Update October 31st, 2007:

Since my original postings to ID-Frontiers, WestPal birds and Seabird News, I’ve received a great deal of feedback on this bird. Some of the correspondence has been extremely instructive,  and all of it has been helpful in some way. I’m very grateful to all who’ve involved themselves in the discussion.

Quite a number of all dark petrels and shearwaters have been suggested. They include Great-winged Petrel, Gray-faced Petrel, Bulwer’s Petrel, Jouanin’s Petrel, Mascarene Petrel, Murphy’s Petrel, Herlad Petrel, Fiji Petrel, Parkinson’s Petrel, Westland Petrel, Christmas Island Shearwater, Wedge-tailed Shearwater, and Flesh-footed Shearwater. The broad variation of opinion, I think, is partly a reflection on the images which, to put it plainly, aren’t too sharp making any type of detail difficult to discern - that’s one of the downsides of digibin images. On the plus side, given the brevity of the observation, at least we have some images to review.

Another confusing element may be the way in which the size of this bird has been described, including a “similar sized bird to Black-vented Shearwater”, or between “Black-vented and Sooty Shearwater in size”.  Described accurately, this would have made for a rather large, dark petrel opening up the possibility to some of larger species mentioned above, indeed quite a number of respondents have suggested Great-winged Petrel Pterodroma macroptera and Grey-faced Petrel Pterodroma gouldi.

Having watched several online videos of Great-winged Petrel, I am sure that the flight manner and size of this species (Grey-faced is sometimes considered conspecific with Great-winged Petrel) does not match my observations of the Santa Barbara Channel bird. With a wing span of around 100 cm, this would have made a potential Great-winged Petrel appear huge compared directly with Black-vented Shearwater (wingspan around 80 cm). Image #8 from my sequence doesn’t show a petrel with those proportions.

Over the last month or so, especially given some of the feedback received, I’ve thought seriously about the possibility of a mistake being made over the size assessment of this bird. Incorrectly assessing the size of seabirds has been well described in some recent texts (Onley and Schofield 2007, Albatrosses, Petrels and Shearwaters of the World), (Flood and Thomas 2007, Identification of ‘black-and-white’ Storm-petrels, British Birds July 2007 Vol 100), (Garner and Mullarney 2004, The Chalice Petrel revisited, British Birds Jluy 2004, Vol 97) and (Sibley 2002, Sibley’s Birding Basics).

As one of the observers involved, I’ve had the huge advantage of ‘seeing’ the bird in the field and thus, haven’t had to rely entirely on the images for clues to the identification. As described, my field impression was of a bird close to the size of Black-vented Shearwater, and with both Sooty and Pink-footed Shearwaters present in the same flock, I’ve been comparing the petrel with the smallest species of shearwater present at the scene. As one leading California birder told me in an email, “Black-vented is not a large shearwater”. Looking at Images #1 and #8 in my sequence, it’s possible to at least draw some comparisons with Black-vented Shearwater in size. On reflection, I’m pretty certain that the images show a bird that is actually smaller that Black-vented Shearwater, especially in terms of body bulk and wingspan. Looking at Image #8 it could be argued that the two birds are of similar length, much of the petrel’s length is made up of the tail which tapers nicely to blunt point. The bird’s body is actually rather slim, certainly slimmer than that of the Black-vented Shearwater.

This relatively thick-billed bird always looked like a petrel. The flight manner was loose, lazy and flexible with a very ‘easy’ flapping action. It flew in alone from the north, 4-5 meters above the water and initially gave pretty good views at eye level (we were on the upper deck of the boat). It circled the resting shearwater flock just once and didn’t attempt to alight on the water and join them. It departed just as suddenly as it had appeared, tracking a Black-vented Shearwater briefly (Image #8), before banking away alone to the north-east on a stiff western wind. Again, this is just my opinion, but I now think it’s probable that the long-winged impression, combined with the bird’s flight manner resulted in an over-estimation of the bird’s true size. To complicate things from our perspective, it appears to have been a wandering individual and didn’t engage in any active foraging, creating limitations for useful field guide comparisons on behavior.

Concentrating on the dark-petrels and gleaning as much information from references and the internet that I could find, I’ve narrowed down the possibilities to just two species, both from the genus bulweria. The combination of features shown in the images, along my own recollections and sketches, most strongly suggest - Bulwer’s Petrel Bulweria bulwerii and Jouanin’s Petrel Bulweria fallax. Both share the sooty-brown to black-brown coloration combined with long wings and the bluntly pointed longish tail, and both can show, to some degree, a pale brown upper crescent or carpal bar. In terms of more subtle features, both can show pale pink or flesh colored legs, an all black bill, and some grayish marks around the chin and the base of the bill.

Field identification of this species pair appears to be based on size and structural differences combined with an understanding of range. The identification is probably easy for birders familiar with both species. I would also imagine, given the limited range of Jouanin’s Petrel, that very few birders have had an opportunity to study both alongside each other.

For the less experienced, struggling to identify a lone ‘out-of-range’ individual, the identification may more problematic. Having done an extensive web search for images of the darker petrels, I’ve found the appearance of Bulwer’s Petrel to be extremely variable, much more so than I expected, especially those images taken in the Pacific. These images come across as showing a rather larger, heavier-billed and even shorter-tailed bird than many field guide texts imply. Links to the poorly known Jouanin’s are much more difficult to find, but they certainly give the impression that Jounain’s is a hulking petrel with a very heavy bill, and in my view, a much heavier bill than we saw on the California bird.

It’s also difficult to ignore the ‘blazing’ appearance of the upperwing crescents shown in the first image in the sequence. These appear neat and uniform, extending out to the primary coverts (on the right wing) and perhaps not attributable to wear alone. This image, although distant, looks remarkably similar to a number of Bulwer’s Petrel images to be found on the web. I wonder if Jouanin’s could ever show such visible upperwing crescents? Most references would suggest not, and that Jouanin’s only shows notable upperwing crescents when worn.

The vast majority of emails that I received on this petrel concluded that the bird was most likely a Bulwer’s Petrel. I struggled with this, really believing that I’d seen a much larger bird than my references described for Bulwer’s. Bulwer’s Petrel was even suggested by one of our party at the scene! On reflection, I believe that I (we) fell foul of the known problems regarding accurately sizing birds at sea. I was also unprepared for the broad range of variation shown in Bulwer’s Petrel images taken in the Atlantic, Pacific and Indian Oceans of which there are many available on the web and are worth reviewing.

I remain open minded about this bird, but currently believe that the overwhelming evidence points to Bulwer’s Petrel Bulweria bulwerii. On range this is by far the most likely, breeding as close to California as Hawaii. Extralimital Jouanin’s have occurred twice in Hawaii, but that would have to be regarded as truly remarkable for a bird of the Arabian Sea and Northwest Indian Ocean.

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Original Post, September 22nd, 2007: An unidentified dark petrel was seen during the very first morning of a ‘Birdfinders’ tour of Southern/Central California. We were crossing the Santa Barbara Channel on the Island Packers trip to Santa Cruz Island. Approximately just over halfway across the channel, the boat (‘The Islander’) slowed down to watch some Blue Whales. This gave our group the first opportunity to look at some ‘tubes’ at rest on the ocean, with a small group of Black-vented, Sooty and Pink-footed Shearwaters off the stern. Seemingly within seconds, Steve Lister drew our attention to a large, all-dark petrel approaching the stern from the north. I was standing next to Steve and got onto the bird straight away. I was astonished by its appearance. It was clearly a relatively large, wholly dark brown petrel, with a heavy bill and lazy languid flight. I began taking images through my bins straight away as the bird circled the resting shearwaters just once before arcing and gliding away to the north-east. The observation probably lasted less than ninety seconds in total, but at least five members of our party saw the bird reasonably well.


We were completely stumped. Some of the group looked around for our (then) extremely limited references with just two leading field guides aboard. We thought the bird most likely an all-dark pterodroma petrel, probably a Murphy’s Petrel. That evening, I left a phone message with Debra Shearwater describing our sighting in the hope that she’d put out a message on the local listserve, which she graciously did.


With a full tour to lead I didn’t have a chance to review my images on screen until September 20th. I became increasingly uncomfortable with an identification of Murphy’s Petrel due to the lack of several key features portrayed in the images. Based on his own memories of the observation, Steve Lister, the finder, sent me an email expressing similar doubts about the Murphy’s identification. In addition, several very experienced California birders had already told me that the time of year was inappropriate for Murphy’s with most reports coming from the April/May period, not early fall.

The images show this intriguing bird from a variety of angles, all of which were taken between 09:50 and 09:52 hours.

We have a couple of ideas regarding the identity, but would be fascinated to receive opinion from experienced pelagic birders.


Thanks very much in advance for any help received.

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