The Heron

Aug 19, 2012 Features / Columnists, Interesting Creatures in Guyana

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The herons are long-legged freshwater and coastal birds in the family Ardeidae, with 64 recognised species (some are called ”egrets” or ”bitterns” instead of “heron”).
Within Ardeidae, 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. Some members of this group nest colonially in trees, while others, notably the bitterns, use reedbeds.
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, which can measure under 30 cm (12 in) in length, 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, which stand up to 152 cm (60 in) tall. 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 wings are broad and long, exhibiting 10-11 primaries feathers (the Boat-billed Heron has only nine), 15-20 secondaries and 12 rectrices (10 in the bitterns).
The feathers of the herons are soft and the plumage 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.
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 water birds 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 and bitterns are carnivorous. The members of this family 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. 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.
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.
Courtship usually takes part on the nest. Males arrive first and begin the building of the nest, which 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. Generally herons lay between three to seven eggs. On the whole the eggs are glossy blue or white, with the exception being the large bitterns which lay olive-brown eggs.  (Source: Wikipedia – The Free Online Encyclopedia)

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