Saturday 16 September 2017

Io-to (Volcano Is) Sept 2017 - tubenoses

As anyone who read my last post about birds on hahajima will have realised I've been on a ferry trip. In fact I've been on the annual Volcano Islands cruise which for some reason, I've no idea why, was moved from the usual month of July to September. Apparently it will revert to July again next year. The July cruise is slap-bang in the summer breeding period and the ocean is almost crowded with seabirds going about their business. September was always going to be more of a gamble, not knowing how many of the breeders would still be around and in what numbers... but it is also right in the middle of seabird rarity season. If the Pacific weather patterns had been onside and if we had a good dollop of luck, we could have seen almost anything, especially thinking of how unexpected the Swallow-tailed Gull in Seatle was a week earlier!

Sadly pre-departure weather patterns were uninspiring and the ocean throughout the week-long journey never mustered more than a slight swell. As for the dollop of luck...? Well, there were single White-necked and Kermadec Petrels which certainly need luck but as they're both already on my Japan list it wasn't quite the luck I was hoping for.

Other than those two Japanese rarities the biggest difference between now and July was the absence of Bannerman's Shearwater. Or more accurately the near absence of small shearwaters. I saw two birds of interest, one north of Ogasawara which was so distant it might be better just to ignore it altogether but a second just north of Minami Io was in direct comparison with Wedge-tailed Shearwater which left no doubt that it was one of the small shearwaters. It was too far to identify but Bannerman's is by far the most likely in these waters. Also there were no Matsudaira's Petrels on this trip whereas there had been a small number in the far south on the July trip.

So two rare petrels, White-necked and Kermadec and I still wonder was I lucky or unlucky with these. It's not just a matter of having seen them before because that's definitely a good thing in the case of the White-necked. I dived into the ship's shop as soon as it opened at 07:00 to get my morning coffee and noticed a pterodroma fly by close to the ship through the window. In the hour and a half since dawn I'd seen 14 Bonin Petrels so I assumed it was another till I went back on deck and was asked whether I'd seen the White-necked that had been flushed by the ship. Technically yes I had but the views weren't tickable. So was I lucky that I actually saw it (I have seen several in the past) or unlucky because it appeared during my coffee run? Defintely unlucky in so much as I'm still left without a photograph of the species, not even a shockingly bad one. When the Kermadec was called I didn't get onto it until it was already behind the ship. After getting a quick look I tried to raise my camera but a sudden rush of lenses poking over my shoulder prevented me and in the end I could do no more than point in the general direction and fire off a spray of shots hoping the bird would be in one of them. It was, just; one of them. So I do now at least have a shockingly bad image of Kermadec, one up on White-necked.

A shockingly bad but amazingly lucky image of Kermadec Petrel. I suppose I could also say it's lucky that the bird is a light form otherwise it wouldn't be identifiable from the views I had. Incidentally some people got fantastic shots of this bird. 

A slightly better shot , this of an easily identifiable Bonin Petrel.

Bulwer's Petrel was far more common and as always a great bird too see as it doesn't (normally) occur on the northern ferry routes that I'm more familiar with. Though common it was also in far lower numbers compared to the July trip.

Nothing else in these waters habitually lifts its head so far above the body line in flight. 

Streaked Shearwaters are incredibly numerous in Japanese coastal waters but the Izu Is group is about their southern limit on the Ogasawara Is ferry route, beyond this point they are replaced by Wedge-tailed Shearwater. From my limited experienced it seems Wedge-tailed is more likely to push a little further north at times, slightly broadening the narrow area of overlap, I don't see Streaked similarly pushing further south into Wedge-tailed territory.

It's in the narrow area of overlap where it becomes so obvious how different these two species look. When I first came to Japan and made my first trip to the Ogasawaras I was looking at Wedge-tailed from the small Hahajima ferry and wondering whether my identification was correct. Now I wonder how I could have had doubts. Incidentally dark form Wedge-tailed seems relatively(?) rare here, the overwhelming majority are pale forms.

Wedge-tailed Shearwater. Field guides mention the shape and angle of the wings as identification features, the wings can indeed look longer and slimmer than those of Streaked and they are often angled at the carpal but I think these are only useful when already familiar with the species. The flight is also somewhat different to the more languid flaps of Streaked but weather conditions play a big part in how these features are perceived. I don't find tail shape terribly helpful as this is very dependant on viewing angle.
The real giveaway is the underparts, overall much duskier than Streaked. Streaked shows continuous gleaming white from the inner wing to the body, totally different to Wedge-tailed's isolated central wing panel which suggests a brighter version of Sooty Shearwater. The brown of the face extends low towards the throat, the breast side is frequently duller and brown extends right along the upper flanks and inner wing coverts producing an obvious break between the white body and wing panel, very obvious even at long range. The vent and undertail coverts are also srikingly dark.
Streaked Shearwater with extensively white innerwing coverts, up to the leading edge, continuous with the flanks and vent. This bird is fairly dark-headed, white-headed birds are just as readily identifiable when only the upperparts are visible.
Wedge-tailed Sheawater

Wedge-tailed Shearwater; that dark vent is very distinctive even as a bird is flying away.

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