Manx Shearwater inquiries
- Rusty, Mitch and Calbirders
I feel that I was quite careful when observing and identifying the two recent
Manx Shearwaters off San Clemente Island. Mitch is right though when he says
we must watch out for Manx fever! The birds were at relatively close range
(about 200 meters) and well-studied through 20-60 power spotting scopes. We
were careful to determine the colors of the plumages of known identity
species in relation to the lighting conditions. I've watched thousands of
BVSH at La Jolla in morning light and as Mitch points out, they absolutely
can look black and white and quite contrasty. Generally though, this effect
of the light diminishes with close range views and I feel comfortable that
when compared to the plumages of the Sooty/Short-tailed type shearwaters that
were seen, as well as the Pink-footeds and various species of gull and jaeger
present, that the plumage of the Manx type birds was assessed correctly. The
black of adult Pomarine Jaegers' mantle was unmistakable, as well as the dark
brown of the SOSH/STSH, as were the various shades of gray in CAGU, WEGU, and
Looking at one feature to clinch the identification of small black and
white shearwaters is always troubling. Being very familiar with Manx,
Black-vented and Audubon's, any one identification feature on these species
can be quite variable among individuals. The amount of white that wraps
around the upper rump sides (excellent Violet-green Swallow
analogy--McCaskie) is a good field mark but is especially variable. I have
photos of Audubon's Shearwaters from the Gulf Stream that have both
ear-surround and no white rump sides, and then some that show clean black and
white faces with the typical broad white rump sides (available on request).
Some have white above the eye (i.e. Little Shearwater) and some have dusky
dingy face patterns (i.e. Balearic Shearwater). I have seen many
Black-vented Shearwaters showing equal variation in the rump sides field
mark. Manx, however, seems less variable here, as all birds I've seen have
shown no white extending onto the upper rump. That said, I'm sure someone
has seen one with it, and my experience with Manx is of a magnitude much less
then that of BVSH or AUSH.
I have yet to see a BVSH with pure white underwing coverts and
axillaries as shown by these two individuals. If there's one thing I've
learned in birding though it's that one should never say "never" when it
comes to bird plumages.
The ear-surround field mark is also quite variable among the small
black and white shearwaters. Face pattern in general seems at best a
tentative field mark for identification. Manx do typically show the ear
surround but I'm not sure BVSH and AUSH don't typically show it either! At
least some largish percentage do. I feel the overall face pattern is more
useful (i.e. the demarcation between black and white), though again, this is
variable at times. I can recall seeing three Manx Shearwaters is a day back
in 95 on Monterey Bay in August on a Shearwater Journeys trip. Two were
typical, but one was much more brown and worn, causing some confusion. I
still think the overall pattern of Manx plumage is there, and comes through
even when worn, it's just that the blacks can turn to dark (and sometimes
fairly pale) brown. I can recall seeing some in the Atlantic is August
molting and worn and still darkish, but no longer black.
Undertail coverts are another problem. I have studied skins as well
as many live birds to determine the usefulness of this feature. Is it
variable--yes. But not nearly as much as some other ID features. On
occasion, Audubon's Shearwaters will show generally white undertail coverts.
Upon closer inspection, the longest of the undertail coverts merely have
black tips, while the shorter feathers and bases of the longer feathers are
white. What happens is the dark tipped feather blend in the black tail and
produce a pattern far from the dipped in ink long rear-end shown by most
birds of that species. I have noticed several Black-venteds as well with
whitish undertails. None of them, however, seemed clearly white, rather a
muddled blend of some pale browns and white at close range. I have not seen
a Manx with dark undertail coverts.
In a recent conversation with Debi Shearwater she said, "My experience
with Black-vents is that they really stay on the shelf, within 5 miles of the
coast. But, they do occur over the main canyon in Monterey sometimes. Anytime
I see a black and white shearwater offshore, I go for Manx first. I think it
is most likely that you are seeing Manx."
Like I said in my posting, black and white shearwaters are rare out
here on SCI. Being 65 miles offshore we see thousands of PFSH and SOSH, as
well as a variety of other pelagic species. I have seen but a few black and
white shearwaters out here, one was typical Black-vented while the others
have been too far to be certain. Just about a week ago I saw a bird from
China Point that appeared to show some of the field marks of Manx but was too
far for positive identification. On the morning following the original
sighting, Jonathan Plissner had a small black and white shearwater from West
Cove Point (the location of the original two birds), and he felt it looked
best for Manx but the conditions were poor and the sighting brief. I have
watched Buller's Shearwaters do giant circles and remain off West Cove for
quite some time while feeding so it may be that these two birds are (or were)
staying in close proximity to the island.
I don't have any experience with Townsend's or Newell's shearwaters
but I do have them in the back of my mind as a possibility. I certainly
would need excellent views, as Rusty suggests, to separate any of those
species. I do think it's only a matter of time, as Mitch says, before
someone documents both species with photos somewhere off California. Gotta
love those pelagic possibilities.
Institute for Wildlife Studies
PO Box 357054
San Diego, CA
[Non-text portions of this message have been removed]
Those interested in these identification issues may be interested in a
bird now being debated on my web site.
All opinions are welcome. Enjoy!
Joseph Morlan, Pacifica, CA 94044: mailto:jmorlan@...
Birding classes start Feb.5 in SF: http://fog.ccsf.org/~jmorlan/
California Bird Records Committee: http://www.wfo-cbrc.org/cbrc/