Indian pond heron Ardeola grayii, copyright Lip Kee.

Belongs within: Aequornithia.
Contains: Ixobrychus, Egretta, Nycticorax, Butorides, Ardea.

The Ardeidae include the herons and bitterns, long-billed and -legged fishing birds found worldwide. Characters of the group include a short tail, powder down patches on the breast, rump and sometimes the thighs, and serrations used for grooming along the side of the central forward-directed toe. Basal members of the family include the tiger herons Tigrisoma of South America which resemble bitterns in their cryptic coloration and booming mating calls. The zigzag heron Zebrilus undulatus, another South American species, in primarily grey in colour with light barring.

The night herons of the genera Nycticorax and Nyctanassa are relatively short-necked and stout herons; as indicated by their vernacular name, they are mostly nocturnal in habits. The yellow-crowned night heron Nyctanassa violacea, found in warmer regions of the Americas, is mostly blue-grey with a black head marked by white cheeks and a pale yellow crown. The boatbill heron Cochlearius cochlearius is a Neotropical species with a similar habitus to the night-herons Nycticorax, with a black cap, grey back and pale venter, but with a unique broad beak. This species has historically been classified it in its own family outside the Ardeidae.

The pond herons of the genus Ardeola are stocky herons with relatively short necks and bills found in warmer regions of the Old World.

The stately herons
Published 11 February 2008
White heron or great egret Casmerodius albus, from Wikimedia.

Herons belong to the family Ardeidae, which also includes the bitterns. When I was young and reading Austin (1961), the division of this family was simple—the bitterns formed the subfamily Botaurinae, while everything else fell into Ardeinae. Since then, however, the picture has become a bit more complicated. The bitterns are almost certainly nested within this broad picture of Ardeinae, and most authors have tended to restrict Ardeinae to birds more closely related to the genus Ardea than to the bitterns. Unfortunately, because different authors have found differing positions for the bitterns within heron phylogeny (McCracken & Sheldon 1998), this has resulted in differing contents for Ardeinae.

One point that most authors have agreed on is that the family Ardeidae can be divided into four main groups, whatever their inter-relationships might be. These groups are the day-herons (Ardea and its relatives), night-herons, bitterns and tiger-herons. There are also two single-species genera of more uncertain relationships, Cochlearius and Agamia. The South American tiger-herons have been regarded in the past as closely related to the day-herons on the basis of osteological data (Payne & Risley 1976), but DNA-DNA hybridisation and vocal data position them as the basalmost group in the Ardeidae (McCracken & Sheldon 1998). Unfortunately, heron phylogeny does not appear to have been given much attention since the DNA-DNA hybridisation days, and the only study I found referred to that used (barely) more advanced molecular methods (Chang et al. 2003) seems to have not included tiger-herons. Payne & Risley (1976) took a conservative approach that referred to each of the four groups as separate subfamilies whereas Kushlan & Hancock (2005) included both the night-herons and day-herons in the Ardeinae and placed the other two groups in separate subfamilies. Kushlan & Hancock (2005) also recognised a separate subfamily each for Cochlearius and Agamia, but I suspect this more reflects their uncertain relationships rather than any positive idea about their positions.

Chinese pond-heron Ardeola bacchus, from here.

The day-herons (Ardeinae proper or tribe Ardeini, depending on whom you ask—Kushlan & Hancock, 2005, divide them into two tribes Ardeini and Egrettini, but that isn’t an approach I’ve seen elsewhere) are the best-known of the groups, and include what most people associate with the name “heron”—long-necked, long-legged, stately birds. As well as the herons of the genus Ardea, this group also includes the egrets (Egretta) and the pond-herons in Ardeola and Butorides. As the common name indicates, the day herons are largely diurnal. The males of a number of day heron species (most notably members of the genus Egretta) produce long decorative plumes in the breeding season, as can be seen in the photo of Casmerodius.

The night herons (Nycticoracini or Nycticoracinae) of the genera Nycticorax and Gorsachius are generally shorter, stouter birds than the day herons, with relatively shorter beaks, as well as (obviously) being nocturnal or crepuscular. Osteological data suggest that the night herons are closely related to the bitterns, while molecular data would place them closer to the day herons (McCracken & Sheldon 1998). One night heron genus, the American Nyctanassa, is included by Kushlan & Hancock (2005) among the day herons as opposed to with the other Old World night herons.

Boat-billed heron Cochlearius cochlearius, from Brian Switek.

The boat-billed heron Cochlearius cochlearius and the agami heron Agamia agami are both South American oddballs that have been particularly difficult to place among the herons. In the case of Cochlearius, it was regarded as distinct enough that Wetmore placed it in its own separate family. Cochlearius differs from other herons in its unique beak structure and the number of powder-down patches on the chest (four as opposed to three). However, Cracraft (1967) claimed that, except for features directly connected with the beak, Cochlearius was little different osteologically from Nycticorax, and in fact resembled Nycticorax more closely than the other night-heron genus Gorsachius did! While osteological data might indicate that Cochlearius is simply a very specialised night heron, DNA-DNA hybridisation data indicated a more basal position, around the level of the tiger-herons (though unresolved as to which of the two was the basalmost clade—McCracken & Sheldon 1998). Whichever is the true position, it is clear that the boat-billed heron is highly specialised, though we have little idea what, in fact, it is specialised for—Biderman & Dickerman (1978) found little apparent difference in diet and foraging behaviour of boat-billed herons from more typical heron species, and were only able to suggest somewhat half-heartedly that the oversized beak might be related to courtship displays.

Agami heron Agamia agami, from Arthur Grosset.

The agami heron Agamia agami seems to be a specialist bank feeder (Payne & Risley 1976). In proportions, it is much like a day heron, and osteological data also associates it with that group. However, if it is a day heron, it differs in a number of characteristics from the other members of that group. As can be seen in the photo above, it is a particularly colourful bird, and it is distinct from the day herons in many features of its adult and juvenile plumage. It also has a particularly slender, needle-like bill. The relationships of Agamia do not seem to have yet been investigated molecularly.

Systematics of Ardeidae
<==Ardeidae [Ardeae, Ardeiformes, Ardeinae, Ardeini, Botaurinae, Erodii, Tigriornithini]BKB15
    |--Calcardea Gingerich 1987JM14, MR07
    |    `--C. junnei Gingerich 1987M09
    |--Proardea Lambrecht 1933JM14, M02
    |    `--*P. amissa (Milne-Edwards 1892) [=Ardea amissa, Egretta amissa]M02
    |--Proardeola Harrison 1979JM14, M02
    |    `--*P. walkeri Harrison 1979M02 (see below for synonymy)
       |    |--T. brasilienseSS66
       |    |--T. cabanisiS18
       |    |--T. fasciatumBKB15
       |    |--T. lineatumBKB15
       |    `--T. mexicanumJT12
       `--+--Cochlearius Brisson 1760BKB15, B94 [incl. Cancroma Linné 1766B94; Cancromini, Cochleariidae, Cochleariini]
          |    `--C. cochlearius (Linnaeus 1766) [=Cancroma cochlearius]W51
          |         |--C. c. cochleariusFS55
          |         |--C. c. panamensis Griscom 1926 [=C. zeledoni panamensis]W51
          |         `--C. c. zeledoniFS55
             |  `--Zebrilus Bonaparte 1855BKB15, B94 [Zebrilini]
             |       `--Z. undulatusBKB15
             `--+--+--Syrigma sibilatrixBKB15
                |  `--EgrettaBKB15
                `--+--+--Nyctanassa violaceaBKB15
                   |  `--NycticoraxBKB15
                      |  `--Ardeola Boie 1822BKB15, CC10 [Ardeolini]
                      |       |--A. bacchus (Bonap. 1855) [=Buphus bacchus]M01
                      |       |--A. grayii (Sykes 1832) [=Ardea grayii; incl. Ardeola grayii phillipsi Scheer 1960]CS77
                      |       |--A. idaeJT12
                      |       |--A. ralloides (Scopoli 1769)M02 (see below for synonymy)
                      |       |--A. rufiventrisJT12
                      |       `--A. speciosaJT12
                         `--+--Bubulcus Bonaparte 1855BKB15, CC10 [Bubulcini]
                            |    `--*B. ibis (Linnaeus 1758) [=Ardea ibis, Ardeola ibis, Egretta ibis]CC10
                            |         |--B. i. ibisCC10 (see below for synonymy)
                            |         `--B. i. coromandus (Boddaert 1783)CC10 (see below for synonymy)
                            `--+--Casmerodius Gloger 1841 [=Cosmerodius Salvadori 1882]CC10
                               |    `--C. albus (Linnaeus 1758)CC10 (see below for synonymy)
                               |         |--C. a. albusCS77
                               |         `--‘Egretta alba’ melanorhynchos (Wagler 1827)CS77
                               `--Mesophoyx Sharpe 1894BKB15, CC10
                                    `--*M. intermedia (Wagler 1829) [=Ardea intermedia, Egretta intermedia]CC10
                                         |--M. i. intermediaCC10
                                         |--‘Egretta’ i. brachyrhyncha (Brehn 1854)CS77
                                         `--M. i. plumifera (Gould 1848) (see below for synonymy)CC10
Ardeidae incertae sedis:
  Pilherodius pileatusJT12
    |--G. goisagi (Temminck 1835)I92
    |--G. leuconotusJT12
    |--G. magnificusJT12
    `--G. melanolophus (Raffles 1822)I92
  Melanophoyx ardesiacaA61
  Dichromanassa rufescensA61
  Agamia agamiJT12
  Heterocnus cabanisiFS55
  Ardeagrandis Kuročkin & Ganea 1972M02
    `--*A. arborea Kuročkin & Ganea 1972M02
  Zonerodius heliosylusJT12
  Tigriornis Sharpe 1895B94
    `--T. leucolophaJT12
  Florida caeruleaS18
    |--A. flavicollisS89
    `--A. sturmii (Wagler 1827)CS77
  Gnotornis aramiellus Wetmore 1942M09
  ‘Anas’ basaltica Bayer 1883M02, M05
    |--H. caeruleaA61
    `--H. tricolorRN72
         |--H. t. tricolorS18
         `--H. t. ruficollisS18
  Leucophoyx thulaE52

Ardeola ralloides (Scopoli 1769)M02 [=Ardea ralloidesCS77; incl. A. ralloides paludivaga Clancy 1968CS77]

Bubulcus ibis coromandus (Boddaert 1783)CC10 [=Cancroma coromandaCC10, Ardea ibis coromandaCC10, Ardea coromandeliensis Stephens 1819CC10, Ardeola ibis coromandaL81, Bubulcus coromandensis Bonaparte 1855CC10, Egretta ibis coromandaCC10; incl. Ardea affinis Horsfield 1820CC10, Ardea bubulcus Gray & Gray 1846CC10, Ardea caboga Franklin 1832CC10, Ardea flavirostris Vieillot 1823CC10, Herodias flavirostrisCC10, Ardea russata Wagler 1827CC10]

Bubulcus ibis ibis (Linnaeus 1758)CC10 [incl. Ardea ruficrista Bonaparte 1855S66, CS77, Ardeola ibis seychellarum (Salomonsen 1934)L81, CS77]

Casmerodius albus (Linnaeus 1758)CC10 [=Ardea albaBKB15, Egretta albaCC10, Herodias albaK08; incl. Ardea egretta Gmelin 1789CC10, *Casmerodius albus egrettaCC10, A61, Egretta alba egrettaCS77]

Mesophoyx intermedia plumifera (Gould 1848) [=Herodias plumiferus, Ardea intermedia plumifera, Egretta intermedia plumifera]CC10

*Proardeola walkeri Harrison 1979M02 [=Ardeola walkeriM02, Proardea walkeriJM14; incl. Ardea formosa Milne-Edwards 1871 (n. n.)M02]

*Type species of generic name indicated


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