Gisborne pelagic (Oct 21) addendum: Manx Shearwater

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Matthias
Posts: 63
Joined: Sun Dec 06, 2015 11:50 am

Re: Gisborne pelagic (Oct 21) addendum: Manx Shearwater

Postby Matthias » Sat Nov 11, 2017 9:25 pm

Hi Sav,

the bird approached the boat from from 5 o'clock and went out of sight only a few seconds later at about 2 o'clock. When I first spotted it without binoculars, it looked clearly different from Fluttering or Hutton's Shearwater (which we had also seen in small numbers earlier on the day). It had stronger wing beats and because of the bright underside and the contrast between upper and underparts my first thought was that it could maybe be a gadfly petrel (maybe because I was specifically on the lookout for these). When I took the photos, it was clear that it was a shearwater. Nevertheless, the quick glimpse on the camera screen afterwards left me puzzled because it showed a bird that looked superficially like a Fluttering Shearwater, but I had expected to see something different. Regrettably, none of us had Manx on their radars, so we left the ID as "Fluttering Shearwater". I did not look at the photos again until I returned home. As soon as saw the photos on the computer screen, I noticed that this bird looked different from Fluttering and Hutton's Shearwater.

Cheers,
Matthias
Ian Southey
Posts: 1100
Joined: Tue Sep 08, 2009 5:45 pm

Re: Gisborne pelagic (Oct 21) addendum: Manx Shearwater

Postby Ian Southey » Sun Nov 12, 2017 7:44 am

I don't know what this bird is but have a few general remarks.

Normal variation in common species - There are tens, if not hundreds of thousands of Fluttering Shearwaters in New Zealand every year so it is perhaps more likely that an unusual bird is an extreme part of the normal variation or some rare colour variant than such an extreme vagrant. The quickest check of variation is to look at the pictures in http://www.nzbirdsonline.org.nz/species ... shearwater You can quickly see that there is variation on how white or dusky they are underneath and there is a photo of a bird from Burgess Island with an underwing pattern that approaches the bird in these photographs.

Regarding moult - this bird does appear to be in early primary moult. The holes in the outer primaries indicate that it is either in need of a good preen or these are juvenile flight feathers (not as strong) that need replacing. Looking up HANZAB (from nzbirdsonline) I see that Fluttering Shearwaters have been recorded with post juvenile moult of primaries from November and this isn't very much earlier. These pictures may be of a northern hemisphere adult, or a local first year bird.

Regarding lighting - If you look at the shadow cast by the leading edge of the wing it seems that the sun was almost directly overhead and slightly in front of this bird with light just glancing off the face so any surface irregularities will shade large areas. Thinking of the contours of the face in general - the crown bulges over the eyes a bit, the eyes are set a little deeper back, and the cheeks begin to puff out a little. I think the dark spot behind the eye is only shadow and I wonder if the light area on the cheek may be due to stronger reflection of light hitting more directly and angling it back toward the observer. I'm not sure that it is distinct enough to mean a great deal but if people pay attention to how these Fluttering Shearwaters look in similar positions it may be possible to come back to this bird.

I did not see this bird but I have seen Fluttering Shearwaters in a variety of situations and they can be over the shelf edge. The way they fly depends on the wind and maybe what they are doing at the time.

But I still can't say for sure just what this bird is.

Ian
Graeme T
Posts: 26
Joined: Fri Sep 29, 2017 2:17 pm

Re: Gisborne pelagic (Oct 21) addendum: Manx Shearwater

Postby Graeme T » Mon Nov 13, 2017 8:05 pm

Hi Matthias and Russ
Thanks for posting this interesting bird. Shows how difficult it is to identify birds at sea even when you have good photos to admire. The bird in question is not a Little shearwater. They have much shorter wings. The identification of it being a Manx seems based mainly around the white axillaries and the moulting of the primaries. There are some problems for the moult theory. Petrels and shearwaters have 10 primaries and they moult sequentially from the inner primary P1 to outer primary P10. Often in groups of 2-3 feathers. But a key point is primary moult occurs evenly on both wings. This bird does not have matching wing moult. There is no evidence of moult on the right wing (all secondaries are present and so are the primaries). The left wing appears to have primary gaps that are not sequential. Either because its lost some feathers randomly or they are tucked in some how (less likely). So I don't consider this to be a bird moulting in the non-breeding season. Secondly the extent of white in the underwing is quite variable in fluttering shearwaters. I have seen photos of flocks of both Hutton's and fluttering shearwaters where some birds seem to have totally white underwings. It may be related to bright sunshine "bleaching" the feathers in the photos or they are genuinely white. Either way I don't think its overly reliable. Even in the hand its fairly variable. Manx shearwaters in October would be much browner than birds in fresh plumage as the dark feathers fade to brown with wear (happens in all Procellariiformes). Manx shearwaters have long bills like Hutton's and also long wings as they are migrants. This bird does seem to have quite long wings. I can't totally eliminate this bird being a Manx but I would not be surprised either if it was a fluttering shearwater based on variability in plumage in that species. Cheers Graeme
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RussCannings
Posts: 1216
Joined: Wed Sep 24, 2014 5:23 am

Re: Gisborne pelagic (Oct 21) addendum: Manx Shearwater

Postby RussCannings » Mon Nov 13, 2017 10:19 pm

Thanks so much for this great feedback-- some very valid points coming forward. Graeme--It's tough to say for sure but I'd have to disagree with your moult assessment. To me the inner primary moult appears to be symmetrical (See first photo) with those ragged outer primaries on the left wing a feature of heavy wear, not moult (i.e. This bird is not in the relatively fresh plumage of resident Fluttering).

I absolutely take the point that a 'weird Fluttering' would be much more likely than a vagrant. But it's the combination of all features that has me still leaning toward Manx (i.e. Facial pattern, underwing, moult). That said I won't lose any sleep if enough doubt is cast. Sav is absolutely right that some birds just can't be IDed to satisfaction.

Cheers all!

Russ

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