Cook's Petrels off Sonora ?

[Matthew O'Brien]

This photo shows a mixed flock of petrels and storm-petrels taken very
close to shore along the coast of the Gulf of California just north of
Guaymas, Sonora, Mexico.  (http://rdrop.com/users/green/petrel/petrels.jpg)

This photo was taken on Tuesday, September 29, 2009 around 4 PM.  The
photo is a relatively narrow horizontal slice cut from the original to
preserve the photo quality, but not create too large a file size. I
apologized for the distance to the birds - and their size.

Within this flock - and many others that I saw from 9/25 to 9/29 - are
petrels whose identity I believe to be COOK's PETRELS, or much less
likely, Stejneger's Petrels.  

The best example, I believe, is the bird that is fifth from the right,
wheeling away and showing its underparts.  Compare its size to the fourth
bird from the right, a much smaller Storm-petrel which I believe to be a
Wedge-rumped.  Others can be picked out across the photo.

During our five days at sea, I encountered mixed flocks of petrels perhaps
15 times.  Flocks were typically composed of 15-35 birds.  Some smaller
groups would be seen flying by, but all feeding flocks had a larger number
of birds.  These birds began occurring about two miles north of Bahia San
Carlos, and extended up into the channel between Isla San Pedro Nolasco
and the shore to its east.  We were never more than three miles from shore.

My primary conundrum with these sightings are that all sources say that
Cook's Petrel is a bird of the open ocean, deep seas.  These flocks of
petrels ranged out to our maximum distance from shore of three miles, but
also came into the mouth of coves in which we anchored.  The distances to
adjoining vertical cliffs was several hundred feet, and in some cases a
few birds came briefly into the coves to within several hundred yards of
the beach.  Water depth was about 10-15 fathoms maximum at these cove
entrances.

Not withstanding the reports this year of unusually high amounts of Cook's
Petrels in the Pacific as far north as Monterey - it seems an
extraordinary location: along the Sonora coast of the Gulf of California
in shallow water near shore?

There are two mitigating facts which I've considered:

Hurricane Jimena, a very large and powerful hurricane, sliced up the
Pacific side of Baja California and hooked onto the peninsula near Cabo
San Lazaro and entered the Gulf between Santa Rosalia and Mulege -
southwest of Guaymas.  Jimena then stalled just off Guaymas on September 3
& 4, and rainfall totals for 36 hours were around 40 inches of rain.  
Heavy flooding occurred. Could this storm have blown in these large amount
of petrels?

Second, the flooding on land created large amounts of nutrients in the run-
off.  We were able to observe massive amounts of fry, small minnows,
shrimp and other small food sources in schools all along shore.  This
sudden bonanza of available food attracted large mixed flocks of pelicans,
frigatebirds, cormorants, seagulls, terns, Brown Boobies, etc. to feed in
flocks in the light surf right along the beach.  The petrels didn't
venture this far, however.

I would appreciate the comments and advice of anyone familiar with west-
coast pelagic birds - a skill I've not developed that well.  Thanks.


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[Lethaby, Nick]

There are a few records of Cook's Petrels from the Salton Sea so they certainly occur in the Gulf of California. Given the large number of Cook's that were relatively close-in to CA this year (although still beyond the continental shelf), I don't think it's impossible you could have seen Cook's, although I agree that you should be questioning the circumstances. It's a pity the photos aren't closer. The birds might well be Cook's Petrels. However, I don't think one can even rule out terns of some kind - not suggesting that they are - but the photos basically aren't much use.


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[Brian Sullivan-5]

Matt

I agree with Nick that these possibly look like terns. The dark backs and white underparts suggest Black Terns, which would be expected at this time of year in that location. I've recently seen photos of large flocks of these in the inshore waters off west Mexico.

Thanks

Brian

On Wed, Oct 28, 2009 at 9:50 AM, Matthew O'Brien <matthewobrien@...> wrote:

This photo shows a mixed flock of petrels and storm-petrels taken very
close to shore along the coast of the Gulf of California just north of
Guaymas, Sonora, Mexico.  (http://rdrop.com/users/green/petrel/petrels.jpg)

This photo was taken on Tuesday, September 29, 2009 around 4 PM.  The
photo is a relatively narrow horizontal slice cut from the original to
preserve the photo quality, but not create too large a file size. I
apologized for the distance to the birds - and their size.

Within this flock - and many others that I saw from 9/25 to 9/29 - are
petrels whose identity I believe to be COOK's PETRELS, or much less
likely, Stejneger's Petrels.

The best example, I believe, is the bird that is fifth from the right,
wheeling away and showing its underparts.  Compare its size to the fourth
bird from the right, a much smaller Storm-petrel which I believe to be a
Wedge-rumped.  Others can be picked out across the photo.

During our five days at sea, I encountered mixed flocks of petrels perhaps
15 times.  Flocks were typically composed of 15-35 birds.  Some smaller
groups would be seen flying by, but all feeding flocks had a larger number
of birds.  These birds began occurring about two miles north of Bahia San
Carlos, and extended up into the channel between Isla San Pedro Nolasco
and the shore to its east.  We were never more than three miles from shore.

My primary conundrum with these sightings are that all sources say that
Cook's Petrel is a bird of the open ocean, deep seas.  These flocks of
petrels ranged out to our maximum distance from shore of three miles, but
also came into the mouth of coves in which we anchored.  The distances to
adjoining vertical cliffs was several hundred feet, and in some cases a
few birds came briefly into the coves to within several hundred yards of
the beach.  Water depth was about 10-15 fathoms maximum at these cove
entrances.

Not withstanding the reports this year of unusually high amounts of Cook's
Petrels in the Pacific as far north as Monterey - it seems an
extraordinary location: along the Sonora coast of the Gulf of California
in shallow water near shore?

There are two mitigating facts which I've considered:

Hurricane Jimena, a very large and powerful hurricane, sliced up the
Pacific side of Baja California and hooked onto the peninsula near Cabo
San Lazaro and entered the Gulf between Santa Rosalia and Mulege -
southwest of Guaymas.  Jimena then stalled just off Guaymas on September 3
& 4, and rainfall totals for 36 hours were around 40 inches of rain.
Heavy flooding occurred. Could this storm have blown in these large amount
of petrels?

Second, the flooding on land created large amounts of nutrients in the run-
off.  We were able to observe massive amounts of fry, small minnows,
shrimp and other small food sources in schools all along shore.  This
sudden bonanza of available food attracted large mixed flocks of pelicans,
frigatebirds, cormorants, seagulls, terns, Brown Boobies, etc. to feed in
flocks in the light surf right along the beach.  The petrels didn't
venture this far, however.

I would appreciate the comments and advice of anyone familiar with west-
coast pelagic birds - a skill I've not developed that well.  Thanks.


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--
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Brian L. Sullivan
Pacific Grove, CA

eBird/AKN Project Leader
www.ebird.org
www.avianknowledge.net

Photographic Editor,
Birds of North America Online
http://bna.birds.cornell.edu/BNA

Cornell Lab of Ornithology
159 Sapsucker Woods Rd.
Ithaca, NY 14850

Photographic Editor,
North American Birds
American Birding Association
www.americanbirding.org

bls42@...
609-694-3280
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[Kimball Garrett]

I can't disagree with those who long for a better photo, but I think the
photo does show small, pale Pterodroma (almost certainly Cook's by
locality and circumstance).  A few of the individuals show wings
distinctly angled at the wrist joint, and at least one on the left shows
a grayish hood that matches Cook's. The birds look pretty gleaming white
on the underwings for Black Terns.  

As for timing, the peak movement of Black Terns in the upper Gulf seems
to be from early August to mid-September (based on sixteen August to
October visits to El Golfo de Santa Clara at the head of the Gulf); peak
fall movement just to the north at the Salton Sea is in the first half
of August (Patten et al., Birds of the Salton Sea).  Certainly Black
Terns can be moving past Guaymas at the end of September (and Russell
and Monson cite Sonora records to the end of October), but it's late for
good numbers.  Having said that, I certainly can't rule out some of the
darker-appearing birds in the photos as Black Terns.

The timing for Cook's Petrels matches the general phenomenon of
warm-water seabird movement into the Gulf during monsoon conditions from
May to October.  I have seen a small Pterodroma, almost certainly
Cook's, once at El Golfo (22 May 2006, following a period of strong
southerly winds).  Jimena is certainly a reasonable culprit for pushing
petrels into the Gulf, and in general this has been a better than
average year for some warm-water birds (notably Blue-footed Booby) at
the Salton Sea and elsewhere in the southwest (though booby occurrence
is not likely to be directly storm-related).

If there is a storm-petrel in the photo, it is hiding behind a swell on
my monitor.

Kimball

Kimball L. Garrett
Ornithology Collections Manager
Natural History Museum of Los Angeles County
900 Exposition Blvd.
Los Angeles, CA 90007 USA
213-763-3368
kgarrett@...


-----Original Message-----
From: NBHC ID-FRONTIERS Frontiers of Field Identification
[mailto:BIRDWG01@...] On Behalf Of Matthew O'Brien
Sent: Wednesday, October 28, 2009 9:50 AM
To: BIRDWG01@...
Subject: [BIRDWG01] Cook's Petrels off Sonora ?

This photo shows a mixed flock of petrels and storm-petrels taken very
close to shore along the coast of the Gulf of California just north of
Guaymas, Sonora, Mexico.
(http://rdrop.com/users/green/petrel/petrels.jpg)


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