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.
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.
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
to the Archive page»
Snowy Egret Egretta thula at Fajã 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, São 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: João Quaresma
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
Mosteiros, São Miguel. In previous years there have been several small white egrets
on Säo 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:
Mosteiros, São 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
One of probably at least four small white egrets at Fajã 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.
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
Photo: Staffan Rodebrand
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.