Largest existing running birds of Africa and Arabia, about 210 cm tall, 170 kilogram in weight, inhabit arid lands in flocks of 3 to 20.

2. Flightless, terrestrial omnivores with small wings, usually kept folded during running but may be expanded to act as a steering.

3. Head, neck and leg sparsely feathered.

4. Feathers are without after shaft. Tail feathers are replaced by tail coverts.

5. Hind limbs are strongly built and only 2 toes (3rd and 4th) in each foot are present

6. The sternum lacks keel.

7. Pubic symphysis present. Pygostyle absent.

8. At nesting, a male defends 4 to 5 females laying up to 30 eggs in a single nest.

Example: Struthio camelo.

Order 2. Rheiformes:

1. Large flightless running birds of South America, live in groups, about 120 cm tall, feeding on vegetation to insects.

2. Each foot with 3 front toes, webbed at the base.

3. Sternum un-keeled.

4. At nesting a male defends 3-7 females, digs nest and all females lay about 50 lemon-yellow eggs in the same nest ; male incubate them for about 40 days.

Examples: Rhea Americana, Pteronemia pennata.

Order 3. Casuariiformes:

1. The emus and cassowaries of Austra­lia, Papua New Guinea, and East Indies.

2. Flightless, terrestrial, running herbi­vore birds with comparatively small wings supported by a single digit.

3. The neck and body densely feathered. Feathers with after shaft nearly equal to shaft.

4. The plain and savannah-dwelling emus are nearly 180 cm tall with incomplete lining of feathers on neck; inner one of the three toes is a defensive structure, provided with claw.

5. Emu is monogamous. The male digs nest. Female lays 15 or more green eggs. The male incubates first brood while the female incubates the 2nd brood of eggs for about 60 days.

6. The fruit-eating nocturnal cassowaries are confined to the dense tropical rain for­ests; over 150 cm tall with bare skin on head and neck and with a helmet-like horny casque on head which may help in advanc­ing through dense forest.

Examples: Dromaeus (Emu), Casuarius.

Order 4. Apterygiformes:

1. Relatively small, almost wingless, hen like, nocturnal, omnivorous running birds confined to New Zealand.

2. Bills long and slender with nostril at the tip.

3. Wings degenerated with vestigeal hu­merus, only one digit and no flight feathers.

4. Each leg bears four-clawed toes.

5. Body plumage fluffy, hair-like, without after shafts.

6. Sternum un-keeled. The eyes are small. Lays only one white egg at a time. Eggs are largest of that in all living birds.

Example: Apteryx (Kiwi).

Order 5. Dinornithiformes:

1. Turkey-like running birds called Moas of New Zealand, about 3 m tall. Became extinct few centuries back.

2. Feathers with large after shafts and without barbicels.

3. Beak short.

4. Hind limbs massive with four toes.

5. Sternum reduced and un-keeled. Cora­coid, scapula and wing bones reduced or absent.

Example: Dinornis.

Order 6. Aepyornithiformes:

1. Giant flightless Madagascar elephant birds, about 3 m tall, became extinct few centuries back after the extinction of Moas.

2. Wings were relatively tiny but legs stout and powerful and with four toes.

3. Egg size 32 x 24 cm; largest of all known animal eggs; capacity about 10 litres.

Example: Aepyornis.

Order 7. Tinamifarmes:

1. Partridge or quail-like, almost tailless, herbivores, essentially cursorial birds, known as Tinamon, can fly clumsily over a short distance, confined to Southern Mexico and Central and South America.

2. Sternum is keeled, and the palate palaeognathus.

3. Pygostyle reduced.

4. The eggs with glossy white shell and incubated by males.

Examples: Crypturellus, Eudromea, etc.

Superorder Impennae:

Evolved from ancestors having wings used for both swimming and flight and gradually changed to form an effective paddle for swimming. The superorder has only one order.

Order Spheniseiformes:

Gregarious, penguins, wonderfully adapted to swimming and diving, confined to the southern part of South America, South Africa Australia, Antarctic regions and Galapagos Islands.

1. Body sleek, streamlined, and offers least possible resistance to diving and sub­marine activities.

2. Closely packed plumage; feathers small, scale-like, dense, over entire body without apteria.

3. Hind limbs modified for swimming; metatarsal, unlike those of other birds only partly fused. The feet are strongly webbed.

4. The integument is provided with, thick, fatty, insulating layer.

5. The bones, excluding certain skull bones, are solid. Air sacs absent.

6. The bones of featherless wings flat­tened and united to form a powerful, resis­tant paddle or flipper moving only at the shoulder joint.

7. Monogamous and one egg is laid at a time. Feed on fishes, crustaceans, squids, etc.

Examples: Aptenodytes, Pygoscelis, Eudyptes, Eudyptula, Spheniscus, etc.

Superorder Neognathae:

1. Modern birds with well-developed wings, keeled sternum, and fully adapted for flight.

2. Beaks without teeth.

3. Slender vomer separates the palatines imperfectly.

4. The palatines are protruded posteri­orly and in contact with the base of cranium and remain movably articulated with small pterygoids.

5. Tail vertebrae 5 or 6. Pygostyle absent.

6. Forelimbs with metacarpals joined, and fingers included in wings.

Order 1. Gaviiformes:

1. Piscivorous sea or lake-birds of North America, Europe and Arctic, adapted for diving and swimming. Capable of flight also.

2. The neck is long. Legs are posteriorly placed and completely encased with skin.

3. The digits webbed; wings short.

4. Eggs are laid in nests among piles of vegetation.

Example: Gavia.

Order 2. Podicipitiformes:

1. Fresh water, agile, compact-bodied .divers or grebes, almost cosmopolitan in distribution.

2. Toes lobate.

3. The reduced tail bears degenerated tail feathers.

4. Lungs are placed far back.

Examples: Podiceps, Aechmophorus, Podilymbus, Centropelara, etc.

Order 3. Procellariformes:

1. Tube-nosed, long-winged sea birds, including albatrosses, fulmars, petrels etc., enjoying cosmopolitan distribution. Come to land only in breeding season and build-up nest in holes.

2. Nostril tubular, arid horny sheath of hooked bill composed of several plates.

3. Hind toe vestigeal or none (as in diving petrels).

4. Plumage compact and oily.

5. Wings long, narrow, span may be over 3 metre.

Examples: Diomedea, Puffinus, Oceano- droma, Pachyptila, Pelecanoides, etc.

Order 4. Pelecaniformes:

1. Voracious fish-eaters, diving pelicans, cormorants, boobies, gannets, etc. with all 4 toes included in the foot-web.

2. Nostril vestigeal or absent.

3. A gular pouch or throat, except in tropical birds.

4. In pelicans, body is heavy, bill up to 45 cm. long, pouch used to scoop fishes from water.

Examples: Pelecanus, Phalacrocorax, Sula, Anhinga, Fregata, Phaethon, etc..

Order 5. Ciconiiformes:

1. Long-necked, long-billed, herons, storks, ibises, flamingos, feeding principally in tropical and subtropical marshes and mudflats.

2. They are either with decorative plum­ages, bare areas on head (storks); bill abruptly de-curved at middle (flamingos).

3. The pattern of beak varies and with sharp cutting edges.

4. Except flamingos web between the toes are absent.

5. Speedy fliers; legs adapted for quick walking cm mudflats.

Examples: Ardea, Egretta, Nycticorax, Bnlaenkeps, Scopus, Ciconia, Threskiornis, Plegadis, Phoenicopterus, etc.

Order 6. Anseriformes:

1. About 200 species of swans, geese and ducks, all are efficient fliers and almost cosmopolitan in distribution.

2. Bills broad, covered with soft cornified epidermis containing numerous sense pits with harder cap at tip. The margins of bill with many transverse horny lamellae (ridges).

3. Tongue fleshy, legs short. Feet webbed. The tail is usually short and many feathered.

Examples: Ansera, Coscoroba, Anas, Branta, Cairina, Somateria, Polysticta, Mergus, Oxyura, etc.

Order 7. Falconiformes:

1. The powerful, predaceous birds like vultures, kites, hawks, falcons, eagles etc. are distributed almost everywhere except Antarctica.

2. They are notable for the spread of their sharp claws for catching and holding prey and their stout hooked beaks for cutting and tearing.

3. Mandible sharp-edged.

4. Feathers are stiff.

5. Eyes laterally placed and with ex­tremely sharp power of vision.

6. They feed on living vertebrates includ­ing fish and, in some cases, even insects.

7. Mostly monogamous. Females incu­bate eggs. The males feed the females dur­ing incubation.

Examples: Gypes, Gymnogypes, Aegypices, Haliaster, Aquila, Buteo, Circus, Falco, Accipiter, etc.

Order 8. Galliformes:

1. Gregarious, non-migratory, ground dwelling game-binds, grouse, quail, pheas­ants, turkeys, etc., cosmopolitan in distribu­tion.

2. The head is small and body compact.

3. The legs are massive, clawed and used for scratching soil for searching food. Three toes are anteriorly directed.

4. Wings, in the majority, short and round.

5. The beaks are strong built, arched, suitable for picking up grains or seeds.

6. Males are aggressive polygamous.

Examples: Crax, Lagopus, Alectoris, Cotumix, Frauedinus, Phasianus, Paw, Melagris, Opisthocomus, etc.

Order 9. Gruiformes:

1. The order includes polymorphic forms, either of large size and strong flight, inhab­iting open marshes or prairies (cranes) or of medium to small size, of weak flight, or flightless, and shy inhabitant of marshes enjoying cosmopolitan distribution except in poles.

2. Toes are not webbed. Nest may be built on the ground.

Examples: Grus (Cranes), Rallus, Fulica, Gallinula, Otis, Rhynochetos, Turnix, Monias, etc.

Order 10. Diatrymiformes:

Large flightless European and North American terrestrial birds with massive head, beak and neck; lived in the Eocene period. They were perhaps allied to the cranes.

Example: Diatryma.

Order 11. Charadriiformes:

Shore birds, gulls, auks etc. are univer­sally distributed, except in poles.

1. The order comprises of variety of forms, which live near water, some in shore, some in aquatic leaves and some are aquatic.

2. Plumage dense and firm.

3. Toes usually webbed, at least at the base.

4. More or less long-legged (shore birds), strong-winged (gulls), or with only 3 toes and legs far back in position.

5. Eggs heavily spotted.

Shore birds probe for food in sand, mud or shallow waters.

Examples: Charadrius, Jacana, Rostratula, Haemantopus, Vanellus, Gallimgo, Galidris, Numenius, Dromas, Glareola, Larus, Fratercula, Alca, etc.

Order 12. Columbiformes:

Pigeons and doves, distributed world­wide except in poles.

1. Herbivorous, size varies from swan to pigeon.

2. The wings are long, pointed and en­able the birds to make sustained flight at a great speed.

3. Bills short and slender; the base of beak covered by a soft skin bearing longi­tudinal slit-like nostril called cere.

4. The head and neck small and compact.

5. Legs are small. All the toes lie in same plane and are provided with straight tarsus usually shorter than toes.

6. The crop is large producing ‘pigeon milk.’

7. Monogamous but lives in groups.

8. Young are helpless and both male and female nourish the young with the help of ‘pigeon milk’ produced by both sexes during breeding season.

9. Usually lay 2-3 eggs; both male and female incubate the eggs.

One family of this order is extinct which includes Dodo.

Examples: Columbia, Pterocles, Syrrhypta, Streptopelia, Cabonas, Treron, Coura, Didunculus, etc.

Order 13. Psittaciformes:

1. These are parrots distributed in forests of tropics and subtropics; concentrated in Australia, New Zealand, and South America. Adapted for arboreal life and can also climb.

2. Loud-voiced birds, chiefly frugivorous with brilliant plumage of green, blue, yellow or red.

3. Beak stout, narrow, sharp-edged, and hooked at the tip used for climbing.

4. The upper mandible is movably articu­lated with the frontal bone of the skull.

5. Bill with soft cere, often feathered.

6. The toes two in front and two behind, the outer hind toe is not reversible. Used for grasping.

7. Live in flocks, but strictly monoga­mous. The nest is built in the holes of trees.

8. The young are nourished till they attain maturity.

Examples: Ara (Macaw), Kakatoe, Psittacus, Conuropsis, Melapsittacus, Agapomis, Psittacula, Nestor, Rhynchopsitta, etc.

Order 14. Cuculiformes:

Tropical and subtropical cuckoos, road- runners, anis, etc., common in temperate zones also.

1. Toes are two in front, and two behind. Outer toe reversible; the feet are not adapted for grasping.

2. Bill moderate, tail long.

3. Many old-world cuckoos are parasitic, the females lay eggs in the nest of other birds like crow, for incubation and rearing of young.

Examples: Cuculus, Chalecites, Qeococcyx, etc.

Order 15. Strigiformes:

The order includes nocturnal birds, the owls, which prey upon small animals at night.

1. Plumage soft-textured. The outer vane of each outermost wing feather is narrow to constitute a loose fringe, making a soundless flight and approach possible.

2. Head large and round. Owl rotates its neck to look sideways.

3. The beak is short.

4. Feet adapted for grasping, claws sharp.

5. Ear openings large, often with flap-like cover, sometimes asymmetrical.

6. Eyes large, round, directed forward and each in a disc of radial feathers.

7. Retina contains principally rods to perceive low intensity light.

8. The prey is swallowed whole.

9. Eggs are white. Nests are built in holes of trees or buildings.

Examples: Bubo, Tyto, Asio, Otus, Claucidium, Speotyto, Nyctea, etc.

Order 16 : Podargiformes: 

1. Tropical, subtropical and temperate; nocturnal night hawks, whippoorwills, etc. living in woods or bush, forage near ground or high in air, and prey on insects at night or dusk.

2. Colouration protective, helps the bird in concealing.

3. Plumage soft-and arranged in the fashion of that of owl.

4. Legs and feet small and weak, not adapted for grasping.

5. Bills are small, delicate, but the mouth opening wide and margined with long bristle-like feathers with specialised sensory receptors.

Examples: Podargus, Nyctibius, Chordeiles, Caprimulgus, Nyctidramus, etc.

Order 17. Apodiformes (Micropodi- formes):

Small swifts and humming birds, mostly tropical.

1. Legs very short, feet very small, wings pointed and bills small and weak (swifts) or slender with long tubular tongue (humming birds).

2. In swifts the mouth is broad and eyes are large.

3. In humming birds, plumage is bril­liant, iridescent, specially on head and neck of males.

4. Feed on nectar, small insects and spiders from the blossom by tubular protrusible tongue and needle-like bill.

5. Eggs are white.

Examples: Apus, Cypsiurns, Chaetura, Patagona, Loddigeria, etc.

Order 18. Coliiformes:

1. Small (27.5-35 cm), passerine-like, colies or mouse birds of Southern Africa with short legs, sharp curved claws. Live in a group of 20 to 30.

2. The 1st and 4th toes reversible, which help in creeping on trees.

3. The feathers hair-like and soft; tail very long.

4. Usually a crest is present on the head.

Example: Colius.

Order 19. Trogoniformes:

1. Small Trogons and Quatjals of Asia, Africa and Tropical America, lead a solitary life in dense forest and capture insects in the early morning or during twilight.

2. The bills are short, and stout with bristles at the base. The tip of the beak hooked and, in some, indented.

3. Feet small and weak. The 1st and 2nd toes are directed backwards and 3rd and 4th toes anteriorly placed.

4. Feathers soft and lax, help in noiseless flight.

5. Tail long and stiff, supports against vertical surface at the time of digging.

Examples: Herpaetes, Hypodermes, Calures, Pharomechrus, etc.

Order 20. Coraciiformes:

1. Brilliantly-coloured kingfishers, horn- bills, motmots, bee-eaters, rollers, and hoo­poes, found world-wide, especially in tropi­cal climates, show varied structures.

2. In most, wings and legs are short and beak long.

3. In some, anteriorly directed toes are fused at the base (syndactylous) and in others one of the toes is reversed (zygodac- tylous).

4. Nests are built in holes of trees, etc.

Examples: Alcedo, Ispidina, Dacelo, Chlorocerle, Merops, Coracis, Upupa, Buceros, Anthracoceros, etc.

Order 21. Piciformes:

1. Woodpeckers, jacamars, puffbirds, barbets, honey guides, toucans, enjoying world­wide distribution, except in Australia and poles; live in forest, cling to the tree trunk, dig insect and its larvae out of wood and excavate nest cavities in trees.

2. The feet is zygodactylous. 2nd and 3rd toes are directed forward and 1st and 4th pointed backward.

3. Tail feather stiff with pointed tips.

4. Bill stout, tongue protrusible, roughed, or with barbs near tip.

Examples: Picus, Sphyrapicus, Pynx, Indi­cator, Ramphastos, Notharcus, Megalaima, etc.

Order 22. Passeriformes:

1. Small perching birds or passerines, adapted to various habitats and distributed widely. The order includes about 5,100 known species.

2. All are adapted for land life and the four digits remain in the same level.

Examples: Muscivora, Tyrannus, Xenicus, Acanthisitta, Oxyruncus, Menura, Pycnonotus, Aegithnia, Lanius, Dulus, Corvus, Pica, Sturnus, Passer, Fringilla, Aethopyga, Moho, etc..

Class Reptilia

Class Reptilia 

Introduction

These were the first class of organisms to adapt to life on land. They are believed to have evolved from the amphibians millions of years ago. There are about 10000 different species of reptiles on earth. They are cold-blooded animals belonging to the phylum Chordata of Animal kingdom.

The skull of the reptiles is modified that gives the reptiles an efficient and powerful jaw action. The modification also makes the skull light.

Characteristics of Reptilia

Following are the important characteristics of the animals belonging to Class Reptilia:

These are creeping and burrowing terrestrial animals with scales on their body.

They are cold-blooded animals found in most of the warmer regions of the world.

Their skin is dry, and rough, without any glands.

The body is divided into head, neck, trunk, and tail.

Few of these shed the scales on their skin as skin cast.

The respiration takes place with the help of the lungs.

The skull is monocondylic.

Limbs may or may not be present. If they have limbs, they are two pairs of pentadactyl limbs, each bearing claws. Snakes do not have limbs.

The heart is 3 chambered. However, crocodiles have a 4-chambered heart.

The nervous system comprises 12 pairs of cranial nerves.

Reptiles do not have external ear openings. Tympanum represents ear

They possess a typical cloaca.

Reptiles are generally uricotelic. They mostly excrete nitrogenous wastes as uric acid.

Fertilisation is internal.

They are oviparous and the eggs are very yolky. Development is direct.

E.g., Snakes, Turtles, Lizards, Crocodiles.

Classification of Reptilia

The class Reptilia is differentiated into three major sub-classes:

Anapsida

Parapsida

Diapsida

1.Anapsida

The dermal bones form a complete roof over the skull with no temporal fossae.

These are sub-divided into Cotylosauria and Chelonia.

Modern chelonians are classified according to the method of retracting the head in the shell.

Turtles, tortoises, and terrapins belong to this group.

2.Parapsida

These reptiles possess one temporal fossa present high up on the skull.

Protosaurs, Nothosaurs, Placodonts showed this type of skull.

The two largest groups among these were Ichthyosaurs and Plesiosaurus. These became extinct at the end of the Cretaceous period when several other reptiles including dinosaurs died.

3.Diapsida

There are two temporal vacuities in the skull.

They are diverse of all reptiles.

The dinosaurs and pterosaurs are included in this group.

These are divided into two major groups- Archosauria and Lepidosauria.

Eg., Crocodilus, Chameleon.

Groups of Reptiles

The class Reptilia is further divided into different groups known as orders:

Order.                             Examples

Order Squamata.        Lizards, Snakes

Order Testudines.   Turtles, Tortoises, Terrapins

Order Crocodilia.      Crocodiles, Alligators

Order Sphenodontia   Tuataras

Extinct groups of class Reptilia

Ichthyopterygia

Lepidosauria

Archosauria

Synapsida

1.Ichthyopterygia

This group had one temporal fossa place high up on the skull.

The two largest groups belonging to this sub-class are Ichthyosaurs and Plesiosaurs.

Eg., Ichthyosaurus

2.Lepidosauria

These were all the lizard-like reptiles.

They had two temporal vacuities in the skull.

Eg., Youngina,

3.Archosauria

The skulls were diapsid.

Some were bipedal which gave rise to birds.

They also gave rise to dinosaurs.

Eg., Brontosaurus

4.Synapsida

They had one temporal fossa on the lower side of the skull.

These were the most dominant group of reptiles during the Permian period.

The surviving Lepidosaurs in the Mesozoic era gave rise to mammals. The rest were replaced by dinosaurs.

Eg., Plesiosaurus.

Crocodile 

Scientific Classification

Kingdom : Animalia

Phylum. : Chordata

Class : Reptilia

Order. : Crocodilia

Family. : Crocodylidae

Genus. : Crocodylus

Scientific Name : Crocodylus acutus 

Crocodiles are one of the most well-known and fearsome animals in the world and are considered apex predators. Their powerful bodies, strong jaws, and immense speed and agility along with their unparalleled stealth, have led to them being one of the world’s top predators in their natural environments.

Etymology

The word crocodile actually originates from the Ancient Greek word krokódilos or some other slight variation. Latinization of the name turned the “k” into a “c”. Some scholars believe that crocodile is a combination of the word for pebbles (krokè) and for worm (drilos).

Evolution

Crocodiles are closely related to other crocodilians including alligators, caimans, and gharials, crocodiles have changed very little in an evolutionary sense in 200 million years.

Unlike other reptile species, crocodilians are archosaurs which is an ancient group of reptiles that also included dinosaurs.

Although dinosaurs became extinct 65 million years ago, crocodiles are thought to have survived so well over time due to the fact that they are so well suited to their environments.

There are currently 13 different crocodile species that are found inhabiting both fresh and saltwater environments throughout North and South America, Africa, Asia and Australia.

The semi-aquatic nature of Crocodiles has led to them evolving a number of key adaptations that allow them to survive so successfully in their natural environments.

Types

Saltwater crocodile (Crocodylus porosus): Once endangered, this marine monster has since staged an impressive comeback. Known for a penchant for ambushing its prey, it is capable of growing to 20 feet in length and weighing over 4,000 pounds. It is also the largest reptile on the planet and generally has dark green scales, although they may also be tan, or almost black in some cases. The giant reptile can be found in Australia, India, and Micronesia.

Nile crocodile (Crocodylus niloticus): This reptile is known for its extreme aggression and thick scaly skin. It also has a remarkable ability to clamp down powerfully with its jaws for lengthy periods of time. Its favorite hangouts include lakes, rivers, and swamps and it can generally be found in African regions south of the Sahara and parts of Madagascar.

American crocodile (Crocodylus acutus): The only crocodile apart from the saltwater crocodile to have an affinity for saltwater, this species can be found in Florida, Mexico, Peru, and Venezuela.

Hall’s New Guinea crocodile (Crocodylus halli): The giant reptiles can be found in the southern part of New Guinea where they prowl in estuaries, lakes, and rivers.

Orinoco crocodile (Crocodylus intermedius): The largest reptile in the Americas, this crocodilian is known for its pale hide and occupies the Orinoco river Basin in Colombia and Venezuela.

Freshwater crocodile (Crocodylus johnstoni): Unlike their saltwater cousins, these reptiles thrive in freshwater and only reach 3 metres and 220 pounds at the maximum. They do live side by side with salties, although they’re no match for the former.

Philippine crocodile (Crocodylus mindorensis): These freshwater crocodiles have golden brown scales that darken with age. They play a key role in maintaining healthy fish stocks in their environs and can grow slightly over 8 feet while weighing a maximum of 200 pounds.

Morelet’s crocodile (Crocodylus moreletii): These reptiles which have webbed posterior feet are rather fast runners. They are recognizable by their dark scales and broad snouts.

New Guinea crocodile (Crocodylus novaeguineae): A separate species from the crocodiles which lie south of the island’s central rige, these reptiles which are found in the north are nocturnal. They have a tapered snout and grey scales.

 Mugger crocodile (Crocodylus palustris): Known for its light olive coloring, this crocodile can be found in India, Iran, Nepal, Pakistan, and Sri Lanka. It also has a habit of burrowing into the mud to escape scorching temperatures and is the crocodile with the widest snout.

Borneo crocodile (Crocodylus raninus): Found in Borneo, as its name suggests, this species continues to remain something of a mystery to experts.

Cuban crocodile (Crocodylus rhombifer): Highly intelligent, long-limbed, and fond of land, this crocodile cooperates with other members of its species when hunting. Its numbers, however, have plummeted owing to hunting.

Siamese crocodile (Crocodylus siamensis): This species comes with scales ranging from dark to pale green. It is capable of growing to a maximum of 13 feet and 770 pounds.

West African crocodile (Crocodylus suchus): With scales which range from dark to pale, this crocodile is known for being fond of fresh water in forests. However, it has also adapted to deserts in Mauritania where it sits out periods of drought ensconced in caves.

Osborn’s dwarf crocodile (Osteolaemus osborni): This species can be found in the Congo river basin in central Africa.

Dwarf crocodile (Osteolaemus tetraspis): The smallest crocodile species, this reptile grows to about 5 feet and 70 pounds, and can be found in forests or caves.

West African slender-snouted crocodile (Mecistops cataphractus): Something of an enigma to experts, this reptile is recognizable by its pointed snout. It also prefers to live in water filed with plant life.

Central African slender-snouted crocodile (Mecistops leptorhynchus): As its name suggests, this second member of the genus Mecistops, can be found throughout Central Africa. However, it can also be found in Southern Sudan.

Distribution and Habitat

Crocodiles are found in a variety of wetland habitats throughout the warmer tropical waters in the southern Hemisphere. Their inability to internally regulate their body temperature means that they rely heavily on the sun to warm their bodies up after it being cooled by spending time in the water.

Americas

The American Crocodile is the largest crocodilian species in North and South America and is found inhabiting freshwater rivers and lakes, along with brackish coastal waters near estuaries and in lagoons from southern Florida, throughout Central America and into northern parts of South America.

Africa

Over in Africa, the Nile Crocodile was once widespread in eastern and southern Africa but are now scarcer. They inhabit freshwater marshes, rivers, lakes and mangrove swamps. The world’s largest and most widely dispersed crocodile species is the estuarine crocodile.

Asia and Australia

These formidable reptilian giants are found in river mouths and brackish swamps from the Bay of Bengal in the Indian Ocean, across to and throughout Southeast Asia and down into Australia.

Anatomy and Appearance

Crocodiles are large-sized reptiles with thick, scaly skin that is made up of armored, waterproof plates that both protects them from potential predators and also prevents their bodies from drying out.

These scales come in a variety of colors from dull olive and green, to brown, greys and black meaning that they are very easily camouflaged in the surrounding water and vegetation.

Like other crocodilian species, their eyes and nostrils are located on the very top of their broad head and snout.

This is useful as they lie in wait in the water with almost none of their bodies exposed in order to more successfully ambush prey.

In order to protect them in the water, crocodiles have a special transparent third eyelid which allows them to leave their eyes open but prevents damage from the water.

They also have external flaps that close off their ears and nostrils, and a special respiratory system that allows them to remain in the water for up to five hours at a time.

Their vertically flattened tails are immensely strong and are used to propel them through the water, as although they do have webbed feet, they do not use them to aid them when swimming.

Crocodiles range in size from the less than 2 meter long dwarf crocodile to the 7 meter long estuarine crocodile (also known as the saltwater crocodile or “saltie”), which is the world’s heaviest reptile weighing up to 1,000kg.

Behavior and Lifestyle

Crocodiles have been extensively studies by many researchers and scientists to understand their behavior better. Although many species are mainly reclusive and haven’t been extensively studied, here are some common behavioral patters found in crocodiles.

Inability to regulate Body Temperature

In the same way as other reptiles, crocodiles are not able to regulate their body temperature themselves and instead rely heavily on the heat of the sun to warm their enormous bodies. During the hot daylight hours, they bask in the sun on the riverbanks warming their bodies up from a night of hunting. Smaller species like the dwarf crocodile (which is the least-known of the crocodile species) are also known to climb trees in order to bask on the branches.

Another way crocodiles are able to regulate their body temperature is by bobbing up and down in the water, warming in the sun on the surface and cooling themselves down beneath it. Crocodiles are highly sociable animals that remain together in large, mixed groups of adults and juveniles.

Crocodiles are Social Animals

Behavior such as hierarchy, and group feeding have been observed in many of the species. The biggest male is on the top of the hierarchy ladder, and they get to enjoy the best spots for basking. The females always get preference during group feedings when a large animal has been felled by the group. This behavior has especially been observed in the Nile crocodiles and the Mugger crocodiles.

This changes when the mating season begins, the males become highly territorial and protect their stretch of river bank from intrusion by competitors by rearing their large heads high up into the air and roaring at intruders. When female Nile crocodiles are attracted by these noises, the males begin to thrash their bodies around and even shoot water into the air from their nostrils.

Crocodiles Communication

Unlike many other reptiles crocodiles have the ability to communicate with each other. Depending upon the species in question, the size, the sex, and the situation or condition they are in, crocodiles make a variety of sounds to communicate. Here are some common sounds and their meaning:

1.Chirping – When the eggs are about to hatch, the hatchlings inside the eggs make a ‘squeaky’ noise which prompts the mother to carry the eggs into the water with her mouth. The eggs then hatch in the water and the mother keeps the hatchlings in the water, protecting and feeding them over a period of time.

2.Distress – When the young crocodiles are in imminent danger or they feel threatened, they emanate a high-pitched sound that can alert other crocodiles in the area.

3.Hiss – When they want to threaten others, whether crocodiles or other animals and prey, they make a sound akin to a coughing noise.

4.Mating call – female crocodiles make a specific noise called the hatching call.

5.Bellowing – The male crocodiles make a bellowing noise which is a combination of an infrasonic vibration that creates ripples in the water and a vibration in the ground itself. This commonly happens during mating season in spring. Crocodiles also use this noise to scare off other predators and threats in the area.

Cognitive Intelligence

Crocodiles are highly observant and they study the behavior of their prey extensively. They study the usual patterns in the behavior of animals that come to drink water near their habitat. Some crocodiles have used nesting materials to lure birds close enough to grab them.

Crocodiles are cooperative-group-hunters. They swarm larger preys while big crocodile holds it down and others kill it by ripping it apart. They also trap fish by circling them in groups and snatching them one by one.

Crocodiles are have displayed playful behavior common in social structures, such as locomotive play like repetitive rolling on the slopes, playing with objects, social play like wrestling, swimming and riding ach others backs are common sight in crocodile societies.

Reproduction and Life Cycles

After mating, the female crocodile lays between 17 (dwarf crocodiles) and 100 (Nile crocodiles) eggs in a nest made up of soil and vegetation such as leaves, which prevents the eggs from becoming too cold should the nest become flooded during incubation. In areas prone to flooding, they are also known to build nest mounds to raise the egg out of the danger from flood waters.

The incubation period is usually around 3 months long with hatchlings often emerging to coincide with the beginning of the rainy season to prevent their bodies from drying out. Despite their fearsome reputation, female crocodiles are incredibly caring mothers and guard their nests fiercely to protect them from predators until they are ready to hatch. Once the hatchlings begin to emerge, the female crocodile then helps them down to the water by carrying them in the throat pouch in her mouth.

Interestingly the thin-shelled, leathery eggs of crocodiles (and indeed other more modern reptile species) was an evolutionary breakthrough for many species as their protective layer and waterproof nature meant that females could lay their eggs on land rather than in water, even in the driest of places, meaning they could be better protected from predators. Typically, crocodiles have a lifespan of 25 to 75 years.

Diet and Prey

Crocodiles are carnivorous, formidable predators and at the top of the food chain in their natural habitat. Their inability to chew food has led to the development of ambush hunting techniques, and strong powerful jaws with teeth that are used to tear food apart.

Young crocodiles rely heavily on fish, crustaceans, and small mammals, birds and reptiles, but as they grow larger they are able to take much bigger prey species including, deer, zebra and water buffalo.

Crocodiles are often more active during the night, with some species being known to venture onto land to catch prey, livestock and in some cases, people (learn more about the most dangerous animals on earth to humans).

Due to their highly sociable nature, Nile crocodiles (which predominantly feed on fish), are known to work together in order to cordon fish off in sections of river when they are migrating.

Crocodiles have a very slow metabolism and can float for a long time without moving.

In extreme cases, they seem to be able to go dormant and live off of their own tissues for long periods.

Crocodiles can live for up to three years without eating.

Catfish make up a large portion of their natural diets and by keeping their numbers at bay, this allows small fish species to still thrive. These fish (which would ordinarily be quickly eaten by the larger catfish) then provide food for over 40 species of bird, that in return fertilize the waters with their droppings and keep them rich with nutrients so numerous animal species can continue to thrive.

Predators and Threats

Due to the large size and highly aggressive nature of these apex predators, adult crocodiles have very few predators within their natural environments with the exception of occasional takings by big cats such as lions, jaguars, and tigers. The smaller and much more vulnerable juveniles however are preyed upon by a number of animal species around the world from wild pigs, dogs, and large reptiles to birds of prey like eagles.

Although they are common in certain areas, crocodiles are threatened throughout much of their natural ranges from hunting, habitat loss, and ecological changes further down the food chain due to overfishing or water pollution, which then has an impact on them higher up the food chain.

Interesting Facts and Features

Although most crocodile species inhabit freshwater regions such as swamps, rivers, and lakes, there are a number of species that venture into more salty waters around the coasts. American crocodiles are often found in estuaries and lagoons close to the shores but are able to deal with the higher salinity levels by drinking large amounts of freshwater whenever possible, and by removing salt from the body by secreting crocodile tears through the glands on their face.

In periods of drought, they are also known to burrow deep into the mud in order to stop their bodies from drying out and will not eat anything until the water returns. On the other side of the world, estuarine crocodiles have been observed eating pebbles found on the riverbeds. The process of this is thought to help to grind up their food, therefore aiding digestion but also acts as a ballast to help with buoyancy while floating on the surface of the water.

Crocodile vs Alligator

As noted earlier, the order Crocodilia encompasses crocodiles, alligators, gharial, and caimans. With alligators being common across the Southeastern United States, a common question is what are the key differences between alligators vs. crocodiles? The two differ most in that:

Crocodiles have a more pointed (V-shaped) snout while an alligators’ is ‘U-shaped.’

Crocodile species such as saltwater crocodiles can grow much larger than American alligators.

American alligators lack a salt gland and primarily live in freshwater while American crocodiles are far more adaptable to saltwater environments.

Commercial Use of Crocodiles

1.Crocodile skin – As formidable as they are crocodiles are farmed in many parts of the world for their hide, which is tanned and turned into apparel, shoes, handbags, belts, etc. Crocodile skin is highly sought after and valuable in the high fashion industry across the globe.

2.Crocodile meat – The meat is harvested as it is considered a delicacy and eaten in various countries such as China, Thailand, Cambodia, Korea, Philippines, New Zealand, Bahamas, and even the USA.

3.Crocodile oil – Monounsaturated and polyunsaturated fats are extracted from the tissues of the crocodile and sold as crocodile oil. It was extensively used in traditional medicine in many Asian and native cultures. It is used in treating skin conditions, mending wounds and skin tissue, and treating illnesses such as cancer.

Conservation Status

Today, although some local populations are thought to be stable, throughout much of their natural ranges the population numbers for all crocodiles species are declining. Out of the 13 different crocodile species, 6 has been listed as Least Concern, 2 have been listed as Vulnerable and 5 have been listed as Critically Endangered by the IUCN. Of all of these species, the Philippine crocodile is by far the most at risk with less than 200 individuals estimated to remain in the wild.