Mystery Shearwater from Ascension Island - August 2002


Richard White (RSPB Ascension Island Conservation Officer) sent me this picture of a small 'black-and-white shearwater' that was found in a garden on Ascension Island last week. It had visited the site on at least three consecutive nights, suggesting it might be scouting out potential nesting sites. The question is, what species is this? Readers may want to refer to a similar discussion "Separation of boydi race of Little Shearwater from Audubon's Shearwater" on Ocean Wanderers. Ned Brinkley referred to the occurrence of similar blue-footed shearwater in Cape May, New Jersey. Also click these links for more information on Little Shearwater and Audubon's Shearwater, including listings of proposed taxa.


Photo copyright Richard White© 2002

Richard points out that no small shearwaters are known to breed on Ascension, although sub-fossil remains of Audubon's shearwater have been found and a bird identified as Audubon's was found in a burrow on an offshore stack in 1959. The bird has blue feet which seem to indicate a Little shearwater, as does the extent of the white on the undertail coverts. However, the dark feathering extends over the eye. The indent of white around the edge of the ear coverts is reminiscent of the larger Manx Shearwater. Measurements are at the upper range for boydi but are the undertail coverts too white for this species?

Measurements:
Head and bill 62.5 mm
Bill length 25 mm
Bill depth 8.5 mm
Bill width 12.2 mm
Tarsus 36.0 mm
Center toe 35.4 mm
Center claw 5.7 mm
Wing 191 mm
Tail 83 mm

Comments please!


Map borrowed from Barry Weaver's excellent Volcano web site - check it out!



Comments on the photo and description

We had an interesting shearwater wash up at Cape May Point during a hurricane in the fall of 1998.  The bird was at the small end for Audubon's, and had fairly striking bluish/purple legs, similar to those pictured in the photo.  The undertail coverts were white, with the exception of the longest ones nearest the tail which were black.  The face was slightly more white than on the bird pictured from Ascension.  We toiled over it for quite some time and left the identification to those at the Philadelphia Academy of Natural Sciences.  It turns out that it was an Audubon's of the race "loyermilleri", which can occasionally show leg coloration like this.  Forgive me if I misspelled the subspecies name, I don't have a reference with me here.  It is mentioned in Birds of the West Indies.  I believe Louis Bevier dug up the reference.  In any event, you can get more details on the bird, including photos and video stills from Shawneen Finnegan.  It might be interest .

Brian Sullivan, Institute for Wildlife Studies, San Diego, CA



A friend sent me your website details and the featured Little Shearwater from Ascension Island.

I think it is just that - a Little Shearwater.  Don't be fooled by the lack of clear white above the eye - not all Littles have this feature. Where it
is clearly seen - the identification is certain but where not then Little cannot be ruled out. Without seeing the whole bird - I am fairly certain
that is what it is.

I've handled Littles in the Madeira Islands and have handled Audubon's in the Caribbean. The Cape Verde Little Shearwater is now very much persecuted and numbers are declining annually. Contrast this with the islands of the Desertas, Selvages and Porto Santo group ( all Madeira) where enforcement of protection and "National Park" status has all but ended persecution and resulted in ever increasing numbers. It is not surprising they should therefore look for new predator-free breeding areas such that islands off Wales (UK) and now Ascension may be prospected, although lacking colony stimulation.

Photos copyright of Bernard Zonfrillo© 2002

Attached is a shot of 2 different Little Shearwaters from the Desertas - as you can see - no clear white over the eye. Many birds are like this and it may be a feature of age. The Ascension bird is a little darker than my examples. The other shot is of a bird from the Azores that shows a narrow white line over the eye. In fact I realise that I do not have a shot of a "text book" Little with a large white area around the eye! Those
individuals are in the minority! Plumage is always a bit variable in shearwaters- some Manx have a clear neck-crescent while others have nothing.

As regards separating the small Shearwaters - one very easy way to do it is to examine their feather-lice. There are clear differences between Little, Cape Verde (boydi) and Audubon's Mallophaga such that anyone finding a dead one (or alive for that matter) should go over it carefully and remove the lice with fine-point tweezers, placing them all in a small vial of alcohol. Never cross-contaminate them with other birds or other species. Then send them to me!  Seabird lice are often host-specific such that they can not only pinpoint the bird species but also where it originated because lice also frequently evolve diagnostic subspecies. Seabirders should bear this in mind.

Dr. Bernard Zonfrillo, Ornithology Unit, Division of Environmental & Evolutionary Biology
Glasgow University, Scotland



It sure looks like an Audubon's to me (though it seems a bit small)  I've handled dozens of them in the Caribbean.  I've seen probably 100 or so Litttles in the South Atlantic and never seen one with a dusky face like the pictured bird.  I can't remember which race boydi is, but I didn't think any Little could have a face pattern so dead on for Audubon's.

Dr. Richard Veit, College of Staten Island, New York


We did have the Blue-footed shearwater you mentioned from NJ here at the Academy.  I think it has been prepared but may not have been accessioned into the collection yet. At any rate I couldn't find it, but the collection manager Nate Rice is in Australia at the moment and he would know where it is. As I recall the thinking at the time was that it was of the loyemillerri subspecies of Audubons.  I think this was orginally suggested by Louis Bevier who was working at BNA [Birds of North America] at the time.

VIREO has 2 photos by Bob Pitman of an Audubon's on land, presumedly to nest from the Line Islands in the South Pacific which shows bluish legs, and 1 photo of an Audubons on land by Rick and Nora Bowers from Little Tobago Island which shows bluish tarsus and and 1 bluish "toe" with pink webbing.

Matt Sharp, The Academy of Natural Sciences, Philadelphia



This bird looks remarkably like those P. assimilis breeding on the Kermadec Islands (ssp. kermadecensis). The photos below were taken last month on Cheeseman Island in the Southern Kermadecs.

Photos copyright of Paul Scofield© 2002
The measurements are pretty similar as well (see HANZAB). The only real difference between the Ascension bird and the Kermadec birds is the tail length and this reflects an overall trend for longer tails in the more "Audubons" influenced Little Shearwaters. One could argue that what we have here are a Sub-Antarctic species the true little shearwater (as exemplified by elegans) and a true Audubon's (as exemplified by l. lherminieri) that have a lot of intermediate "hybrid" populations. I suspect that DNA work will make many of the more northern little shearwaters into blue footed Audubons.

Paul Scofield, Curator - Vertebrate Zoology, Canterbury Museum, Christchurch, New Zealand



I looked through my photos and found the Audubon's pictures I took in Jamaica a few years ago. The dark cheeks of Audubon's do look something like the Ascension bird but the legs are pink, no trace of blue, and the undertail coverts are "dusky". I think Audubon's has a proportionately longer tail - not obvious on the Ascension bird picture.

Photos copyright of Bernard Zonfrillo© 2002
All these "allied" small isolated shearwater populations are best regarded as distinct species until their feather-lice or DNA is properly examined.
Lumping them all as one is probably not a good idea. Where feather lice have shown distinct differences DNA has backed that up in every case. It
really is important to get some parasites from these odd stray birds, and/or a blood,feather or tissue sample. Finders should bear it in mind.

Dr. Bernard Zonfrillo, Ornithology Unit, Division of Environmental & Evolutionary Biology
Glasgow University, Scotland



I finally found the pictures of the deceased Cape May Audubon's Shearwater from early September 1999 (8th).



Photos copyright of Shawneen Finnegan© 2002

I did go up to the Academy of Science and compared this bird directly with other Audubon's in the collection and it was a match. We decided that it was loyemilleri subspecies from Trinidad/Tobago area. The legs were blue, but the webs of the feet were pinkish. This bird had an ulcer on one of its feet that made it look much redder and purple around the affected area (see dorsal view).

Shawneen Finnegan, Tucson, Arizona
 
[Notice the limited dark feathering on the undertail coverts of the Cape May specimen compared to Jamaica bird shown above. Is this an artifact of the way the feathers are arranged or a genuine difference? - AW]


Photos copyright Richard White© 2002, Paul Scofield© 2002, Bernard Zonfrillo© 2002 and Shawneen Finnegan© 2002.
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