Dimorphic vs. Little Egret (Zanzibar) (1 Viewer)

[Corotauria]

Hi guys,

Few weeks ago I visited Zanzibar, Tanzania. Although it was mostly a relaxing holiday, we also spend some time birding. Along the coast, lots of egrets were present at low tide. Only at the part near our resort, I would say around 20-40 each day. Both Dimorphic and Little Egret should occur (although I don't really know the status of Dimorphic Egret in december), and we had some difficulty determine most of the egrets.

According to our field guide, both species are best told apart by the feet: "black legs with clear yellow feet" by Little Egret, and "extending yellow a little up front of the black legs" with Dimorphic Egret. By all birds by which we have seen the feet properly, the legs were black, and the feet clear yellow, as one would expect to see by Little Egret. When stopping there, all egrets we have seen should be Little.

But, literature says a dark morph is rare by Little, common by Dimorphic Egret. Of all Egrets we have seen, about one third was a dark morph. Some including the white or buffy wing patches (in flight) one would expect by Dimorphic Egret. Assuming that maybe 50 percent of all present Dimorphic Egrets are dark morphs, then most egrets we have seen should be Dimorphic!

As I expect that it is more likely that Dimorphic Egret have clear yellow feet (not extending up the legs), then dark morphs Little Egret are common on Zanzibar, I am wandering what is in fact diagnostic to distinguish both species...??? Anyone good advices on that one?

Most curious off course (meaning, if my assumption is correct) how to tell by white morphs with clear yellow feet, if it is a Dimorphic or a Little Egret...?

I will add some photo's later on, but hopefully someone can help me with this interesting question? Thanks!

All the best.
Rick

 

[rockfowl]

Aren't they really just subspecies - http://ibc.lynxeds.com/species/little-egret-egretta-garzetta?

From Heron Conservation - " In dimorpha dark individuals are blackish, slightly lighter than gularis, usually with white throats and white wing patches on the carpel joint and sometimes with white speckles. Rare intermediate birds are paler, with mixed dark and light feathers. Light individuals are white occasionally with stray dark feathers. Nonbreeding lores are yellow. The bill and legs are jet black, and the feet are yellow. The bill in some populations is thicker than that of garzetta, although this is not universally the case such as in coastal east Africa (Baker and Baker in prep.). In courtship, lores and feet are red returning to yellow.
"

 

[Corotauria]

By some considered as subspecies, by some as species. It doesn't matter to me, the question stays the same... ;-)

The dark morphs I have seen fits in perfectly with the description you gave me.
The "The bill in some populations is thicker than that of garzetta, although this is not universally the case such as in coastal east Africa (Baker and Baker in prep.)." isn't really helpfull though (meaning the text, not you finding the text, gratefull for that!).

In an other tread I have read dimorpha should have a longer and thinner neck? I don't see that on photo's though. I will add a first photo soon.

Thnks!

 

[Corotauria]

A first photo. I have no problem calling this garzetta.

 

[njlarsen]

From Mark's post in this thread regarding dimorpha:

Nonbreeding lores are yellow

should be something to really look for in your photos

Niels

 

[Corotauria]

Thanks for your reply Niels and pointing that out to me.
I will add some photo's of a grey bird later on, with grey lores. Also all white morphs I have photographed have grey lores instead of yellow or red (breeding season is coming up I presume...?).

Quotes from Birds of East Africa about the lores, seems that these are not as diagnostic is the text from Mark's post:

Little Egret

Lores are usually blue-grey, but may turn yellowish or orange in br birds.

Dimorphic Egret

Lores are usually grey, but may be yellow, and turn pinkish in br birds (as do feet)

 

[Corotauria]

I have added some new photo's to my website. Two different birds, a white morph and a dark morph. As said above, both with grey lores.

In an other tread I have read dimorpha should have a longer and thinner neck?

In contrary to what I said above, I think I do see some differences in proportions of the neck. See both photo's I added to this message. Both birds have their necks stretched, but the dark morph seems to have a much thinner and especially longer neck then the added white morph. Seems to me that the white one should be garzetta, while the dark one (although clear cut of yellow feet) is dimorpha. Anyone?

 

[Corotauria]

And the second photo.

 

[Tib78]

Rare intermediate birds are paler, with mixed dark and light feathers."

Nice to see that 'intermediate birds' are mentionned. I had always been wondering whether they were young dark morph; worn birds or just paler birds. However I wouldn't say they are rare. Just the least represented morph along the coast. See attached photo of a small flocks with the 3 morphs.

I have attached 2 more shots that might be of interest:
-a dark morph bird on the tide line, not sure how one would qualify the color of the lores?
-a photo that I had already posted before: 3 birds; the white bird showing a black primary coverts and apparently yellow lores; one of the dark bird showing some white on the greater primary coverts. This shot illustrates the propensity of the taxon to appear "pied".

Edit: all photos taken in/near Dar es salaam; end of september/begining of october

 

[tconzemi]

Interesting thread
I had the same dilemma back in 2005, so what would you make out of this one
pied but blue lores and feet as Little Egret!?? :brains:

 

[rockfowl]

They freely hybridise Tom, so adding to the confusion.

 

[Corotauria]

Thanks for adding some more photo's.
@ Tib78: Do you consider your's all as Dimorphic?

The black spots and primaries and secondaries are mentioned as charasteristic of white morph dimorpha. Typical that all these birds have the yellow feet of garzetta.

 

[Tib78]

@ Tib78: Do you consider your's all as Dimorphic?

I do, but I am open to suggestion.
See also: http://www.birdforum.net/showthread.php?t=217270

 

[Corotauria]

From the tread your linked:

...and welcome to the muddy waters of Egretta identification and taxonomy.

Generally speaking, it seems safer to consider any 'black' Egretta along the Tanzanian coast (including Zanzibar) as an E.dimorpha = Dimorphic Egret (let alone Black Egret, which is very different and easy to ID). But things change as you reach the Kenyan coast, because Western-Reef Heron must be taken into consideration

I imagine you were considering Little Egret because of the 'clear-cut yellow feet' as described in Stenvenson and Fanshawe's, I can however assure you that this is by no mean an ID feature (otherwise it would mean that the Tanzanian Coast is full of dark morph Little Egrets...).
From my own experience, Dimorphic appears a bit longer billed than Little, the bill is also deeper based with a slightly drooping tip (all this rather subtle...) and in my opinion, your bird fits perfectly.

To illustrate the serious ID problems caused by the genus Egretta, I have attached a shot taken near Dar-es-Salaam. At first, I thought the white bird might be a Little Egret because the bill looks noticeably thinner and straighter than the bills of the dark birds (not a photographic artefact as I had the same impression in the field) but when reviewing my pictures, I noticed that one of the wing-covets near the wrist is black....and I know that dark Dimorphic egrets commonly show a few white feathers in this area and vice-versa...so I don't know exactly what this bird is, but I think it's probably a white Dimorphic.

What do you mean with "a slightly drooping tip"?
Do you mean to bill get's a bit paler to the tip?

 

[tconzemi]

From the tread your linked:



What do you mean with "a slightly drooping tip"?
Do you mean to bill get's a bit paler to the tip?

no, the tip of the bill is very slightly turned downwards

 

[Corotauria]

Thanks! I don't see it on photo's though (it's me, I know).

Attached another photo of the same Dimorphic as above.
Just the be complete in this topic.

 

[Corotauria]

So, next one. The difficult ones, a white morph.
What would you call this one? Dimorphic or Little? And why?