Heron

The herons are long-legged, long-necked, freshwater and coastal birds in the family Ardeidae, with 64 recognised species, some of which are referred to as egrets or bitterns rather than herons. Members of the genera Botaurus and Ixobrychus are referred to as bitterns, and, together with the zigzag heron, or zigzag bittern, in the monotypic genus Zebrilus, form a monophyletic group within the Ardeidae. Egretsdo not form a biologically distinct group from herons, and tend to be named differently because they are mainly white or have decorative plumes in breeding plumage. Herons, by evolutionary adaptation, have long beaks.

The classification of the individual heron/egret species is fraught with difficulty, and no clear consensus exists about the correct placement of many species into either of the two major genera, Ardea and Egretta. Similarly, the relationships of the genera in the family are not completely resolved. However, one species formerly considered to constitute a separate monotypic family, the Cochlearidae or 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, while others, notably the bitterns, use reed beds. A group of them is called a "siege."[2]

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 dwarf bittern, which measures 25–30 cm (10–12 in) in length, although all the species in the genus Ixobrychus are small and many broadly overlap in size. The largest species of heron is the goliath heron, which stands up to 152 cm (60 in) tall. The necks are able to kink in an S-shape, due to the modified shape of the cervical vertebrae, of which they have 20–21. The neck can 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 backwards. The feet of herons have long, thin toes, with three forward pointing ones and one pointing backwards.[3]

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 and other bare parts of the body are usually yellow, black, or brown in colour, although this can vary during the breeding season. The wings are broad and long, exhibiting 10 or 11 primary 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, little sexual dimorphism in plumage is seen (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.[3] In the Pacific reef heron, both dark and light colour morphs exist, and the percentage of each morph varies geographically. White morphs only occur in areas with coral beaches.[4]

A beige heron with yellow legs and bill stands hunched, its neck is hidden in the feathers of the body, on a wire mesh above water.
The neck of this yellow bittern is fully retracted.
two herons, one with white plumage and one with slate grey, on a rock in the surf of the ocean
The Pacific reef heron has two colour morphs, the light and the dark.
Lava heron, grey with a long bill and red feet and with small fish in bill amongst grey rocks
Lava herons are endemic to the Galápagos Islands, where they feed on fish and crabs in the intertidal and mangrove areas.
A great egret manipulating its prey, a lizard, before swallowing
Black herons holding wings out to form an umbrella-like canopy under which to hunt
Tricoloured heron fishing, using wings to create shade
The larger bitterns, like this American bittern, are solitary breeders. To advertise for mates, males use loud, characteristic calls, referred to as booming.