Taiga (Middendorff's) Bean & Tundra Bean Geese, Lake Biwa

I visited the north of Lake Biwa last weekend (Nov 23), the first trip up there this winter. Woodland birding at dawn was good with species like Nuthatch, Willow Tit and Elegant Bunting that I don't usually see around Kyoto all quite common and easily seen.

There was no sign of winter passerines flocks yet, there wasn't any sign of winter for that matter. It was very mild shirt-sleave weather on the mountain top. Next it was down to Kohoku-cho to check whether the Steller's Sea Eagle had arrived yet, still a little earlier than its average arrival date but it was here on the 23rd last year. No luck I'm afraid. Nothing lives forever of course and there's always the worry that this could be the year it doesn't come back, it'll be a big miss when that day does come and we lose such a fantastic bird from our list of regular winter visitors.

Drawing a blank on the Eagle I switched my attention from the hill behind the Kohoku Wild-bird Center to the lake shore in front for a quick scan through the ducks and geese. As things turned out the quick scan that I didn't think I needed my hat for stretched into a much longer stint than planned. By the time I left not only wasn't there enough daylight to visit any good areas further south but I as I was to discover when I jumped in the shower that evening I had a semi-sunburn. That's semi as in the south facing side of my head, rather than semi as in a barely noticable tingle.

There weren't any rare geese present, a Swan Goose put in a surprise appearance last winter and there was a Greylag the winter before, nor were there even any of the Greater White-fronts which have become a regular feature in increasing numbers. However the interesting variation within the usual flock of wintering Bean Geese was enough to keep me occupied.

I've already posted a little on the differing size of some of the Beans at the lake and their bill/head shape range Here. Most of the geese at Kohoku-cho are middendorffii Taiga (Middendorff's) Bean but there also seems to be a small number of Tundra Bean Geese, presumably serrirostris, mixing in with them.

The taxonomy of Bean Geese still leaves questions unanswered and a few images of birds of unknown origin aren't going to confirm racial identity but at least the following digiscoped shots show variation occurring here. It's worth stressing I'm focusing on distinctive individuals in the images I'm posting today, there are (presumed) Middendorff's that might be far more difficult to put a name to if seen out of normal range.

"Middendorff's" Bean Goose is a very large and heavily built bird, the bill is deep-based narrowing towards the yellow band with what almost seems a parallel-edged extension. This is the typical appearance I think of as middendorffii at Kohoku but there seems to be a lot of bill variation within the taxon.  

Another typical long-billed bird. This was one of only two birds I noticed with white at the base of the bill. 

Deep-based triangular bills lacking the elongated tip extension like the bird in the centre aren't uncommon and this was one of three such birds at the end of the flock. At some angles they can seem quite droop-tipped with the combination of arched grin line, straight culmen and bulging lower mandible with a distal kink giving a forward pointing tip. These bills are strikingly different to those of the earlier birds though they seem to be otherwise indistinguishable. Such large geese must be Taiga and presumably this is variation within middendorffii. The bird on the left shows far more yellow than the norm and shows middendorffii can have more than the usual narrow band of colour. 

Another of the group of three deep-based, stubby-billed geese. The grin line is prominent and the lower mandible bulging.

To give an indication of just how large these Taiga Bean Geese are this is an old shot (8 Nov 2013) of a Swan Goose at Kohoku with the local Beans. Of course it could be a small female but nevertheless the comparison is useful.

So there's quite a bit of variation without suggesting anything beyond "Middendorff's" Bean Goose. However the following birds would be very difficult to shoehorn into middendorffii. My understanding of Tundra Bean from a European context is that it has a shorter, deep-based bill compared to the nominate Taiga Beans however this may be misleading from the Japan perspective as middendorffii has a very deep-based bill with a prominent grin patch and some bills are also clearly short and thus triangular, so it's possible that serrirostris might not be so obvious if you're relying on stubbier bills as an initial indicator.

Japan's Tundra Bean Geese winter further north than Kansai and I never get to see those populations. Finding the few birds that may be mixed in with my local Taiga is my only hope of seeing any. But what might they be? The OSJ list states serrirostris (Hishikui in Japanese) and curtis (Hime-hishikui in Japanese) occur in Japan. The former is the common wintering taxon and the latter is rare, though as it may or may not be a valid taxon and may or may not be identifiable in the field I'm not sure how its status can be assessed.

The Tundra I see here are significantly smaller and lighter in direct comparison. The juveniles present this day looked dorsally compressed with a flatter back line, more arched in middendorffii, and the belly less heavy or baggy behind the legs (Taiga is more like a Slaty-backed Gull to reverse the usual comparison). Thus these young geese actually look proportionally longer-bodied, which might not be expected of Tundra. The neck is slightly shorter but the difference is only really apparent when fully extended. They don't look any shorter-legged to my eyes.

With hulking Taiga towering over them on all sides this discrete group of small geese really caught the eye.

Taiga is deep-bodied with a high arching back and low rear belly, hence they look less long in the body, compare with the shot below.

These Tundra Bean Geese have a flatter back and straighter keel compared to the local Taigas. 

The sitting Tundra between the two middendorffii almost disappears into the minimal grass (it's not in a depression) whereas the deep-bodied birds sit high.

The necks are somewhat shorter and proportionately thicker though this isn't especially obvious unless you're looking for it but it may contribute to producing the clearly longer, sleeker-looking carriage of this group.

The small size of the birds in this group was obvious but even more eye catching was how brown they looked compared to Taiga. These juveniles are very distinctive with their plain brown breast and flanks and mostly unmarked scapulars, the narrow tips have mostly worn away, while a couple of more advanced individuals have replaced some rear flank feathers with adult type barring as well as a few darker scapulars showing fresh pale tips. The interesting question is where are the obvious  juvenile middendorfii? There were no stand-out brown juvenile Taiga Beans in the flock of about 200 nor do I remember ever having seen any here. This suggests they could moult into first winter before arrival which might be possible with a more southerly (earlier?) breeding population. It's certainly intrguing and it may be a very good way of picking up juvenile serrirostris in flocks of middendorffii in this area early in winter before their moult progresses to first winter.

Juvenile Tundra with uniformly brown neck, breast and flanks. Scapular fringes worn away and upperparts plain brown. This was the only one of this group that has a slightly convex culmen but as I'm yet to see even a hint of a bulge on the middendorffii this seems significant.

The bird in the centre has the deepest bill with most prominent grin patch of this group. The moult is slightly more advanced with a small number of next generation scapulars and rear flank feathers easily visible. 

The juvenile with the slightly convex culmen again.

Throughout the late morning and afternoon groups of 3-5 geese, perhaps family parties, would fly in to join the main flock and at one point the following single adult came in and landed with the group I was watching. I didn't pay it much attention at the time because the camera was attached to the scope but the incidental images (most out of focus) suggest it is also Tundra.

Though it's a little heavier than the juveniles the size and structure are a good match. The bill is short in relation to the head and there's even a slight forehead stop. The head is chunky with a less rounded hind crown and the neck is short compared to middendorffii.

Dropping in next to the juveniles. 

Short bill compared to head length and the deep-based there's a suggestion of a forehead stop unlike the long straight bill/forehead slope of middendorffii.  

 

Out of focus but still good to compare size with the sitting serrirostris juveniles to the right and middendorffii behind and to the left. 

With the middendorffii more alert this bird's small size is more apparent here. 

As it walked in front of the group of juveniles there's little doubt about the size and structure being similar.