Monday, 17 December 2018

Odd moult timing for Eastern Marsh Harrier?

After birding in Mie the day before, I drove up to northern Lake Biwa and up one of the dead end roads into the forested hill to grab some sleep before dawn. Glum might be a fitting way to describe the morning; the hills were weighed down by low, immobile clouds that early light made very little effort to penetrate. Even the effervescent Bulbuls couldn't muster more than the occasional half hearted, dank-muffled shriek. I persevered in the growning silence, for a while. My mental image of the lake bathed in sunshine, however improbable I knew this to be, proved irresistable.

Once down on the lake the sky overhead was actually blue! I may not have seen the sun but sunlight did reach through the clouds. That was as far as the good news stretched. The backdrop was purples and blacks, sometimes the hills sometimes the sky, there seemed a fluid exchange of hues between the two. This wasn't at all what the forecasters had predicted (Well there's a surprise!) when I was in Mie.

I took advantage of this belated and probably false dawn to welcome back our wintering Steller's Sea Eagle, sitting in its customary spot overlooking the customary line of parked cars and tripods, then check the Taiga Beans on the lake for anything less usual. There wasn't even the usual (that's Gt White-fronts) let alone less usual - I live in hope that the third time a Greylag turns up I will see it. Never mind, the Beans are always spectacular enough without any distractions.

The first drops of rain sent me back to the car before I'd finished scanning for the Red-crested Pochard apparently in residence this winter. If it had been there at the time, it should have stood out like a sore thumb, or giant duck. As it didn't I can console myself that I still wouldn't have seen it had I decided to (be less of a wuss) wait out a potential downpour without protection for my camera and lens.

Two or three minutes further south under a compromise grey pall, no more siren blue interludes, no longer threatening purple and black, I spotted something which really was unexpected; the Harrier of the title. A kerfuffle of Black Kites seemed unsure about what, or even whether, they were mobbing but nevertheless vaguely occupied the same airspace as a juvenile Eastern Marsh Harrier which had no such doubts about chasing off said interloper. This other bird had a distinctly narrow wing tip and was much smaller than the juvenile, this without being sufficiently small to cause serious excitement it must be added. It quickly gained height above the confusion and made off. The juvenile dropped back into the reedbed and the Kites went back to aimlessly wafting around waiting for food to surrender.

Cropped view of the interesting pointy-winged harrier. This is how it actually looked, black against dark grey with a strikingly narrow wing tip. The views were very brief before it was driven off. So, a photographic identification and grit removed from my oyster. 

Heavy cropping (and lightening) reveals p9 is about half grown and p10 is just showing. I don't recall ever seeing an Eastern Marsh, of any age, not having a full set of primaries, hence they must moult remiges at a time of year I don't normally see them (ie summer/autumn).

Due to its small size compared to the juvenile I'm guessing it must be a male. Having discovered p9-10 are still growing it's even easier to to eliminate the miniscule, narrower-winged Montagu's, which has amazingly occurred in Japan in winter. Pallid has also occurred in winter but is just as easy to rule out. Though it might be a better structural match for Hen once fully winged, the underwing pattern visible in the lightened images puts and end to any such notion. Though I don't have experience of older immature female Pied, in gradual transition from juvenile to adult, the lower belly through to the undertail coverts looks too dark I think. It may sound strange to say considering total records but Pied is perhaps the least likely rare harrier to occur in Honshu in winter. And though Northern hasn't even qualified for this paragraph so far, it has to be a better winter bet too.

I confess I'm not one hundred percent sure I've never seen a Marsh Harrier with this moult but I certainly don't remember having seen one. I'd guess this stage of moult would be more likely in an older immature (clearly it isn't juvenile, which wouldn't have started moulting flight feathers yet) because I suspect an adult would have finished replacing its primaries much earlier than December?

In both these images bird's right wing gives us the clearest view of the leading edge of the primaries and it's possible to see alula, very short p10 and half grown p9 creating a stepped effect. Plumage-wise, there's nothing that suggests it isn't an Eastern Marsh Harrier but I wouldn't attempt to sex it if I hadn't seen it in direct comparison with a much bigger (presumed female) juvenile. 

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