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  BIRDING AZORES

Untitled Document
  Snowy Egret Egretta thula or Little Egret Egretta garzetta?
 
 

The matter of field separation between these two very alike species has now and then been actualized, often in connection with one of the species occurring on the "wrong" side of the North Atlantic. For literature see for example Murphy 1992 and Massiah 1996.
   The fact that Little Egret Egretta garzetta is a rarity in North America, and Snowy Egret Egretta thula even being a little more rare in Europe, have still not rendered in any major interest in the difficulties involved when it comes to field identification. Still very few reliable field characters useful for identification have been discovered, and some of those most often referred to seem a little doubtful.
   In the Azores Little Egret is regular in small numbers, while Snowy Egret is rare but at least seen in a few occasions. Including 2006 there seem to be seven different birds, with the first ones in 1988. There have also been several sighting of "intermediate" coloured birds, and a question if hybrid herons occur have been asked more than once.

Field separation "from the book"
Except for mostly subtle characters like foraging behaviour, size, and "jizz" the main used criteria are the following:
1. Leg colour. Both species have yellow feet where the exact colour, intense, and demarcation from the leg differ depending on age and time of year. Above the feet leg colour differ in the "standard" birds in the way that garzetta has all black legs and thula also has more or less yellow (especially on back side) on legs.
2. Colour of lores. While lores (between eye and bill) are dull grey or grey-blue on garzetta, the colour is yellow on thula.
3. Head shape. A flatter head with white feathering reaching further out on the upper side of bill (equivalent to the feathering on under side of bill) in garzetta, is said to be different from thula which has less feathering on upper side of bill. This plus a peak of the crown further forward than in garzetta, gives thula a more "neat and round headed" appearance.
4. Breeding characters. When egrets start breeding the colour of lores as well as feet changes rapidly in booth species (generally more towards red and yellow), and the plumes become more developed (with two long lanceolate head plumes of garzetta, while thula shows a brushy crest of mixed short and long plume-like feathers). Unfortunately breeding characters are of no use in the concept of out of breeding season observations in the Azores, and will not be dealt with here.

Field separation "in reality"
As in many other near species pairs there is always the amount of overlap. A few extreme birds show mixed characters, and many characters are present in both species to a certain degree.
   What is then useful, and which characters or birds can we be sure of? In species so close to each others as these, we will probably have to accept a high number of individuals that we have to leave unlabelled. Hopefully further research will reveal new knowledge making us able to reconsider those observations put aside today.
1. Leg colour. The yellow colour on thula seems to be present in all ages, making the age determination from leg colour uncertain. Most classical is a black front, with a yellow line on the back of the leg, from about half the width down to just a line of yellow visible from behind. Often there is an extra large amount of yellow in the knee area, while the yellow slowly diminish and fades upwards the tibias. A few thula show more overall yellowish legs, where the black is reduced or faded and the yellow is more dull, making confusion possible even with Egretta gularis, and young Egretta caerulea. Also many (only adults?) thula show very dark legs with no, or a minimum of yellow, making legs looking identical as an ordinary garzetta. The classical leg colour (above the yellow well demarked feet) of garzetta is all black, or black with a grey-black to yellow-black tinge that in some lights gives reflections (especially in photos) looking like true yellow. At least on the Azores there are also a number of garzetta egrets (or at least supposed to be garzetta) that show more or less true yellow or yellow-green colour. These yellowish/greenish colours seem to appear in a number of different ways. From yellow on back tarsus, to yellow around knees, to an overall yellowish leg colour, and to a colouration very near a classical thula.
2. Colour of lores. Classical colour in thula is a rather dark, and very deep yellow, which covers lores and extends up and over the root of the upper mandible. For some younger birds, and apparently also for some faded adults in non breeding periods, the colour may also be soft and light yellow, with the covered area a little reduced. In all cases there is none or a very little difference in the colour of the eye and the lore, making the area uniformly yellow. In a classical garzetta the lores are grey or bluish grey, often with a very small area just in front of the eye in a soft yellow colour. At a little distance there is an obvious difference between the yellow eye and the greyish rather dark looking area between the eye ant the root of the bill. In garzetta there seem to be no birds (?) with the dark deep yellow colouration, neither no yellow colour extending up and over the root of the upper mandible.
3. Head shape. I have checked the head form as well as the extension of the white feathering around the bill in the field, as well as in between 500-1000 photographs, but I do not think these characters (if there really are any) are of any use. It seems to be a total overlap, and the only obvious thing is the amount of white feathering towards the upper mandible. But this is entirely a product of thula showing more yellow there, thus making all the difference in feathering, and also to some extent, the (maybe) small difference in head shape. The average thula is in many aspects a smaller, neater and more "round headed" bird, but all these are very subtle characters which differs with the birds mood and actions, the weather etc. For very experienced birdwatchers, daily in contact with both species, some of these characters are probably useful. But for the average birdwatcher, and for checking out still photos, this is not the case.

Conclusion
With the knowledge we have today, we will probably have to leave a number of small white egrets undefined. The colour of the lores seems most important, and a small egret with a large dark deep yellow area extending up and above the upper mandible should mean a thula. If the bird also shows much yellow on legs, preferable as a broad line on the backside of legs, I think we could be certain of this egret being a Snowy. A bird with all dark legs, and grey to blue-grey colour on lores, well demarked from a contrasting yellow eye should be a certain garzetta. Intermediate birds showing more or less yellow on legs, combined with smaller areas of soft (light) yellow on lores will probably as for now be judged as undefined garzetta /thula birds.
   A number of birds that sometime have been claimed to be Egretta thula (or just possible Egretta thula), Egretta garzetta or possible hybrids are now in the undefined category "Egretta thula/garzetta". Maybe they later on can be reconsidered and given a certain classification. Some examples of these birds are shown here.


Records of Snowy Egret in the Azores
1988-10-10 to 1988-10-11. 2 birds at Santa Cruz, Flores.
2001-11-18 to 2002-01-12. 1 at Horta, Faial.
2003-11-13 to 2003-11-27. 1 at Horta, Faial (with rather dark legs).
2003-12-21 to at least 2005-02-27. 1 at Horta, Faial (not the same as in Nov. 2003).
2004-10-26. 1 at Praia da Vitória, Terceira.
2006-11-03 to 2006-11-15. 1 at Fajã Grande, Flores.


References:
Massiah, E. 1996. Identification of Snowy Egret and Little Egret. Birding World, Vol. 9: 434-444.
Murphy, W. L. 1992. Notes on the Occurrence of the Little Egret (Egretta garzetta) in the Americas, with Reference to Other Palearctic Vagrants. Colonial Waterbirds, Vol. 15: 113-123.


Staffan Rodebrand, Sweden

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2006-11-03. Snowy Egret Egretta thula at Faj Grande, Flores. Note how the deep and dark yellow colour on the lores continue up and over the upper mandible. Photo: Staffan Rodebrand

2000-11-11. This bird at Mosteiros, So Miguel showed lots of clear yellow on legs, especially around knees. The lores were to some parts yellow. But not dark yellow, and lores were also greyish towards bill. Photographed and videotaped but unfortunately no good photos. Photo: Bosse Carlsson

2004-04-05 Horta, Faial. Classical Snowy Egret Egretta thula. Note dark deep yellow on lores going up over bill, and yellow stripes on back side of legs.
Photo: Joo Quaresma


2006-01-31 Santa Cruz, Flores. Typical Little Egret Egretta garzetta.. Note dark legs and greyish tone at the base of the bill. In garzetta the lores are often greyish towards the bill, but with a smaller soft and light yellow area near the eye. Note also that the yellow feet most often are coloured in the same way as the lores - garzetta then often having somewhat lighter feet than thula.
Photo: Staffan Rodebrand


2006-11-12. Mosteiros, So Miguel. In previous years there have been several small white egrets on So Miguel with rather much yellow on legs. This birds show much yellow as back line on legs, widening around knees. But the lores are mixed coloured with soft yellow near the eye, and elsewhere grey or greyish blue. Videograb: Johan Lorentzon

2006-11-15. Mosteiros, So Miguel. Probably the same bird as above. In Jan/Feb 2007 "yellowlegged" small white egrets were seen both at Mosteiros and Ponta Delgada but they shoved mixed coloures on lores where the yellow were of the more light and soft version. Photo: Nico de Vries

2006-11-12. One of probably at least four small white egrets at Faj Grande Flores. On the third of Nov. two birds turned up at Fajã Grande, one a clear thula that stayed on western Flores up to at least the 15th of November. This bird was together with a second "yellowlegged" bird which unfortunately neither were studied much in detail, nor photographed. Later a typical garzetta were seen together with the thula, but also the individual photographed here. With no yellow of legs this one should normally go for a typical garzetta, unless the lores were checked. These are yellow "all over" and the colour is rather intense and dark.
Photo: Staffan Rodebrand


2004-10-27. Cabo da Praia Terceira. One of several small white egrets present on Terceira this autumn (also including more typical thula and garzetta). This one had rather much yellow on lores, but the colour is too light and soft. The legs had greenish yellow streaks on back side - widening around knees.
Photo: Staffan Rodebrand


2004-10-13. St. Matheus, Terceira. A rather chunky, thick-legged bird with overall much yellow or green-yellow on legs. Lores mostly greyish, with some soft yellow near the eye - a rather common lore colour in garzetta.
Photo: L. J. Salaverri


   
 
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