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Great Egret - Egretta or Ardea ? (1 Viewer)

Astrokev

Well-known member
I would be grateful if someone could help me understand the correct taxonomic classification of the Great Egret.

Collins Bird Guide lists the european species as Egretta alba.
Sibley guide to Birds of North America lists the US species as Ardea alba.

I was under the impression that they belonged to the same genus and were only split at the sub-spp level.

Please could someone clarify the correct nomenclature?

Many thanks
Kev
 

rob stoff

Well-known member
there is long standing confusion about which genus Great Egret should be in, i.e whether its an egret or a heron, as well as Ardea and Egretta its sometimes placed in the genus Casmerodius as well!

All the same species though, at least at the moment

Rob
 

Xenospiza

Distracted
Supporter
On the basis of its DNA, Great Egret is close to Ardea, and not to Egretta: Egretta alba is (now known to be) wrong.

The use of Casmerodius can be defended on the basis that its relationship with other Ardea species is not certain.
 

Richard Klim

-------------------------
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
 
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l_raty

laurent raty
[...] Relationships of Intermediate Egret (Mesophoyx / Egretta) are unknown.' [...]

Well, we know a little bit more on this, now - and it's central to the issue too. Two recent published genetic studies have included great white, intermediate and cattle egrets, as well as representatives of Ardea. One is a Chinese study that used sequences of the 12s-rRNA gene: http://www.actazool.org/paperdetail...er=2&bgpage=205&endpage=210&year=2003&month=4 ; the other is a Korean work based on COI sequences ("DNA barcodes"): http://www.ksmb.or.kr/storage/journal/MnC/22_3/1040/articlefile/article.pdf. In both cases, intermediate egret appeared as the closest relative of great white egret.

IOW, all the authorities that place the great white egret in Ardea while leaving the intermediate egret out of it are most likely wrong in some way - either their circumscription of Ardea is too broad, or it is too restricted.

Note that in their last monograph, Hancock & Cushlan (2005 : http://www.oup.com/uk/catalogue/?ci=9780198549819 ) extended Ardea to make it include the entire group, including great white, intermediate AND cattle egrets. This solves all the phylogenetic problems, because these are all due to uncertainties in the relationships among sub-parts of this group, while the group itself is extremely strongly supported. On the other hand, most authors have up to now regarded the cattle egret as morphologically too divergent to be included in Ardea.
 

Gentoo

Guest
Thanks for that info, I still have some stuff to learn about herons although I have little trouble identifying most of what I see.

Is there more than one American race? I see some that are almost as large as Great Blue Herons sometimes. Most seem to be about a third smaller but a few are huge.
 

Richard Klim

-------------------------
Is there more than one American race? I see some that are almost as large as Great Blue Herons sometimes. Most seem to be about a third smaller but a few are huge.

The only American race is egretta, 'American Great Egret'.

Larger white examples in S Florida might be Ardea herodias occidentalis, 'Great White Heron' (the white form of Great Blue Heron).
 
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Gentoo

Guest
The only American race is egretta, 'American Great Egret'.

But large white birds in S Florida might be Ardea herodias occidentalis, 'Great White Heron' (the white form of Great Blue Heron).

Thanks, I saw one here in San Diego a while ago that was distinctly larger than the other ones around it. I never got them together though to get a picture for comparison.
 
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