Saturday, July 15, 2017

Of Herons & Egrets

Birds: What is the difference between an egret and a heron?

Great Blue Heron - Ken Thomas  Great Egret in nuptial plumage - Eileen Cohen

from: Quora

Neil Kelley, Paleontologist, geologist, professor at Vanderbilt

It's an arbitrary distinction primarily based on superficial characteristics. "Heron" is a name typically applied to the entire bird family Ardeidae. "Egret" is a name applied to a variety of typically white herons, not all of which are closely related. For example: the Great Egret, Ardea alba, is a large white heron very closely related to the Great Blue Heron, Ardea herodius.

To make things more confusing, the Great Blue Heron occasionally occurs in a white color morph: Great Blue Herons
Likewise the heron genus Egretta includes a number of small to medium-sized species, some of which are called "egrets" and others are called "herons" depending on their color.

William Bezodis

Neil Kelley has already written a pretty good answer, but I would like to answer with the statement that taxonomically, there is no such thing as an egret.

For a group of organisms to be a valid taxonomic group, they must be monophyletic. The best way to explain what this means is to look at this diagram from Wikipedia:

If you think about this as a family tree or a tree of life, to be a monophyletic group (known as a clade) it needs to be possible to take the entire group and nothing else with a single cut. This is the idea of cladistics.

So applying this to the question of herons vs egrets then. Here you can see a ‘family tree’ (more correctly known as a cladogram) of the heron, egret, and bittern family, Ardeidae: Ardeidae

This is a valid group according to the criterion above (at least according to current taxonomic thinking) so is known as a taxon (plural taxa). Within this though, we can’t take a group that includes all herons or a group that includes all egrets, so neither is a separate clade, so according to the explanation above, they are not valid groups. Species commonly referred to as egrets are included in the genera Egretta, Bubulcus, and Ardea, but both Egretta and Ardea include species commonly called herons as well, so we would struggle to create even a polyphletic group of Egrets apart from just a list of species.

So to conclude, there is no such thing as an egret.

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To make things even more confusing, there is the Little Blue Heron, which is born white, and goes through a piebald stage on its way to its adult plumage.   photo: Tammy Karr

The adult looks like this: 

 

photo: Tammy Karr

And then there's the white phase of the Great Blue Heron...

 

 

So you see, you have every right to be confused.

photo - Jim Gilbert





photo: nigel/flickr

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