Shearwater Identification - Is this an Audubon's or Greater Shearwater?


Figure 1. This Shearwater was photographed during the Memorial Weekend (end of May) 1994, near 'The Point', a nutrient rich area on the edge of the Gulf Stream off Manteo, North Carolina. Photo copyright of Angus Wilson©, 1994

Introduction

In an effort to promote discussion on the Pelagics e-group, Paul Guris questioned the identification of the above shearwater, which I had used as the opening illustration in my web page on Gulf Stream pelagics. I chose the picture simply for its dramatic feeling of movement and the question of the bird's identification had not crossed my mind. It turns out to be a very interesting, and hopefully useful, exercise. A number of birders with strong pelagic credentials have since chimed in with their thoughts and I have taken the liberty of compiling these opinions on this web page, together with a zoomed-up image of the bird in question. Posts are added in the order they arrive and so hopefully, you should see the arguments evolve and mature as you progress down the page. I am also aware of additional off-line discussion of this bird which I have not seen. Thanks to Paul for getting the ball rolling and I look forward to more input from others.

About two weeks ago I solicited opinions on ID of assorted pelagic photos on the Internet. I'll start with the shearwater photo that can be seen at:

http://www.best.com/~petrel/NCarolina.html

I believe that the shearwater at the top of the page is a Greater, not an Audubon's. I'm basing this on the big build, very long wings, long bill, clean cap going up at the nape, extensive white between cap and wing, darker cap than shoulder area, and evidence of a dark bar running across the underwing.

Paul A. Guris, Pennsylvania (pguris@moneynet.com)


The "Audubon's" is a Greater. The jizz, in one second, said Greater. I think the key is the black of the cap is quite distinct, and pale feathering wraps up behind the neck. On Audubon's, the dark of the top of the head continues in a horizontal line to the wings, so there is no pale nape area. On Manx, behind the dark cap, there is white that goes up in a point toward the nape, but Manx has a dark area on the side of chest near the wing base -- thus, dark, pale, and dark again, as one goes from the bill to the base of the wing.

You can't see the black smudge on the belly because of shading. The vent area looks dark, so Manx would be ruled out by that. But, its the sharp black cap ending in a rounded bottom around the eye, and then pale to the wing base, wrapping around the nape, that it is clincher.

In reality, in one second I looked at the photo and said "Greater". I had to think about about "Why"!

Harry LeGrand, Raleigh, North Carolina (Harry.LeGrand@NCMAIL.NET)


This looks like a Greater to me.
Anon


Still looks like a greater to me in part because of the same plumage features you mention. The apparent very white belly doesn;t really bother me in terms of it being a greater. My impression, several months removed from seeing hundreds of these birds over the course of the summer off Hatteras, is that this field mark was variable within the species and in its evidence to the observer (meaning lighting/angle/etc. can obscure it). Plumage aside, the structure and wing shape are spot on for what I think of in Greater. Audubon's while still having pointed wingtips always seem more bulbous in shape in the forewing area. They have relatively short, sort of paddle-like wings while Greaters have longer, more evenly tapered wings as this bird seems to.

Of the 3 photos of Audubon's at Brian Patteson's website (http://www.patteson.com/) I think the second one offers perhaps the best comparison in wing shape and illustrates the forewing shape I'm trying to describe. It also offers a nice view of Audubon's bill structure to compare with Angus Wlison's photo. It also however shows what seems to be a paler area extending up on to the nape slightly more than I feel is typical of Audubon's but if one examines the 1st and the 3rd Audubon's images one can see the more typical dark area coming down around the sides of the neck (this character clearly varies to some degree also).

George Armistead, Philadelphia, Pennsylvania, (gla@sas.upenn.edu)


I agree with the original identification of Audubon's. I don't agree that the structure is incorrect for Audubon's; a freeze-frame picture of a bird in mid-soar may make it appear longer-winged than watching a live bird intersperse wing-flaps and glides. It can also be difficult to judge true size of a lone bird photographed without any references in the same frame.

I think that what seems "wrong" with this picture at first glance is primarily the appearance of a dark cap & pale nape, suggestive of Greater. I believe that this is an artifact of the light - the bird is backlit, and the sunlight is creating a paler area behind the head. The pattern isn't right for Greater, though: in Greater the dark cap would be sharply offset by a clear, pale nape; here, the dark "cap" connects with a brownish smudge, which is *then* followed by the pale-looking area.

Other details I believe support Audubon's: The broader dark trailing edge to the underwing & more extensively dark primary tips; apparent lack of dark markings in the axillaries; lack of dark smudge on belly (I agree this can be difficult to see in the field, but is usually readily apparent in still photos, and I don't think can be explained away by shadowing).

The photos on Brian Patteson's site (of Greater & Audobon's) are instructive; the bottom-most Audubon's picture shows a couple of birds that, while much more worn, show the same general pattern as Angus's picture.

Andy Guthrie, Port Chester, New York (Andrew.Guthrie@ey.com)


While it does appear long-winged in the photo, Angus' bird looks to me to be an Audubon's. The underwing pattern, especially, with the broad blackish border surrounding a fairly thin white center does not fit what I see on Greater. I've also noticed that photos of Audubon's consistently show a feature which may not be visible in the field- that is on the underwing near the body, there is a 'tooth-like' dark triangle which comes forward from the trailing edge, and slightly further out on the wing there's a similar 'tooth' which extends back from the leading edge. On some birds the effect is reminiscent of two "jack-o-lantern" teeth. I don't know if this is a consistent and reliable field mark, but it is somewhat visible in Angus' bird, and on the Patterson page photo no. 3 on the two right hand birds, in the photo in the Master Birding Guide (Vol. 1 pg. 69), and in Harrison's Seabirds (1985) plate 31. In the Nat. Geo Guide, it is shown as a thin connecting line in the area of the axillaries. On photos of Greater, the most I see is a thin, diagonal dark line connecting the front and rear edges. Also, these same references show Greater to have little or no dark leading edge on the inner wing,in contrast to Audubon's wide leading edge. I must say, though, that while I have seen many Greater Shearwaters, I've seen less than 10 Audubon's in the field. From those with more experience- how valuable is the underwing pattern on these birds?

Mike Cooper, Ridge, Long Island, New York, (mcooper@suffolk.lib.ny.us)



Figure 2. Here is a zoom of the above picture. This was not available when the first sent of responses were posted. Does this add anything?


I'll start by saying that I am by no means an expert with either of these species, although I have seen both in life on various occasions in the past. This discussion does intrigue me due to the nature of the sorts of cues birders use to identify particular species.

To throw my own speculation into the hat, I would have to fall into the Audubon's-type Shearwater camp. I've got a few reasons for this including agreement with Andy Guthrie's comments about lighting and inconsistencies in the distribution of lights and darks between the cap and wing. I further agree with Andy that the pattern of black-striped axillary feathers should be evident in the photo if this were in fact a Greater Shearwater. These feathers instead appear to be white.

I have a trickier time with Jizz from photos, but to me the bird is consistent with an Audubon's-type Shearwater in shape and bulk. The long-winged effect is probably enhanced by the fact the body is foreshortened somewhat.

Thanks for an interesting diversion to my day.

Chris Benesh, Tucson, Arizona (cbenesh@rtd.com)


Wow, this Greater/Audubon's photo is very eye-opening when it comes to single seabird photos. These have caused an amazing amount of pain and suffering in the past, but this is one of the best examples of misleading appearances in a photo I've ever seen. I am obviously not an East Coast shearwater person, but that does not stop me from being intrigued. At first glance, it really does look like a Greater Shearwater. But I am convinced that it is not. I fully agree with Chris Benesh that the foreshortening of the body, causing the wings to look long, is what is causing the confusion here. If you block the two wings and just look at the body, it is totally an Audubon's. (I am ignoring the blown-up shot because it would probably be more misleading, although in fact that version totally destroys its resemblance to Greater.) And of course a number of plumage features, mostly already mentioned by others, point clearly to Audubon's. Anyway what I was going to mention was that I recall a very similar photo from the West Coast that caused confusion between Buller's and Manx, something that just doesn't happen in the field (in flight at least).

Bert McKee, presently in Hawaii (bertmckee@hotmail.com)


I forgot to mention that the very pale sides of the neck and nape, which seem to be a cause for some concern in the identification of the bird as Audubon's, is something that can be caused by wear. I sometimes see this affect in very worn Manx and Black-vented shearwaters. The tips of dark feathers in seabirds normally become very pale and frayed with wear, and the contrast with the feather base is often quite striking (this causes the scaled or barred appearance one sees in worn Black-footed and Short-tailed albatrosses). The feathers on a seabird's neck are larger and "softer" (not as densely packed) than those on the crown, so the pale fringes become more prominent.

I don't know anything about molt in Audubon's, but worn shearwaters of a particular species can be seen at almost any time of year, because of differences in molt timing in age classes and the fact that some (probably unhealthy birds) don't molt at all.

Bert McKee, HI (bertmckee@hotmail.com)


Here are my comments regarding the supposedly mystery shearwater in Angus Wilson's website. My earlier comments supporting Greater Shearwater somehow got listed as Anon in Angus Wilson's website discussion on the mystery shearwater [This has now been corrected - ACW].

Just now I again looked at the original photo, and the blow-up. I don't see what the mystery is. The bird is a Greater Shearwater. I've seen thousands of them, and thousands of Audubon's, off North Carolina. I live in NC, and know these two species exceedingly well. Audubon's does NOT have a jet black cap that bulges downward below the eye in a rounded pattern; nor does it show the pale nape that this bird shows. Audubon's has the blackish from the bill in a more straight line through or just below the eye. Audubon's also has a more paddle-shaped wing, that seems somewhat rounded in back.

Greater has the field marks shown by the bird in the photo. This includes the tapered wings shown in the photo. NOTE: I'm doing these comments from memory, not referring to Brian Patteson's photos, photos in Harrison's field guide, etc. I don't know if that is a plus or minus, but I've seen enough of the birds to conjure up an image quickly.

Harry LeGrand, Raleigh, North Carolina (Harry.LeGrand@NCMAIL.NET)


I just tuned into the debate on the identification of the shearwater off Cape Hatteras in May 1994. I have the benefit of close to zero experience with Audubon's Shearwater - a few poor views in choppy seas off Cape Hatteras in the early 1990s. However, in Newfoundland we see Greater Shearwaters by the ba-zillion every summer. No way is this a Greater Shearwater.

The dark cap is not shaped properly. The line of definition between them dark and white is blurred or diffuse. On Greater Shearwater it is invariably a distinct, smooth delineation sweeping in one neat motion through the 'face' and over the back of the head, leaving a distinct white slash intruding almost around the back of the neck. The bird in the photo has a dusky nape, lacks the distinctive clear cut white intrusion over the back of the neck. I get the impression of a relatively thin bill, small head and long shallow keeled chest giving the bird the small shearwater look; unlike the more serious, heavy-duty, big billed impression of the Greater Shearwater. The underwings are too dark for a Greater Shearwater. The dark trailing edge of wing is noticeably broader than a Greater Shearwater. The underside of the wing of a Greater Shearwater gives the impression of showing far more white than dark. The underwing of the bird in the photo looks dark, hollowed out by white. Greater Shearwaters have contrasting dark flecks on the axillaries and inner most under wing coverts. The NC bird is stark white here. Then there is the lower belly. With such an excellent view of underside of the body there can be no excuse for not seeing the characteristic dark lower belly of the Greater Shearwater. Greater Shearwaters show extensive dark feathering on the sides of the rump that frequently merge with the dark undertail coverts. The North Carolina bird has high amounts of white on the sides of the rump.

I am confident this is not a Greater Shearwater. It is one of the small black and white shearwaters. I'd bet on Audubon's over Manx because of the extensive amount of paleness around the head and neck, and because of the apparent dark undertail coverts.

Bruce Mactavish, St. John's, Newfoundland, Canada (bruce.mactavish1@nf.sympatico.ca)


Looks like an Audubon's to me.

Ned Brinkley Cape Charles, Virginia (Phoebetria@aol.com)


Regarding the identification of the shearwater, I think the bird is an Audubon's for the following reasons:

1. Bill too thin and 'weak' looking (Stouter in Greater).

2. The darkness of the earcoverts do not seem too wrap far enough around the sides of the neck and seem to merge with a greyish shawl (Greater would look more capped, without the greyish shawl).

3. The underparts and underwings (particularly the 'armpits' are too clean-looking - messier and more unevenly marked in most Greaters - often with a darker belly spot visible).

4.There is a sharp demarcation between the ventral region and the tail (less clear cut, more mottled in Greater) and between the light and dark of the underwing.

4. The amount of black on the undersides of the primaries appears too solid and extensive. (Greater showing more of an intrusion of white along the primary shafts).

Although there may be some photographic illusion going on, the overall appearance is of a slim,'clean-cut' bird, not the scruffy, head heavy appearance of a Greater.

Julian Hough, Connecticut (Jrhough1@aol.com)


Angus, When I first saw your shearwater, I must admit that my first reaction was that it was a Great Shearwater. However, on my office wall, I have a rather good photo of a Great Shearwater, in a very similar pose, which I took in Senegal in October - and there are some similarities and some differences:

The head, cap and bill look similar. The brown shoulder mark on the Carolina bird is adjacent to the cap, but on the Senegal GS it is adjacent to the wing. The dark borders to the underside of the wing are very much broader on the Carolina bird, however this could be an effect of the light and bad focus - it is possible that the pattern of dark markings on the underside of the wings are similar - but the detail may have got lost in an out of focus picture. The large dirty belly patch on the Senegal GS is very obvious - it's questionable if it is there at all on the Carolina bird. The under-tail coverts are dirty with a fuzzy (but in focus) boundary on the Senegal GS - they look black with a sharp boundary (out of focus) on the Carolina bird. The following 3 ratios are compared in the table below:

The ratio of the distance between wingtips to distance between carpals
The ratio of the length of the bird to the width of the wing (measured in the same direction as the body in the middle of the secondaries)
The ratio of wing-span to bird-length. [This is not a very good ratio as differences in the orientations of the 2 birds could bias the conclusion rather more than the first 2 ratios].

wing-span/carpal-span bird-length/wing-width wing-span/bird-length

Carolina bird: 2.45, 4, 2.44.

Senegal GS: 2.20, 3, 2.8.

The conclusion is that: The Carolina bird seems to have a longer "hand" (shorter "arm"), more slender wings and a longer body and the differences would be rather more than I would expect for these 2 birds to be the same species. Further - the shape of the rear edge of the wing is different at the wing base - the Senegal GS has longer tertials than the Carolina bird which seem to be the same length as the secondaries.
 
 

I have also seen a lot of Great Shearwaters, but I cannot honestly say how much their plumage varies, however, the structural differences really make me question whether the Carolina bird is a Great Shearwater and I have not seen enough Audubon's to comment, save to say that the structure of the bird may be more consistent with Audubon's than Great Shearwater - I suspect it has been photographed in a particularly extreme posture.

Dick Newell, UK (Dick.Newell@Smallworld.co.uk)


Paul,
DEFINITELY an Audubon's! The structure and plumage are both correct for Audubon's but wrong in many ways for Greater. For starters, the bill is short and slim compared to the head, the head is small compared to the body, and the body is slim compared to the wings. So, if you back up a bit and compare the size of the head and bill with the size of the wings, you see a bird with strikingly different proportions from a Greater. Also, the tail is too long for Greater. As for plumage, obviously the clean white belly is very unusual for a Greater. I have seen birds with very limited belly markings but never, to my knowledge, without belly markings. But perhaps more importantly, the birds I have seen with reduced belly markings have also had reduced dark in the vent. This bird seems to have a fully dark vent so I think that combo is out of range for a Greater. Another problem for Greater is the cap/collar pattern. Although some Greaters are paler than others, I don't see much variation in their cap pattern. They always seem to show a sharply-defined cap bordered by a partial white collar, behind which is a variable dark smudgy shoulder patch. The bird in the photo seems to have the cap bordered by a dark smudge and then something that looks whiter. I've never seen anything like that on a Greater.

I hope these comments help. Best wishes, Michael O'Brien, Cape May, NJ (obrienm@algorithms.com)


Paul,
I had a chance to look at the photo in question and I now know why I hate to ID birds from photos, especially pelagics and birds were jizz is so important. Photos can make birds look "funky" and I think that is evident in the photo in question. I believe it is an Audubon's Shearwater, but the photo seems misleading. The underside of the primary's are too dark for Greater and the bill seems too small. Greater's tend to seem front heavy and Audubon's seem big bellied as in this photo. The white on the underwing seems clean with a wide border of black as Audubon's should. The cap seems to be confusing because there appears to be a lighter gray area forming a collar. I think this is partly due to back-lighting and possibly due to molt (when is the photo from?) but in any case it would be a cleaner white on a Greater. The amount of dark cap and extent it extends down past the eye is within what I would expect to see for Audubon's albeit on the darker side of normal. All I really want to see is the bird flap it's wings once and the ID would be easy, but no matter how long I watch it, it never flaps it's wings.

Mike Fritz, Seaville, New Jersey (kngfshr@sprynet.com)


This photo looks like an Audubon's to me. I think the very clear belly and the under wing pattern is indicative of Audubon's. Without any comparisons its difficult, but judging as you can, the build of the bird seems to fit Audubon's. That's my vote. I would hate to bet my thumbs on it though!

Jack Dozier, Alligator Pt., Florida (jdozier@nettally.com)


I just looked at your shearwater picture and am firmly in the Audubon's camp. The posts by O'Brien and Mactavish (and some others) pretty well sum up what I would have said.

Will Russell, Tucson, Arizona (russell@rtd.com)



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