Cook's Petrels off Sonora ? - further post

[Matthew O'Brien]

Thanks to those who have replied regarding my sightings of what I believe
to be Cook's Petrels in the Gulf of California off the Sonora coast.

In addition to the one distant photo I posted of a flock, I did observe on
different occasions perhaps 15 flocks of the petrels flying by or feeding
in relatively close proximity to the boat.  Some of these flocks were
within 150 ft.  My lack of photos at these times gives me great distress.  
(I was sailing the boat, with my camera below deck generally.)

I did not state the behavior of the petrels well in my first posting.  
When feeding, the birds hovered close to the surface of the water,
fluttering down onto it to snatch some unseen (to me) food.  Sometimes
they would alight briefly, other times they kept airborne while dipping
into the surface with their beak.

In flight, the birds veered rather substantially in the breeze, and flew
within 2-8 ft. of the surface while searching for food.

All of this feeding and flight behavior, even when first seen at a
distance, convinced me that the birds were some species of petrel.  Seeing
them closely confirmed this, primarily to me by the shape and size of the
beak and head of the birds, in addition to their continued behavior.

I believe I can rule out any species of tern due to a very markedly
different feeding behavior.


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[Robert O'Brien-5]

My brother Matt doesn't have much experience with pelagic birding so I've
been helping him with these remarkable photos and did the tentative id as
Cook's.  I didn't know anythng about the Vent report until later.

One important point with the photo.  In the lower right there should be a
clickable enlarger button, but it won't appear until you put the mouse in
that area.  Once enlarged to full, original-pixel size, you can scroll
left and right with the scroll arrows.  You can't tell much in the reduced
photo.

Bob OBrien
Carver OR



On Thu, 29 Oct 2009, Matthew O'Brien wrote:

> Thanks to those who have replied regarding my sightings of what I believe
> to be Cook's Petrels in the Gulf of California off the Sonora coast.
>
> In addition to the one distant photo I posted of a flock, I did observe on
> different occasions perhaps 15 flocks of the petrels flying by or feeding
> in relatively close proximity to the boat.  Some of these flocks were
> within 150 ft.  My lack of photos at these times gives me great distress.
> (I was sailing the boat, with my camera below deck generally.)
>
> I did not state the behavior of the petrels well in my first posting.
> When feeding, the birds hovered close to the surface of the water,
> fluttering down onto it to snatch some unseen (to me) food.  Sometimes
> they would alight briefly, other times they kept airborne while dipping
> into the surface with their beak.
>
> In flight, the birds veered rather substantially in the breeze, and flew
> within 2-8 ft. of the surface while searching for food.
>
> All of this feeding and flight behavior, even when first seen at a
> distance, convinced me that the birds were some species of petrel.  Seeing
> them closely confirmed this, primarily to me by the shape and size of the
> beak and head of the birds, in addition to their continued behavior.
>
> I believe I can rule out any species of tern due to a very markedly
> different feeding behavior.
>
>
> Join or Leave BIRDWG01: http://listserv.arizona.edu/cgi-bin/wa?SUBED1=birdwg01
>
> Archives: http://listserv.arizona.edu/archives/birdwg01.html
>
>

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[Kenn Kaufman]

This is intriguing.  Matt's description of the birds' behavior (hovering,
fluttering down to the surface of the water) sounds utterly different from
the flight style of Cook's and other Pterodroma petrels -- more like the
flight of a storm-petrel (and of course these birds are obviously not
storm-petrels).  I can't imagine a Pterodroma flying that way, even in calm
winds close to shore.  The description of behavior, coupled with the
photograph, suggests the possibility of Bridled Tern.  Bridled in my
experience can look somewhat "unternlike" at sea; it flutters and dips to
the surface more than it plunge-dives; and birds in the first cycle can be
very pale gray above and white below and can have a head pattern suggesting
that of Cook's Petrel.  Bridled Tern isn't known to be regular along the
coast of Sonora but it can be common a little farther south in western
Mexico -- for example, I've seen surprising numbers off the coast of
Nayarit.  At any rate, this is a possibility to consider.

By the way, kudos to Matt O'Brien for pursuing this instead of just leaving
the birds as mysteries.

Kenn Kaufman
Oak Harbor, Ohio




----- Original Message -----
From: "Matthew O'Brien" <matthewobrien@...>
To: <BIRDWG01@...>
Sent: Thursday, October 29, 2009 10:25 AM
Subject: [BIRDWG01] Cook's Petrels off Sonora ? - further post


Thanks to those who have replied regarding my sightings of what I believe
to be Cook's Petrels in the Gulf of California off the Sonora coast.

In addition to the one distant photo I posted of a flock, I did observe on
different occasions perhaps 15 flocks of the petrels flying by or feeding
in relatively close proximity to the boat.  Some of these flocks were
within 150 ft.  My lack of photos at these times gives me great distress.
(I was sailing the boat, with my camera below deck generally.)

I did not state the behavior of the petrels well in my first posting.
When feeding, the birds hovered close to the surface of the water,
fluttering down onto it to snatch some unseen (to me) food.  Sometimes
they would alight briefly, other times they kept airborne while dipping
into the surface with their beak.

In flight, the birds veered rather substantially in the breeze, and flew
within 2-8 ft. of the surface while searching for food.

All of this feeding and flight behavior, even when first seen at a
distance, convinced me that the birds were some species of petrel.  Seeing
them closely confirmed this, primarily to me by the shape and size of the
beak and head of the birds, in addition to their continued behavior.

I believe I can rule out any species of tern due to a very markedly
different feeding behavior.


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[Steven Mlodinow]

Greetings All

So, having never seen a Pterodroma actually feed (just zip around), how do they fly when they feed?

Surely not in big, sweeping arcs?

This may well vary from species to species, so is there anyone out there who can comment on the flight style of Cook's Petrels when in a feeding flock?

Best Wishes

Steve Mlodinow

-----Original Message-----
From: Kenn Kaufman <kenn.kaufman@...>
To: BIRDWG01@...
Sent: Thu, Oct 29, 2009 9:41 am
Subject: Re: [BIRDWG01] Cook's Petrels off Sonora ?

This is intriguing. Matt's description of the birds' behavior (hovering, fluttering down to the surface of the water) sounds utterly different from the flight style of Cook's and other Pterodroma petrels -- more like the flight of a storm-petrel (and of course these birds are obviously not storm-petrels). I can't imagine a Pterodroma flying that way, even in calm winds close to shore. The description of behavior, coupled with the photograph, suggests the possibility of Bridled Tern. Bridled in my experience can look somewhat "unternlike" at sea; it flutters and dips to the surface more than it plunge-dives; and birds in the first cycle can be very pale gray above and white below and can have a head pattern suggesting that of Cook's Petrel. Bridled Tern isn't known to be regular along the coast of Sonora but it can be common a little farther south in western Mexico -- for example, I've seen surprising numbers off the coast of Nayarit. At any rate, this is a possibility to consider. 
 
By the way, kudos to Matt O'Brien for pursuing this instead of just leaving the birds as mysteries. 
 
Kenn Kaufman 
Oak Harbor, Ohio 
 
 
----- Original Message ----- From: "Matthew O'Brien" <matthewobrien@...> 
To: <BIRDWG01@...> 
Sent: Thursday, October 29, 2009 10:25 AM 
Subject: [BIRDWG01] Cook's Petrels off Sonora ? - further post 
 
Thanks to those who have replied regarding my sightings of what I believe 
to be Cook's Petrels in the Gulf of California off the Sonora coast. 
 
In addition to the one distant photo I posted of a flock, I did observe on 
different occasions perhaps 15 flocks of the petrels flying by or feeding 
in relatively close proximity to the boat. Some of these flocks were 
within 150 ft. My lack of photos at these times gives me great distress. 
(I was sailing the boat, with my camera below deck generally.) 
 
I did not state the behavior of the petrels well in my first posting. 
When feeding, the birds hovered close to the surface of the water, 
fluttering down onto it to snatch some unseen (to me) food. Sometimes 
they would alight briefly, other times they kept airborne while dipping 
into the surface with their beak. 
 
In flight, the birds veered rather substantially in the breeze, and flew 
within 2-8 ft. of the surface while searching for food. 
 
All of this feeding and flight behavior, even when first seen at a 
distance, convinced me that the birds were some species of petrel. Seeing 
them closely confirmed this, primarily to me by the shape and size of the 
beak and head of the birds, in addition to their continued behavior. 
 
I believe I can rule out any species of tern due to a very markedly 
different feeding behavior. 
 
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[Chris Corben]

Hi all

> This is intriguing.  Matt's description of the birds' behavior (hovering,
> fluttering down to the surface of the water) sounds utterly different from
> the flight style of Cook's and other Pterodroma petrels -- more like the

Actually, I think it's quite in character, at least for Cook's Petrel.
Although I've watched countless Pterodromas flying, and maybe quite a lot of
them feeding, my observations of Cook's Petrels feeding in the ocean off New
Zealand stands right out. They almost looked like a flock of terns, often
hovering over the water and dipping down into it. Matt's observations (and
what you can see from his photos) seems perfectly consistent with Cook's
Petrels, to me.

Perhaps more than any other birds, Pterodromas show a staggering flexibility
in the way they fly. The same bird can half fold its wings and fly like a
rocket, or it can spread them wide and hover or flap along like a gull. I
have watched a White-necked Petrel lazily flying over land during a storm in
Queensland, looking more like a gull then a bird I usually think of as more
like an albatross. I once saw a Herald Petrel flying over an island with a
flock of Sooty Terns, and at first thought it was just one of the terns.

I would not be at all surprised to find this feeding behaviour of Cook's
Petrels is also found in other species, even if it isn't seen very often. My
guess is it's mainly a result of their current food source. Sometimes you
encounter petrels exploiting a prodigious, if maybe short-term food
resource, and when they do so, they can employ tactics you don't usually
associate with them.

Cheers,

Chris Corben


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