Thursday 29 December 2011

FIELD DIARY ON POND HERON

                                    
                                                           Author : Tanmoy Bhaduri

The herons are long-legged freshwater and coastal birds in the family Ardeidae. There are 64 recognised species in this family. Some are called "egrets" or "bitterns" instead of "heron".
Within the family, all members of the genera Botaurus and Ixobrychus are referred to as "bitterns", and — including the Zigzag Heron or Zigzag Bittern — are a monophyletic group within the Ardeidae. However, egrets are not a biologically distinct group from the herons, and tend to be named differently because they are mainly white and/or have decorative plumes. Although egrets have the same build as the larger herons, they tend to be smaller.
The classification of the individual heron/egret species is fraught with difficulty, and there is still no clear consensus about the correct placement of many species into either of the two major genera, Ardea and Egretta. Similarly, the relationship of the genera in the family is not completely resolved. However, one species formerly considered to constitute a separate monotypic family Cochlearidae, the Boat-billed Heron, is now regarded as a member of the Ardeidae.
Although herons resemble birds in some other families, such as the storks, ibises, spoonbills and cranes, they differ from these in flying with their necks retracted, not outstretched. They are also one of the bird groups that have powder down.
Some members of this group nest colonially in trees; others, notably the bitterns, use reedbeds.
Description
The neck of this Yellow Bittern is fully retracted.
The herons are medium to large sized birds with long legs and necks. They exhibit very little sexual dimorphism in size. The smallest species is usually considered the Little Bittern, although all the species in the Ixobrychus genus are small and many broadly overlap in size. The largest species of heron is the Goliath Heron. The necks are able to kink in an s-shape, due to the modified shape of the sixth vertebrae. The neck is able to retract and extend, and is retracted during flight, unlike most other long-necked birds. The neck is longer in the day herons than the night herons and bitterns. The legs are long and strong and in almost every species are unfeathered from the lower part of the tibia (the exception is the Zigzag Heron). In flight the legs and feet are held backward. The feet of herons have long thin toes, with three forward pointing ones and one going backward.
The bill is generally long and harpoon like. It can vary from extremely fine, as in the Agami Heron, to thick as in the Grey Heron. The most atypical bill is owned by the Boat-billed Heron, which has a broad thick bill. The bill, as well as other bare parts of the body, is usually yellow, black or brown coloured, although this colour can vary during the breeding season. The feathers of the herons are soft. The plumage of the herons is usually blue, black, brown, grey or white, and can often be strikingly complex. Amongst the day herons there is little sexual dimorphism in plumage (except in the pond-herons); differences between the sexes are the rule for the night herons and smaller bitterns. Many species also have different colour morphs. In the Pacific Reef Heron there are both dark and light colour morphs, and the percentage of each morph varies geographically. White morphs only occur in areas with coral beaches.
Distribution, habitat and movements
Lava Herons are endemic to the Galápagos Islands where they feed on fish and crabs in the intertidal and mangrove areas
The herons are a widespread family with a cosmopolitan distribution. They exist on all continents except Antarctica, and are present in most habitats except the coldest extremes of the Arctic, extremely high mountains and the driest deserts. Almost all species are associated with water, they are essentially non-swimming waterbirds that feed on the margins of lakes, rivers, swamps, ponds and the sea. They are predominately found in lowland areas, although some species live in alpine areas, and the majority of species occur in the tropics.
The herons are a highly mobile family, with most species being at least partially migratory. Some species are partially migratory, for example the Grey Heron, which is mostly sedentary in Britain but mostly migratory in Scandinavia. Birds are particularly inclined to disperse widely after breeding but before the annual migration where the species is colonial, searching out new feeding areas and reducing the pressures on feeding grounds near the colony. The migration typically occurs at night, usually as individuals or in small groups.
Behaviour
Diet
Great Egret manipulating its prey, a lizard, prior to swallowing
The herons and bitterns are carnivorous. The members of this family are mostly associated with wetlands and water, and feed on a variety of live aquatic prey. The diet includes a wide variety of aquatic animals, including fish, reptiles, amphibians, crustaceans, molluscs and aquatic insects. Individual species may be generalists or specialise in certain prey types, like the Yellow-crowned Night Heron, which specialises in crustaceans, particularly crabs. Many species will also opportunistically take larger prey, including birds and bird eggs, and more rarely carrion. Even more rarely there have been reports of herons eating acorns, peas and grains, but most vegetable matter consumed is accidental.


Black Herons holding wings out to form an umbrella-like canopy to hunt under
The most common hunting technique is for the bird to sit motionless on the edge of or standing in shallow water and wait until prey comes within range. Birds may either do this from an upright posture, giving them a wider field of view for seeing prey, or from a crouched position, which is more cryptic and means the bill is closer to the prey when it is located. Having seen prey the head is moved from side to side, so that the heron can calculate the position of the prey in the water and compensate for refraction, and then the bill is used to spear the prey.

In addition to sitting and waiting, herons may feed more actively. They may walk slowly, at around or less than 60 paces a minute, snatching prey when it is observed. Other active feeding behaviours include foot stirring and probing, where the feet are used to flush out hidden prey. The wings may be used to frighten prey (or possibly attract it to shade) or to reduce glare; the most extreme example of this is exhibited by the Black Heron, which forms a full canopy with its wings over its body.
Some species of heron , such as the Little Egret and Grey Heron, have been documented using bait in order to lure prey to within striking distance. Herons may use items already in place, or actively add items to the water in order to attract fish. Items used may be man made, such as bread; alternatively Striated Herons in the Amazon have been watched repeatedly dropping seeds, insects, flowers and leaves into the water to catch fish.
Three species, the Black-headed Heron, Whistling Heron and especially the Cattle Egret are less tied to watery environments and may feed far away from water. Cattle Egrets improve their foraging success by following large grazing animals, catching insects flushed by their movement. One study found that the success rate of prey capture increased 3.6 times over solitary foraging.
Breeding
The larger bitterns, like this American Bittern, are solitary breeders. To advertise for mates, males use loud characteristic calls, referred to as booming
While the family exhibits a range of breeding strategies, overall the herons are monogamous and mostly colonial. Most day-herons and night-herons are colonial, or partly colonial depending on circumstances, whereas the bitterns and tiger-herons are mostly solitary nesters. Colonies may contain several species as well as other types of waterbird. In a study of Little Egrets and Cattle Egrets in India the majority of the colonies surveyed contained both species.[9] Nesting is seasonal in temperate species; in tropical species it may be seasonal (often coinciding with the rainy season) or year-round. Even in year-round breeders nesting intensity varies throughout the year. Tropical herons typically have only one breeding season per year, unlike some other tropical birds which may raise up to three broods a year.
Courtship usually takes part on the nest. Males arrive first and begin the building of the nest, where they display to attract females. In colonial species displays involve visual cues, which can include adopting postures or ritual displays, whereas in solitary species auditory cues, such as the deep booming of the bitterns, are important. The exception to this is the Boat-billed Heron, which pairs up away from the nesting site. Having paired the pair continue to build the nest in almost all species, although in the Little Bittern and Least Bittern only the male works on the nest.
Some ornithologists have reported observing female herons attaching themselves to impotent mates, then seeking sexual gratification elsewhere.
The nests of herons are usually found near or above water. They are typically placed in vegetation, although the nests of a few species have been found on the ground where suitable trees of shrubs are unavailable. Trees are used by many species, and here they may be placed high up from the ground, whereas species living in reedbeds may nest very close to the ground.
Generally herons lay between three to seven eggs. Larger clutches are reported in the smaller bitterns and more rarely some of the larger day-herons, and single egg clutches are reported for some of the tiger-herons. Clutch size varies by latitude within species, with individuals in temperate climates laying more eggs than tropical ones. On the whole the eggs are glossy blue or white, with the exception being the large bitterns which lay olive-brown eggs.
Name
Herons are also known as "shitepokes", or euphemistically as "shikepokes" or "shypokes". Webster's Dictionary suggests that herons were given this name because of their habit of defecating when flushed. The terms "shitepoke" or "shikepoke" can be used as insults in a number of situations. For example, the term "shikepoke" appears in the 1931 play Green Grow The Lilacs, and in the 1943 musical play Oklahoma!.
The 1971 Compact Edition of the Oxford English Dictionary describes the use of "shitepoke" for the small green heron of North America (Butorides virescens) as originating in the United States, citing a published example from 1853. The OED also observes that "shiterow" or "shederow" are terms used for herons, and also applied as derogatory terms meaning a "thin weakly person". This name for a heron is found in a list of gamebirds in a royal decree of James VI (1566–1625) of Scotland. The OED speculates that "shiterow" is a corruption of "shiteheron".

Tuesday 27 December 2011

STUDIES ON BEHAVIOUR OF HOUSE CROW


STUDIES ON BEHAVIOUR OF HOUSE CROW AT KARNAMADHAVPUR, RAHARA
Author : Tanmoy Bhaduri
Department of Zoology, RKMVC College, Rahara, Kolkata-700118.

Abstract: The House Crow (Corvus splendens ; Aves, Passeriformes, Corvidae) also known as the Colombo Crow, is a common bird of the Crow family, that is of Asian origin but now found in many parts of the world, where they arrived assisted by shipping. It is between the Jackdaw and the Carrion Crow in size (40 cm in length) but is relatively slimmer than either. Due to a human population explosion in the areas it inhabits, this species has also proportionately multiplied. Being an opportunistic omnivorous scavanger has enabled it to thrive in such circumstances. The invasive potential for the species is great all over the tropics. It can travel more than 15 km for feeding. Large trees with big crowns are preferred for nesting. House Crow’s nest is always situated near habitations, in fork close to a tall tree-top, or on outer branches, often in banyan or mango trees. Female builds the nest. During the breeding season, it is seen in pairs, but it usually lives in groups of up to 50 birds. It may become aggressive against raptors. Courtship displays consist of mutual preening and bill-rubbing, occasionally followed by rapid copulation. This behaviour occurs in trees. Breeding season is generally from March to July. During breeding season female crow lays 3-5 eggs, of variable size and colour. Its nest is regularly brood-parasitized by Asian Koel. Four subspecies: C. s. splendens, C. s. zugmayeri ( southern Jammu & Kashmir,Punjab and Rajasthan ), C. s. protegatus (coastal areas, Kerala, Sri Lanka and nearby islets) and C. s. maledivicus  (Maldives islands).
Systematic Position:

Phylum : Chordata

          Class : Aves

                   Subclass : Ornithurae

                             Infra class : Neornithes

                                      Super order : Neognathae           
                                                
                                                  Order : Passeriformes

                                                          Family : Corvidae

                                                                   Specimen : Corvus splendens

Four subspecies: C. s. splendens, C. s. zugmayri (southern Jammu & Kashmir, Punjab and Rajasthan), C. s. portegatus (coastal areas, Kerala, Srilanka and nearby islets), C. s. maledivicus (Maldives islands).

·        The House Crow (Corvus splendens), also known as the Colombo Crow, is a common bird of the crow family, that is of Asian origin but now found in many parts of the world, where they arrived assisted by shipping.
·        It is between the Jackdaw and the Carrion Crow in size 40cm in length, but is relatively slimmer than either. The forehead, crown, throat and upper breast of the birds are richly glossed black, while the neck and breast are lighter grey-brown in colour. The wings, tail and legs are black.
·        There are regional variations in the thickness of the bill and the depth of colour in areas of plumage.
·        House Crow has a widespread distribution in southern Asia, being native to Nepal, Bangladesh, India, Pakistan, Sri Lanka, Maldives and Laccadive Islands, South West Thailand and coastal southern Iran. It has been introduced to East Africa around Zanzibar (around 1897) and Port Sudan, and arrived in Australia via ship but has up to now been exterminated. Recently it has made its arrival in Europe, and has been breeding in the Hook of Holland since 1998. An individual of this species has been present in Cork Harbour on the south coast of Ireland since early September 2010. It is associated with human settlements in all of its range, from small villages to large cities. In Singapore, there was a density of 190 birds/km2 in 2001 with efforts to suppress the population in planning.
·        It is as yet not established in the New World. This species is able to make use of resources with great flexibility and appears to be associated with humans, and no populations are known to exist independently of humans.

·        House Crow is well named “Scavenger Bird”. It feeds mainly on the ground, but also in trees or buildings. It is often seen near rubbish, slaughter-houses, markets and farmlands, beaches close to fisheries or near touristic complexes. It feeds largely on refuse around human habitations, small reptiles and other animals such as insects and other small invertebrates, bird’s eggs, nestlings, grain, fruits, seeds, nectar, berries, amphibians and fishes.

   ·        House Crow is very vocal. It often calls while flying, a typical monotonous, rather dry “kaaa-kaaa-kaaa”. But it also may utter numerous articulated and expressive nodes. It also has a couple of softer calls when resting or during courtship.

·        When in flight, we can see easily the long tail and the slender wings of the House Crow. It appears entirely dark, because the contrast between grey and black is difficult to see. 

·        It is suspected that paramyxoviruses, such as PMV 1, that causes Newcastle disease, that may be spread by Corvus splendens. Outbreaks in India of Newcastle disease were often preceded by mortality in crows. They have also been found to carry Cryptococcus neoformans, which can cause cryptococcosis in humans.