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For other uses, see Heron (disambiguation).
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 Snowy Egret, Egretta thula. Note the chicks in the nest. | ||||||||||
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See text. |
The herons are wading birds in the Ardeidae family. Some are called egrets or bitterns instead of herons. 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 or have decorative plumes.
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 universally regarded as a member of the Ardeidae.
Although herons resemble birds in some other families, such as the storks, ibises and spoonbills, they differ from these in flying with their necks retracted, not outstretched. They are also one of the bird groups that have powder down.
The members of this family are mostly associated with wetlands, and prey on fish, frogs and other aquatic species. Some, like the Cattle Egret and Black-headed Heron, also take large insects, and are less tied to watery environments. Some members of this group nest colonially in trees, others, notably the bitterns, use reedbeds.
In February 2005, the Canadian scientist Dr. Louis Lefebvre announced a method of measuring avian IQ in terms of their innovation in feeding habits. Herons were named among the most intelligent birds based on this scale, reflecting a wide variety, flexibility and adaptiveness to acquire food{{ref}}.
Analyses of the skeleton, mainly the skull, suggested that the Ardeidae could be split into a diurnal and a crepuscular/nocturnal group which included the bitterns. From DNA studies and skeletal analyses focusing more on bones of body and limbs, this grouping has been revealed as incorrect (McCracken & Sheldon 1998). Rather, the similarities in skull morphology reflect convergent evolution to cope with the different challenges of daytime and nighttime feeding. Today, it is believed that three major groups can be distinguished (Sheldon et al. 1995, 2000), which are (from the most primitive to the most advanced):
Bare-throated Tiger Heron, Tigrisoma mexicanum
The night herons could warrant separation as subfamily Nycticoracinae, as it was traditionally done. However, the position of some genera (e.g. Butorides or Syrigma) is unclear at the moment, and molecular studies have until now suffered from a small number of studied taxa. Especially the relationship among the ardeine subfamily is very badly resolved. The arrangement presented here should be considered provisional.
FAMILY ARDEIDAE
Subfamily Tigrisomatinae
.jpg/58px-Botaurus stellaris (Marek Szczepanek).jpg)
Great Bittern, Botaurus stellaris
Subfamily Botaurinae
Subfamily Ardeinae
Great Blue Heron, Ardea herodias
Fossil herons of unresolved affiliations:
Other prehistoric and fossil species are included in the respective genus accounts.
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