Heron - Taxonomy and Systematics

Taxonomy and Systematics

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. 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, which are (from the most primitive to the most advanced):

• tiger herons and the boatbill
• bitterns
• day-herons and egrets, and night-herons

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.

Recent DNA evidence suggests that this family belongs to the Pelecaniformes. In response to these findings, the International Ornithological Congress (IOC) recently reclassified Ardeidae and their sister taxa Threskiornithidae under the order Pelecaniformes instead of the previous order of Ciconiiformes.

Subfamily Tigrisomatinae

• Genus Cochlearius — Boat-billed Heron
• Genus Tigrisoma — typical tiger herons (3 species)
• Genus Tigriornis — White-crested Tiger Heron
• Genus Zonerodius — Forest Bittern

Subfamily Botaurinae

• Genus Zebrilus — Zigzag Heron
• Genus Ixobrychus — small bitterns (8 living species, 1 recently extinct)
• Genus Botaurus — large bitterns (4 species)

Subfamily Ardeinae

• Genus Zeltornis (fossil)
• Genus Nycticorax — typical night herons (2 living species, 4 recently extinct; includes Nyctanassa)
• Genus Nyctanassa — American night herons (1 living species, 1 recently extinct)
• Genus Gorsachius — Asian and African night herons (4 species)
• Genus Butorides — green-backed herons (3 species; sometimes included in Ardea)
• Genus Agamia — Agami Heron
• Genus Pilherodius — Capped Heron
• Genus Ardeola — pond herons (6 species)
• Genus Bubulcus — cattle egrets (1-2 species, sometimes included in Ardea)
• Genus Proardea — (fossil)
• Genus Ardea — typical herons (11-17 species)
• Genus Syrigma — Whistling Heron
• Genus Egretta — typical egrets (7-13 species)
• Genus Mesophoyx — Intermediate Egret
• Genus undetermined
  • Easter Island Heron, Ardeidae gen. et sp. indet. (prehistoric)

Fossil herons of unresolved affiliations:

• Calcardea (Paleocene)
• Xenerodiops (Early Oligocene of Fayyum, Egypt)
• "Anas" basaltica (Late Oligocene of "Warnsdorf", Czechia)
• Ardeagradis
• Proardeola — possibly same as Proardea

Other prehistoric and fossil species are included in the respective genus accounts