MD Slaty-backed Gull photos now on the web!

Miliff@aol.com
Fri, 5 Mar 1999 18:52:08 EST


Hello all,

I wanted to let everyone know that the best of my photos of the probable
Slaty-backed Gull from Conowingo Dam are now posted on the Maryland
Ornithological Society (M.O.S.) webpage 

http://www.mdbirds.org/rarebirds.html

Many thanks to Jim Stasz for hurrying to get these images scanned in and to
Fran Saunders for graciously posting them to the M.O.S. webpage.

Below I have copied the comments and photo captions that I hope will soon be
posted to the website.  You may wish to refer to them if you are looking at
the photos tonight or if it takes some time for the comments to be integrated
with the photos on the website.  I hope soon to post Maryland photos of a
_possible_ European Herring Gull, the Kelp Gull, and a Harris's Sparrow (just
for kicks) to this website as well.      

I will be interested in any comments on this bird.

Best,

Marshall J. Iliff
miliff@aol.com
Annapolis, MD

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History of the bird:
	This gull was first noted by Rick Blom, Dave Czaplak and Mary Ann Todd on
Saturday, February 6.  It was observed by a number of Maryland birders the
next day, and over the next week it was seen by hundreds.  It appeared to be
using Conowingo Dam as a rest stop, as it was usually seen preening and
bathing here and was only seen in the morning (7:00 a.m. to 10:00 a.m.) and
evening (3:00 p.m. to 5:45 p.m.).  When it was watched departing the Dam in
the morning, it was seen flying upriver towards Pennsylvania, and when watched
leaving the dam at night it headed downriver, presumably to the roost at Havre
De Grace.  The bird was seen daily through Monday, February 15.  It has since
been inconsistent and reliably reported only a couple times.  Whether the bird
is still present or not is difficult to know.    

A word about the photos.  All of mine were taken around 9:00 a.m. February 12.
I used a Nikon N70 Camera, Sigma 400 mm f5.6 lens, and 200 ASA fujichrome film
that was pushed one stop.  The image quality is fairly good, but some color
was lost (pink legs are visible in many of the photos) and all appear
significantly more grainy than the originals.  I apologize for the darkness of
some of the photos, but the lighting conditions were very difficult.  To my
knowledge, Mark Hoffman is the only other person to have gotten good flight
photos, and those were taken at the same time as mine.  Jim Stasz and Bob
Abrams both captured the bird at great distance while it was sitting on a
rock, and Bob's photos do show a wing stretch, though the primaries are not
close to fully splayed.  Two of Jim's photos are displayed on the website as
well.  Brian Sullivan and I both took photos February 9, but conditions were
even more difficult and my photos showed nothing of use and I would be
surprised if his did.  If any one else has photos of this bird PLEASE PLEASE
let me know.  It was a very difficult bird to photograph (mostly hanging out
on rocks 1/4 mi away) and anything you have might add significantly to the
record on this one.

GLOSSARY 
apical spot: white spot at the very tip of each primary.  Distal to the black
tips on the outer primaries. 
mirror: white subapical spot, usually on p10 or p9.  Note that with this
individual the mirror on p10 (left wing especially) merges with the apical
spot.  Note that "mirror" is not to be confused with "apical spot". 
mirror patch: My own term.  When this bird was flying towards us it was easy
to pick out from all other birds by the large spots at the tips of the wing.
This was a combination of the large white tips (mirror + apical spot) on p10
and the large white mirror on p9.  In most cases I use this rather than
"mirrors", since at least p10 on the right wing had no division between the
apical spot and the mirror.
primary numbering: I use p10 as the outermost (most distal) and p1 as the
innermost (most proximal). 
"string of pearls": Reference to the effect created by the white tongue tips
on p9-p5, which appear as a string of white spots extending along the outer
trailing edge of the wing, proximal to the black primary tips
tongue tip: white crescent proximal to the dark tip of each primary and distal
to the gray surface of the feather.  Most easily seen from below as it is
often obscured by overlapping feathers from above.  Unlike on Jon Dunn's Large
Gulls video, I do not refer to tongue tips as "mirrors".

About the identification of this bird:

	Though this bird has been widely touted on the hotlines as "Slaty-backed
Gull", there are still some questions with this bird, most notably, "is the
primary pattern correct?".  To my knowledge, the original observers have not
yet referred to it as anything except at "probable Slaty-backed Gull", and
most who have studied it since have used the same degree of caution.  I think
"probable" was dropped more because it was awkward to use than because the ID
was 100% established.  Many of those who have seen the bird have said that it
looks very good, but has several characters that are a little "off".  Among
those I've heard mentioned are:

- the trailing edge of the wing is not broad enough (most photos including
Harrison 1987 photo #460 and Goetz et al. 1986 Figures #1-4 show more obvious
white trailing edges to the wing).  Similarly some commented that the tertial
crescent was not broad enough - I judged it to be similar to that of most
Herring Gulls present.  One reviewer (working with the photos on the website
now, only two of which are at rest) suggested that the white "skirt" (i.e. the
secondary tips as seen at rest) were not as obvious as one would expect for a
Slaty-backed Gull.  I did see the "skirt" regularly when the bird was at rest,
but would think that its presence is highly variable and depends too much on
posture of the bird.  I would think the width of the trailing edge of the
secondaries in flight is a better character than when they are seen at rest.

- the "string of pearls" effect is not as obvious as one would expect (again,
the photos listed above do show more obvious "strings of pearls". 

- the mantle is on the pale end for Slaty-backed (in the field it appeared
slightly lighter than _graellsii_ Lesser Black-backed Gulls).

- the legs were not as pink as one might expect (perhaps this is related to
breeding condition)
- there was less head streaking than expected (again, a product of breeding
condition?).  This bird had a concentrated area of thin, dark streaking just
above the eye and going across the top of the forehead.   It also had a patch
of large, squarish, blurry brown spots on the lower nape, which (though
restricted to a small area of the nape) matched, to my eye, those shown in
Harrison 1987 and Goetz et al. 1986 very well.  

- One person has commented that the bill does not show a pinkish base and that
this may be a source of concern.  At least one photo (e.g.Harrison 1987 #460,
May photo) shows a bright all yellow bill, and obviously this feature must be
related to breeding condition, which (judging by head streaking at least) this
bird was close to attaining. 

	It seems to me that all concerns can be explained away by individual
variation.  Back color is known to be variable in Slaty-backed Gull, leg color
is variable in almost all gulls, and head streaking should be lost and bill
color should grow bright as the bird nears breeding condition.  In reviewing
Jon Dunn's Large Gulls video I notice photos of several birds that have wing
patterns as subtle as on this individual (especially when he discusses the
extreme wing patterns in Slaty-backed Gull).  Also, I note that some of those
shown do not have particularly wide trailing edges to the wings (especially
the bird flying away, shown just after discussion of wingtip pattern).  I
would also note that the extensively gray webs of the outer primaries are
obvious in all the photos and amount to a very pale looking underwing, unlike
Herring, Lesser Black-backed, and Great Black-backed gulls, and reminiscent of
Thayer's Gull.
	What we need now are reviewers with extensive experience with the species.
Bob Lewis has commented that it looks very similar to a bird he photographed
at Hatteras (in 1994?) but that he has been reluctant to identify.  Comments
are anxiously awaited - please post them either to MDOsprey, ID-Frontiers, or
privately to me (miliff@aol.com).  If you choose the latter, please let me
know whether I can distribute your comments to others, or to the two lists
shown above.     

What the photos show and do not show: 
	The photos accurately show the jizz of the bird, width of the secondary bar,
and most details of the wing pattern.  Note though that the exact pattern of
p10 on both wings cannot be discerned.  The bird was seen preening on several
occasions and on February 9 in particular, p10 on the right wing was
misarranged and easily viewed for 15 minutes or more.  P10 on the right wing
had an entirely white tip.  It was cut diagonally across the feather so that
outer vane had more white than the inner vane.  P10 on the left wing was
similar, but had a small subterminal dark mark, broad at the edges of the
feather but narrowing towards the middle so that the effect was actually of
two dark marks that did not meet in the center of the feather.  Back color is
not shown well in any of the photos.  On my computer the pink leg color, which
is visible in a few of the original slides, can not be seen.  The head
streaking is not really visible in any of the photos, though it was clearly
visible in scope views that same day.
 	The at rest photos by Jim Stasz show the overall shape and proportions, the
size and proportions of the bill, the extent of the tertial and scapular
crescents and the "double bumped" appearance to the head which was commented
on by many observers.  For some reason the size of the white primary tips
appears reduced in these photos (from what I remember and what my notes show)
- at rest this was one of the most obvious features of this bird and helped us
all pick it out from the numerous Lesser Black-backed Gulls.  They were larger
than on any other gulls present.      
	My notes have not yet been coalesced into a complete written description.  If
anyone would be willing to post theirs it would add considerably to the
photos.

Literature cited:

	Dunn, Jon et al.  The Large Gulls of North America (video). 1997.

	Harrison, Peter.  1987.  A Field Guide to the Seabirds of the World.  Stephen
Greene Press, Lexington, MA

	Goetz et al.  1986.  Slaty-backed Gull winters on the Mississippi River.
American Birds 40(2):207-216.

PHOTO CAPTIONS

Photo #1
	In flight from below, banking.  By far the best photo, the bird is close,
backlit, and the wing pattern is easy to view.  Small "string of pearls"
visible.  Note also the restricted black visible from below, due to gray inner
webs overlapping to obscure the black outer webs.  Note though that p10 of the
right wing is obscured, probably being flared back behind p9.  We can easily
see that p5 has a narrow subterminal dark bar on a white tip; p6 has an
extensive dark tip with a white apical spot and a small white tongue tip; p7
has a somewhat more extensive black tip, white apical spot, and white tongue
tip; p8 has an extensive dark tip, white apical spot, and a small white tongue
tip; p9 has a large mirror and large apical spot, with only a restricted
subterminal black bar, the mirror is asymmetrical so that it is larger on the
inner vane than the outer; p10 is not visible on the right wing, but has a
large white apical spot (product of large mirror merging with a large white
apical spot) and a very small dark subterminal mark (see "What the photos show
and do not show" above).  On the left wing p10 appears top have an all white
tip, and indeed it does.  Note that p9 also appears to have an all white tip,
but that this is not actually the case.

Photo #2
	In flight from below, flying towards us.  Does not add much to Photo #1, but
the trailing edge is seen again and is narrower than in many examples of
Slaty-backed Gull.  Small "string of pearls" visible.  Note also the
restricted black visible from below, due to gray inner webs overlapping to
obscure the black outer webs.  

Photo #3
  	In flight from below. Flying towards us again, adds little to above photos.
Small "string of pearls" visible. 
 Note also the restricted black visible from below, due to gray inner webs
overlapping to obscure the black outer webs.  

Photo #4
	In flight from below.  The outer primaries on the right wing here are
misarranged so that p10, p9 and p8 merge almost imperceptibly into one
another.  P7, p6, and p5 are still shown well on the right wing.  The left
wing is fartehr from us and harder to view, but shows the large "mirror patch"
on p9 and p10.  Small "string of pearls" visible.  Note the restricted black
visible from below, due to gray inner webs overlapping to obscure the black
outer webs.  

Photo #5
	In flight from above.  Uppersurface of left wing visible and shows mirrors on
outer two primaries merging to form one large "mirror patch".  Small "string
of pearls" visible.  Note the restricted black visible from below, due to gray
inner webs overlapping to obscure the black outer webs.  

Photo #6
	In flight from below.  Small "string of pearls" visible.  Note the restricted
black visible from below, due to gray inner webs overlapping to obscure the
black outer webs.  

Photo #7
	In flight from below.  Left wingtip flared, right wing gives good view from
below.  Small "string of pearls" visible.  Note the restricted black visible
from below, due to gray inner webs overlapping to obscure the black outer
webs.  

Photo #8 
	In flight from below.  Dropping in on some food at the base of the dam.  Only
the right wing is visible, but the primary pattern is easily visible.  Though
p10 is easily viewed here, the resolution is poor enough that the dark
subterminal mark is indistinguishable from the large white tip.  Small "string
of pearls" visible.  Note the restricted black visible from below, due to gray
inner webs overlapping to obscure the black outer webs.  

Photo #9 
	In flight from above, flying away.  Note that the trailing edge to the wing
is not particularly broad.  Wingtip pattern is very hard to discern in this
shot.   

Photo #10
	In flight from below.  P5 and p6 can be seen well on the right wing, p9 and
p10 form large "mirror patches" on both wings.  Small "string of pearls"
visible.  Note the restricted black visible from below, due to gray inner webs
overlapping to obscure the black outer webs.  

Photo #11
	Flying towards us.  Does not add much to the above.

Photo #12
	Sitting on rock. 

Photo #13
	Standing on rock.  Apical spots seem smaller than they did in field and
primary extension seems a bit longer.  Leg color barely discernable -
definitely not bright yellow though.