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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".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.
Four Black Herons standing in low water with vegetation holding their wings over their bodies forming what looks like umbrellas
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.
A grey-coloured heron standing up to its chest in water with its wings outstretched and slightly forward of the body looking at highly disturbed water
Tricolored Heron fishing, using wings
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.[
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.
February 18th, 2012
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