Hola,
Refreshing the dark-billed Great Egret topic, contained below is a link to
more images by Pat Mann, as well as comments by Marshall Iliff which he asked
me to forward to the various lists. Also, there may be more images posted to
Bill Hubick's site within a day or so.
New images by Pat Mann:
_http://www.flickr.com/photos/patmann/2599884413/in/photostream/_
(http://www.flickr.com/photos/patmann/2599884413/in/photostream/)
Images hosted at Bill Hubick's site:
_http://www.flickr.com/photos/patmann/2599884413/in/photostream/_
(http://www.flickr.com/photos/patmann/2599884413/in/photostream/)
Images at Larry Meade's site:
_http://www.uberlarry.smugmug.com/gallery/2498169_rgafW/1/303652728_xnXu8#3036
54690_MoG5E_
(http://www.uberlarry.smugmug.com/gallery/2498169_rgafW/1/303652728_xnXu8#303654690_MoG5E)
Comments from Marshall Iliff:
Now that I am back from a busy work week, I have had a little more time to
think about the black-billed Great Egret at Chincoteague. In short, I think
it is most likely E. a. melanorhyncha of Africa, but still feel that an
aberrant E. a. alba should be eliminated.
I am still missing some key references (Birds of the Western Palearctic, for
example), but here are some new thoughts. Below my thoughts is the
subspecies account from Birds of North America Online. Below I consider the
field marks and probability of two black-billed Old World subspecies:
Widespread northern E. a. alba and Africa E. a. melanorhyncha; I follow
Clements (2007) is using E. a. melanorhyncha, rather than melanorhynchos
from BNA.
SUBSPECIES ID
Based on the account in BNA, note that E. a. alba is LARGER than E. a.
egretta. The only written account of the Chincoteague bird I've yet seen
(reporting it as Reddish Egret) mentioned "nor was it as large as other
Great Egrets nearby." If so, perhaps this observation eliminates E. a. alba
and implicates E. a. melanorhyncha. A. a. melanorhyncha is "similar to
egretta" in size (BNA). A major question then is whether this bird is REALLY
smaller, or was it just reported as smaller when the observers believed it
was a Reddish Egret?
The top photos here (http://www.billhubick.com/others/va_egret.html) appear
to show tibia that are black to the base. According the the BNA, E. a. alba
and A. a. melanorhyncha have all black legs while those of alba and modesta
are pale at the base (as illustrated by Mullarney et al.). I would think
that we would see the pale if it was present and this seems to be a strong
character indicating that the bird is not E. a. alba.
The lores on this bird appear to be dull gray-olive in most photos. Loral
color of E. a. melanorhyncha is described and illustrated as lime-green in
high condition by Sinclair & Ryan (2003; Birds of Africa) and emerald green
in high condition and olive-green in non-breeding condition by Borrow &
Demey (2001; Birds of West Africa). This latter description appears to match
the Chincoteague bird. I do not know if North American birds ever shows
lores of this color--the lores are lime-green in high condition and yellow
in non-breeding condition, but I do not know about intermediate stages. The
BNA says: Color changes in soft parts vary among populations and have been
used in the field to identify subspecies (see Hancock, J. and J. A. Kushlan.
1984. The herons hand-book. Harper and Row, New York.) It seems to me that
this is one of the important questions to investigate further.
GEOGRAPHICAL PROBABILITY
I am willing to essentially rule out Asian E. a. modesta based on
probability; although East Asian shorebirds, gulls, Long-billed Murrelet,
and even a few passerines have vagrancy patterns that track across Canada
and the United States as far as the East Coast, this is not true of any
herons. In fact, all Asian heron vagrants that have reached the New World
have occurred ONLY on the Aleutians, including Chinese Pond-Heron, Chinese
Egret, Little Egret, Intermediate Egret, Gray Heron, Yellow Bittern, and
Asian taxa of Cattle Egret, Great Egret, and Black-crowned Night-Heron (an
impressive list!); no herons of Asian origin have been confirmed from
mainland Alaska or anywhere else in mainland North America.
The vagrancy pattern for Eurasian herons in Eastern North America appears to
center on the equatorial trade winds zone. Many Palearctic birds (including
Alpine Swift, Spotted Crake, White Stork, Eurasian Kestrel, Collared
Pratincole, and other more "standard" Eurasian shorebirds, gulls, terns,
Common Cuckoo etc.) have been recorded from the Caribbean, but foremost
among these are herons. Cattle Egret reached the New World by crossing in
this zone, colonizing eastern South America and the Caribbean and spreading
north from there. Little Egret and Gray Heron are both in the process of
colonizing the Caribbean, albeit more slowly. There are also records in the
Caribbean/eastern South America for Western Reef-Heron, Little Bittern, and
Purple Heron. Regardless of subspecies, I would suggest that the
Chincoteague Great Egret probably reached the New World via this route.
It also seems to be that the North Atlantic may be another vagrancy route,
since Gray Heron records from Newfoundland at sea off Newfoundland suggest
that birds were arriving directly across the North Atlantic. However, given
that Little Egret is uncommon in the UK and has strayed to Iceland just 9
times (through 2002; http://www.hi.is/~yannk/status_egrgar.html), I
personally believe that Newfoundland/Nova Scotia/New England records of
Little Egret may be birds that have crossed around the equator and migrated
north with other herons. Along the same lines, Western Reef-Heron is
unrecorded in the British Isles, but has occurred in the Northeast on at
least two separate occasions (Massachusetts 1983 and Newfoundland-Nova
Scotia-New Hampshire-Maine-New York in 2006-07). I'd argue that Western
Reef-Heron has reached the New World by crossing in the Caribbean and moving
north from there, and would further argue that the same is true for Little
Egret. To return to the Great Egret, I note that Iceland had only two
records of Great Egret through 2002.
Given a choice between E. a. egretta and the African E. a. melanorhyncha, I
initially thought E. a. alba would be vastly more likely, as it is
migratory, winters as far south as Africa, and would be likely to be
displaced off of western Africa on its northward to southward migrations.
Given the Caribbean records of Western Reef-Heron, which is strictly coastal
in West Africa and essentially non-migratory, E. a. melanorhyncha becomes
more likely and at least a reasonable option. (Given that thinking, perhaps
Goliath and Black-headed Herons are not out of the question for North
America and Intermediate Egret certainly isn't). In the end, I tend to think
either subspecies is equally possible, although the migratory nature of E.
a. alba still gives that form the edge in my mind.
THINGS TO CHECK
Observers that see and photograph this egret could help this process by
focusing their attention on a few things:
1) Carefully compare the size with surrounding Great Egrets
2) Carefully study the loral color of this bird in good light and describe
it relative to other Great Egrets at Chincoteague
3) Carefully check for any other characters that might differ between this
bird and surrounding Great Egrets. Does the gape line extend farther behind
the eye? Are there any bill structure differences? Do the plumes coming off
the back of the bird appear longer in the black-billed bird or shorter?
4) If anyone notices a feather fall off the bird it would be worth
collecting for genetic analysis. Feathers collected in this fashion provided
some genetic information on the Maryland Kelp Gull.
This is a case where detailed descriptions can be very useful in assessing
field marks (like relative size) that are hard to capture in photos and it
would be nice to see some truly detailed descriptions of this bird.
Best,
Marshall Iliff
-----------------------
From Birds of North America Online
(http://bna.birds.cornell.edu/bna/species/570/articles/systematics)
[requires subscription]
(Recommended Citation: Mccrimmon, Jr., Donald A., John C. Ogden and G.
Thomas Bancroft. 2001. Great Egret (Ardea alba), The Birds of North America
Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from
the Birds of North America Online:
http://bna.birds.cornell.edu/bna/species/570)
Subspecies
Four subspecies recognized following Payne 1979; ranges disjunct except
between modesta and nominate alba in e. Asia. Subspecies based on size
(mainly average differences in wing length) and color of bare parts
(especially extent of black on bill and red on legs in breeding adult).
Measurements below from Marchant and Higgins 1990 .
A. a. egretta Gmelin, 1789: Breeds over entire range in the Americas (see
Distribution, above). Small, with average wing length of male about 383 mm;
bill of breeding adults orange-yellow, with black along culmen; tibia black.
A. a. melanorhynchos Wagler, 1827: Mainly resident south of the Sahara in
Africa, from Senegal and Sudan south to Cape Province; also on Madagascar.
Small (similar to egretta); most of bill becomes black in breeding adult;
tibia black.
A. a. alba Linnaeus, 1758: Breeds in scattered localities across central and
se. Europe and across much of temperate Asia to n. Japan; winters to central
Africa, Persian Gulf, n. India, s. Korea, and s. China. Large (438-451 mm);
bill becomes mostly blackish in breeding birds; tibia, especially basally,
dull yellowish becoming reddish in breeding birds. Populations in Japan and
nearby areas may be intermediate in size toward modesta (Amadon and
Woolfenden 1952).
A. a. modesta Gray, 1831: Breeds in se. Asia from Pakistan and India east
and from s. Japan south through Indonesia, Australia, and New Zealand.
Population on New Zealand sometimes recognized as separate subspecies,
maoriana . Small, but Australian and New Zealand populations average larger
than those in India and China (wing length of male 376 mm versus 361.5 mm);
bill and legs similar to nominate alba.
--
-------------------------------------------------
Marshall J. Iliff
West Roxbury, MA
miliff AT aol.com
-------------------------------------------------
eBird/AKN Project Leader
Cornell Lab of Ornithology
159 Sapsucker Woods Rd.
Ithaca, NY 14850
http://www.ebird.org
http://www.avianknowledge.net
-------------------------------------------------
---------------------------------
Todd Michael Day
Jeffersonton, Virginia
Culpeper County, USA
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