AERC (Association of European Records and Rarities Committees) TAC's (Taxonomic Advisory Committee's) Taxonomic Recommendations - 1st December 2003 (
www.aerc.eu/DOCS/AERCTAC.pdf):
"
Great White Egret Egretta alba proposed to become
Casmerodius albus
STC Although Voous (1973) preferred to call this species
Ardea alba, he maintained
Egretta alba in his
List of Recent Holarctic Bird Species. The inclusion of this species in
Ardea is supported by DNA-DNA hybridisation data (Payne & Risley 1976, Sheldon 1987b, Sheldon et al. 1995 and Sibley & Monroe 1990); Great White Egret is more closely related to
Ardea than to
Egretta. It was listed as
Ardea alba by Mayr and Cottrell (1979,
Peters’ Check-list of Birds of the World, Vol. 1, 2nd ed., pp 203-204). The relationships among the races are not clear.
A. a. modesta may be a separate species, but extensive comparisons among all forms have not been done. Accepted as
Ardea alba by AOU 1995 and in BOURC (1996). The CSNA and A.J. Helbig, however, preferred to place Great White Egret in the genus
Casmerodius (Sangster et al. 1997; A.J. Helbig in litt.). Phylogenetic analyses based on DNA-DNA hybridisation indicate that Great White Egret is not closely related to the
Egretta clade and instead suggest a closer relationship with
Bubulcus and
Ardea. However, given the unresolved relationships between
Ardea, Great White Egret, Intermediate Egret
Mesophoyx intermedia and Cattle Egret
Bubulcus ibis, the CSNA believes that the inclusion of Great White Egret in
Ardea (e.g. AOU 1995, BOURC 1997) is premature. Until the relationships of Great White Egret are better understood, the CSNA prefers to place it in a monotypic genus
Casmerodius (cf. Inskipp et al. 1996) (Sangster et al. 1997). A.J. Helbig (in litt.) commented on his personal point of view: ‘Molecular studies confirm two monophyletic families (Sheldon et al. 2000). Great White Egret is equidistant from
Ardea and
Bubulcus, thus retained in a separate genus (
Casmerodius). Relationships of Intermediate Egret (
Mesophoyx / Egretta) are unknown.’ It should be noted, however, that in the field,
intermedia shows intermediate features between
Bubulcus and
Casmerodius, suggesting a position in between these two taxa rather than in
Egretta. If Great White Egret were to be placed in
Ardea, the relationships of
Bubulcus and
Mesophoyx would need to be re-examined as well. In the field, Intermediate Egret shows more similarities to Cattle Egret and Great White Egret than to any of the
Egretta species (G. De Smet, pers. observations). Although it is clear that the status quo (retaining
intermedia and
alba in
Egretta) is wrong, this case clearly shows the need of
Guidelines for assigning generic status and consultation among TCs before adopting generic changes. The rule of ‘monophyly’ seems to be applied in various ways by different committees. In addition, more research on the genetic relationships of
intermedia is crucial, before a satisfactory decision can be reached. With two rejections for each option (
Casmerodius albus or
Ardea alba) only an arbitrary decision is possible. There is agreement that Great White Egret must leave
Egretta but no consensus that it must enter
Ardea or
Casmerodius. Given the uncertainty about the relationships of Intermediate Egret and the possible implications for Cattle Egret, a cautious approach is needed. Therefore, Great White Egret is provisionally placed in
Casmerodius albus until its relationships are resolved."
Current opinions include:
Ardea: H&M, Clements, IOC, AOU, ABA, BOURC, OSME
Casmerodius: BirdLife, AERC, DBA/CSNA, OBC
Egretta: ABC
