Subject: Nov 6 Pelagic trip report
Date: Sun, 7 Nov 2004 09:04:22
From: William B McKinney
I think that it's pretty safe to say that the weather conditions on November 6, 2004 were the most pleasant
that any of us has ever experienced on the open Gulf of Mexico. Thirty seven lucky birders were treated to light winds,
nearly pancake flat glassy seas, mild temperatures and low humidity, with blue oceanic waters throughout the trip,
beginning close to shore. Many of us were convinced that Father Tom had put us as number one on his prayer list.
If we had had a crystal ball we could have billed the trip as "sunrise to sunset on the open gulf- a search for jaegers,"
for we had 27 jaegers throughout the day from 7:15 am to 3:15 pm. Most were Pomarine (16), but we also had six Parasitic,
and one Long-tailed. Most satisfying was the fact that most individuals were seen very close to the boat and studied at length.
It was great seeing the various ages, morphs, and plumages of Pomarine Jaeger, their flight style and behavior,
etc, as well as direct comparison with Parasitic Jaeger. On one occasion we had amazing looks at eight Pomarine Jaegers
sitting on the water together, flying close around the boat. The speed and agility of the jaegers were very impressive.
Speaking of size comparison, we were all fooled when watching a jaeger in deepwater preying on a small passerine.
The jaeger appeared so much larger than the Eastern Phoebe, that is was thought to be a Parasitic. It turned out to be,
however, a Long-tailed Jaeger. By the way, this was the third straight trip with Long-tailed Jaeger, a Texas Review Species.
It seems like every trip we're learning something new about the status and distribution of birds in offshore Texas waters.
On the other end of the speed and agility spectrum, came our most exciting bird of the day. Just as we were putting out
some yummy fish and popcorn chum at one of the deepwater Sargassum weedlines, came a large "lumbering" bird towards the
bow of the boat. Within thirty seconds or so, the bird passed directly over the boat at close range. Those of us who were
on the October 1 pelagic couldn't believe our eyes. It was clearly a South Polar Skua, but very possibly a different
individual from 6 weeks ago. The bird climbed a little higher, made a slight turn and continued at of sight.
Being stopped and having just laid out the fish oil slick, we decided to wait rather than fire up the engines
and lay chase. The bird did not return. Excellent photos were taken by Chris Merkord and maybe others). This bird
showed diagnostic field marks for South Polar Skua, including, massive tubular body shape, uniform gray plumage of
underparts, broad secondaries, and extensive white at the base of the primaries. Upon acceptance by the TBRC,
this could be just the second record for Texas and of the entire Gulf of Mexico. Martin Reid, wryly stated,
"Your chase trip for the skua (six weeks in the making) was a success."
Other pelagic species seen included one Audubon's Shearwater, two Masked Boobies, two Bridled Terns and one possible
Northern Gannet (near the jetties coming home). We also had a few migrants, including a Yellow-rumped Warbler that
flew on and off our boat for much of the trip. Hey, our boat was a safe haven in jaeger country. Also seen were a
Western Meadowlark perched on a shrimp boat, a deepwater White-wing Dove circling our boat, a couple of other
Yellow-rumped Warblers. Also had a few Franklin's Gulls and Common Terns as well as may coastal terns.
We were also treated to sea creatures of the birds, including both Atlantic spotted and bottlenose dolphins
(pelagic and inshore populations of bottlenose), two sea turtles, and loads of fish (mostly bonita but also one tuna).
All had a great time. Thanks again to the RGV Birding Festival and the
Harlingen Chamber of Commerce for including this pelagic as a last hour
pre-festival activity. We hope to make the November pelagic a regular trip in the future.
Thanks to all for supporting Texas pelagics.
Separation of South Polar Skua from dark Pomarine Jaeger
December 11, 2004
By: David Sibley
I was intrigued by this problem in light of the discussion surrounding the recent
(6 November 2004) bird from southern Texas (see photos here and here; and sincere thanks to
Martin and Chris for making these photos available and thanks to all who have participated
in the discussion and our collective education). We wouldn't think of this as a challenging
identification problem, but this is not the first time a contentious jaeger/skua has been seen.
This bird was identified from a boat as South Polar Skua, but several people who saw the
photographs raised questions, and an extended online discussion on the Texas listserve has
failed to establish any consensus on the identification of the excellent photos. I found the
Texas photos genuinely confusing, and started some research just to help myself understand the challenge.
Too often the discussion of shape and proportions is simply a vague and subjective claim of
"broader wings" or "large head" which is very little help to an inexperienced observer, and sometimes misleading.
In this case I think the appearance of a larger head on the skua is mostly an illusion created by the broader
body (thicker neck) and shorter tail, so that an observer trying to identify a skua by its "large head"
should be concentrating instead on other things. In the illustration below I have compared Pomarine Jaegers
on the left and South Polar Skuas on the right in flight in three different views, based on multiple photographs.
Some of the differences noted are well-known, others are not.
Here are the differences in no particular order:
South Polar Skua has broader wings relative to the body of the bird and relative to the wing length.
Pomarine Jaeger wings are narrower, appearing longer, and are often angled.
Skuas have less pointed wings. This is accentuated by the breadth of the wings.
In contrast to the narrow wingtips of the jaeger that are drawn out into a fine point,
the skua's wingtip forms a broader triangle and a blunt tip. This can vary to some extent
based on the wing position (a skua in fast flight in high winds can fold the wingtips back
to a sharp point) but differences should be clear in a series of photographs or an extended observation.
Skuas have broader bodies that taper very little from the chest to the belly. Jaegers tend to
have the body deep-chested and clearly tapered to the rear.
Skuas have shorter and broader tails than jaegers. The tail of Pomarine Jaeger is relatively long and narrow.
Because of the broader wings and shorter tails of skuas, the length of the tail appears less than the
width of the wings, while on Pomarine Jaeger the length of the tail appears about equal to the wing width.
Also, the skua's wings appear to be attached farther back on the body, whereas the Jaeger has a more
"balanced" shape and the wings appear to be attached around the middle of the bird.
These differences in shape and proportions seem quite consistent across series of photographs, and
I suspect there is no overlap between Pomarine Jaeger and South Polar Skua, although the differences
can be very hard to interpret from a moving boat and/or from a few photographs.
I intentionally left plumage details out of the illustrations, as I did not study them, and the
illustrations here should be interpreted only as silhouettes.
As for the Texas bird that started this research, plumage is an important part of the discussion.
As Martin Reid has argued that bird's plumage with apparently unbarred gray-brown body and head
contrasting with solid dark underwing coverts is wrong for any morph or age of Pomarine Jaeger
but perfect for South Polar Skua. So the Texas bird seems to have the shape of a jaeger and the
plumage of a skua, and which feature is more reliable and carries more weight in the identification
is still an open question.
Helpful collections of photographs are at Brian Patteson's Website and at Dick's Birds.
Also in books, especially Olsen and Larsson, 1997, Skuas and Jaegers.