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Re: Caspian vs. Royal Tern
- To: CarolinaBirds <carolinabirds@duke.edu>
- Subject: Re: Caspian vs. Royal Tern
- From: Michal Skakuj <mskakuj@nc.rr.com>
- Date: Fri, 25 Apr 2003 18:42:31 -0400
- Delivered-to: pardo@metalab.unc.edu
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Hi,
Tern comments,
Shantanu Phukan wrote:
So, my question is is there much bill color variation in Royal terns, with
some of them inclined towards red rather than orange. Or is the red such a
definite diagnosic mark that its presence (despite no size difference)
would clinch this as a Caspian.
The coloration of bare parts of birds vary a lot according to particular
season. These colors are usually more bright in breeding season or just
during a short period of courtship (like in Cattle Egret when for a week
or so birds have deep red billl and even legs, comparing to usually
yellow). More hormones in the blood more colors they have (and not only
birds ;-). In additional that may vary with "bird's mood" and condition.
Week and sick birds show tendency to have more dull coloration of bare
parts as well as feathers. (contrary to some handsome and proud
male...). So, I wouldn't be surprise to see Royal Tern (especially very
macho male) with more reddish bill than the others. The color is
described as "orange to orange-red, paler and yellower from July" (Olsen
and Larson 1995). Personally I never use colors to correct ID of Gulls,
Tern, Shorebirds etc., more important are structural features (size and
proportions) together with behavioral ones, that what some called
"jizz". So, if you see tern which is Royal in size and structure then
it most probably IS Royal despite of strange bill/legs color. Caspian is
"a size bigger creature" just slightly smaller than American Herring
Gull, with much more bigger bill. In addition on underwing outer
primaries are distincly darker than other flight feathers (large
blackish patch on outer underwing) whereas Royal has distinc blackish
(sometimes very diffuse) trailing edge to the outer primaries. However
from above outer promaries are DARKER than the others in Royal and more
or less same grey color in Caspian.
THe second question is regardng Sandwich vs. Gull Billed Tern. Yes, I know
that Gull Billed Terns have a shorter and thicker bill; however, when one
sees a lone tern with nothing to compare it to it is difficult to decide
if the bill is thick enough or not and I have now several times decided
that a tern was Gull billed only to then finally see the little yellow tip
as it turns and catches the light. So is there any other clue besides the
lenght and thicknessof the bill. If, for example, one sees a Gull
Billed/Sandwich Tern over the ocean can one definitly rule out the GUll
Billed since they are supposed to feed on mudflats and grassy fields?
Again, colors are in most cases additional features for Terns-Gulls ID
(being very important in immature Gulls especially but it is a different
story). Gull-billed Tern comparing to Sandwich is longer legged, bigger
(more rounded) headed (ones could say even bigger eyed bird) with
distinctly shorter, heavier base bill. In flight Gull-billed is more
heavy-bodied bird with distinct (heavy) bill (and all head actually).
Flying Sandwich has slimmer body emphasized by long and narrow bill
which make the bird looks more "very pointed nose silhouette". In
addition Gull-billed has less slender wings and they are not so
distinctly "banded or curved" in carpal join as in case of Sandwich.
There are also good color features of flying birds. Gull-billed has
primaries rather uniformly gray with diffuse blackish tips to ca 5
outermost primaries. That is seen as darker so diffuse trailing edge to
the outer primaries. In Sandwich (due to different moulting strategy)
4-6 outer primaries are older than the others so they are more wearied
out means they are DARKER (especially late Summer). That is well
visible as contrast between lighter inner and darker outer primaries
(seen well both sides upper and under and even against the sun). The
other feature like gray rump of Gull-billed comparing to white of
Sandwich are visible from rather close distance. However for me
Sandwich looks more whitish whereas Gull-billed more grayish on mantle
and upper wings.
If you see Gull-billed/Sandwich flying constantly just above the grass
or along some ditch that is a good feature of Gull-billed but if you see
the same mystery bird just over the ocean that means not much. However
there are some subtle fly-action differences (jizz again) which help to
ID lonely tern even from far distance. However I have to say it is
impossible to ID EVERY Tern flying, 70% effectiveness is a very good
anyway.
Hope that will help however the best is to go and discus some real birds
being seen in a scope....
Mike
--
************************************************
Michal Skakuj Ph.D.
4600 University Drive apt. 1312
Durham, NC 27707
phone: 919 402 9961
mobile phone: 919 599 3040