Monday 14 February 2022

Baer's Pochard x Common Pochard and Ferruginous Duck x Common Pochard hybrids on Lake Biwa

EDIT: A 'new' bird was present 16 Feb and I've tacked on the end of the post.

 Since January of last year (2021) I've enjoyed an unparalleled opportunity (within my experience) to observe hybrids of these two combinations. There were often three birds coming into the same 'loafing bay' last winter. This winter two seemingly different birds were present in the same area in early December and they were joined by two more during January. Additionally, there were three other birds only four kilometres to the south, a couple of one-day birds in early November and another Ferruginous-type briefly in December. That's a scary number of hybrids within a very limited area of a vast lake, albeit an area particularly favoured by aythya.

But are they Baer's x and Ferruginous x Common Pochard hybrids, have I got this right? Well, I can't be absolutely certain, however birds with green heads and grey vermiculated bodies aren't likely to be anything other than Baer's x Common, and these birds have provided an crucial reference point. Others seem a good fit for Ferruginous x Common Pochard, but there are also birds that that are less easy to place and, if seen singly, would be even more problematic.  

Four hybrids together 27 Jan, 2022. It'll be clear from this shot that light conditions are as important as distance when it comes to getting meaningful views of the birds, let alone images. I had the benefit of scoping these birds for some time and for the record, I consider the right hand bird a Ferruginous hybrid, next to it is a green-headed and therefore Baer's hybrid and the other two have reddish-brown heads. I'm cautious about categorizing this type but Baer's x Common Pochard is the choice I'd lean towards.

Currently, there are four birds frequenting the same bay when not actively foraging. A green-headed bird (Baer's x), two with reddish-brown heads which look otherwise almost identical to the Baer's x, three peas in a pod springs to mind. The Ferruginous isn't so different at a glance either, so as it isn't possible to judge whether a bird is reddish-brown- or green-headed at any distance in dull conditions,  the pattern of the vent has become the easiest way for me to tell them apart. Each differs from the others even with the tail down, provided you can watch them at different angles. This is convenient for me to know which individual I'm looking at, but of no help from an identification perspective. 

So here are some of the best images starting with the green-headed birds; four images each of last and this winter's birds.

Four images of the same individual from 2 Jan 2021. I don't think there can be doubt about the progenitors in this case. If the birds are close enough, this neutral light can be best to assess details.

Reddish cheeks can be seen at close range with the sun behind the observer, not the case with the previous bird.

The same bird in poor light showing upperwing. A Ferruginous hybrid is in the foreground.

Moving on to the presumed Ferruginous x Common Pochard hybrids. The first was a lone bird (28 December 2021); three images. Followed by the bird present since late January; seven images.

At first I thought this must be one of the two brown-headed Baer's-types that had moved a little down the lakeside. However, when later checking the images I realized that it was a different bird and regretted not having spent more time with it. The reasons I now think this is a Ferruginous hybrid are its more compact appearance, it gives the impression of being shorter-bodied and sitting higher in the water. I'm tempted to simply say smaller size, which may well be the case, though that can't really be judged from the images. More significantly, the brown spilling from the breast onto the fore-flanks with very little change in colour (more obvious in the following image) seems indicative of Ferruginous as Baer's (and its hybrids) shows a sharp contrast at the breast side.

The eye is the darkest of any of the hybrids I've seen, though the brightness and colour tint of all the birds does change depending on angle and ambient light. It's worth noting that none of the hybrids have a truly white eye. The ventral markings showed this was a different bird to the presumed Ferruginous x that I first saw a month later.
The first view of the 'new' Ferruginous; 27 Jan 2022. The instant impression I got was of a much browner bird than the others I'd been used to seeing. Again the rather short-bodied and high-in-the-water appearance was apparent.

Closer views in better light; 2 Feb 2022. The overall brownness, yet again, depends on angle and lighting, it often doesn't appear as dark and brown as in this image and can look both lighter and greyer, particularly the flanks. Nevertheless, this image gives a more realistic overall appreciation when compared to the Baer's x Common Pochard hybrids and the similar reddish-brown-headed birds I'm tentatively calling Baer's x Common Pochard hybrids. In the field it almost looks a patchwork of even browns, this a result of the vermiculations of flanks and upperparts being less apparent and giving a less textured appearance. So, more uniform, slightly darker and browner flanks and noticeably darker and browner upperparts compared to the other hybrids present. The lighter and greyer impression it can give is always temporary. 

Here the Ferruginous (on the right) looks much closer in appearance to the reddish-brown (-headed) Baer's-type, though the flanks remain more uniform and the upperparts slightly browner. As the birds turn in the water the general similarity will pass and the Ferruginous regain its actual darker and browner appearance. Knowing these birds, I get a sense of the Ferruginous sitting higher and being shorter-bodied but realize to anyone viewing the image this can be dismissed as due to the angle and the possibility of unequal foreshortening, if recognized at all.  

And now to the more problematic birds, as mentioned in the first paragraph, which I'm tentatively calling Baer's x Common hybrids but are probably better left unidentified. These birds have reddish-brown heads which do not change as the winter progresses. My presumption that they are Baer's x Common Pochard hybrids is founded on them being essentially identical in size, structure and general plumage to the green-headed birds. The head colour is the sole qualitative difference. I do wonder about the shape of the head, it can look very pointed and often seems more suggestive of Ferruginous, but so, very often, does the shape of the green-headed birds. Though, as might be expected, these trickier birds can all show a browner or greyer cast to the upperparts, depending on angle and light. The only other diagnosable feature is the pattern of the ventral markings, and this seems to be random individual variation rather than moult related as there has been no change in appearance to any individual throughout winter. Four of the eight similar hybrids I've seen during the period have been this type, so perhaps this is the most likely type to be encountered as a single bird during winter; this as far as first filial hybrids are concerned of course.

The first bird, 2 Jan 2021; three images.

The second bird, 12 Feb 2021; three images.

The third bird, 2 & 11 Feb 2022; two images each date.

The fourth bird, 4 Feb 2022; three images.

Some questions:-

Have I come to the right conclusions as to the hybrid combinations?

Can eye colour be used to sex F1 hybrids? There are no strikingly white-eyed birds here.

If these birds are all males (?), then where are the females? Would a male Baer's x female Common produce a very different looking bird to male Common x female Baer's? In other words could these all be the offspring of male Common Pochard x female Baer's and offspring of the reverse gender pairing produce far more Baer's-like adults? The same can be asked of Ferruginous but if Baer's is declining in numbers and Ferruginous is not, it seems more likely that Baer's, whether male or female is more likely to be involved in hybrid cases even if Ferruginous x Common Pochard pairings aren't rare.

Are these birds all F1? Presumably so, they can't all be pale-eyed juveniles that are going to moult into something that could be mistaken for either of the putative progenitors.

Where are the F2 (and beyond), the back-crosses? This is where concern for potential misidentification of Baer's Pochard or Ferruginous Duck lies if the above birds are typical F1. There's no risk of misidentifying any of the above birds as anything other than a hybrid. But again, does the male of the progenitor pair have a significant influence on the appearance of the offspring?

I earlier mentioned a couple of additional birds I saw this winter which in the field I thought to be hybrids, looking at the images I began to have second thoughts but now the pendulum has swung back, and I have to accept that two potentially very interesting birds got away. If they were of mixed ancestry then missing out on the opportunity to get more details of their appearance is an even greater pity than missing out on Baer's and Ferruginous. Still, from a purely birding standpoint, finding both 'Baer's Pochard' and  a 'Ferruginous Duck' on the same day (only 18 minutes apart according to the photo data!) makes for a pretty good day; glass half full. Such a pity neither lingered, I wonder where they were headed?

The Baer's or Baer's hybrid, 4 Nov 2021; three images.

I may have been rash identifying this as a hybrid, though I think not. I did so because of the apparent paler markings on the upperparts, which could be nothing more than reflection (unlikely), as well as irregular, diffuse paler areas on the flanks, though plenty of ducks aren't in their prime the first week of November. It's just too distant to be confident about either way. If it is a hybrid, it's obviously not an F1 and therefore it's even more frustrating that this one got away.

Ferruginous Duck or Ferruginous hybrid, 4 Nov 2021; three images.

I'd put money on this being a hybrid. The images may not be as clear as I'd like but those consistent grey markings on the upperparts look perfect for grey stippling or vermiculations that are just beyond a comfortable distance to make out precisely. Another backcross viewing opportunity lost.

I'm always surprised how much time these hybrids spend in close proximity to each other; just coincidence? Are they more likely to select another hybrid as a mate? Even if they are this would only slightly limit dilution of the Critically Endangered Baer's Pochard's gene pool. Here are three images of a green-headed and reddish-brown-headed bird that that were never more than five metres apart, whether further out or closer in, during the two hours I spent there (11 Feb 2022).

Lastly, a possible Baer's x Ferruginous hybrid from five years ago (1 Dec 2016). When I first heard about this bird the message was the it was a male Baer's and there is certainly a close enough resemblance to render this a difficult bird to identify if seen way out on Lake Biwa rather than on a city park pond. 

Give this bird another 100m (or 300m...) and it would be looking pretty good for an early winter Baer's that hasn't acquired it's green head yet.

Fortunately it wasn't way out on a lake and at this range a few fresh feathers can be clearly seen on the crown... but they aren't the expected green. Bright reddish-brown fresh feathers contrast with the older, duller parts of the head which lack the reddish tints. This is beginning to look like a Baer's x Ferruginous hybrid.

But then there's the question of the extensive grey stippling on the upperparts. Could this indicate there was already Common Pochard influence in one (or both) of the progenitor pair? If nothing else, this bird shows the importance of adequate views with a suspected Baer's.

EDIT: Another bird turned up on 16 Feb. It stayed well out at the back of the flock but was suggestive of another Ferruginous x Common Pochard hybrid. I'm hoping for better views but no ducks were present on 18 Feb. That's no ducks, no Coots, absolutely nothing in this bay for the first time! In other loafing areas birds didn't start to arrive until 10am, much later than normal.

Three images of the new duck.

The new bird (back left) compared with one of the reddish-brown-headed tentative Baer's x (front right). The breast of this new bird is a distinctly paler brown than any of the other hybrids and the head a much clearer, brighter red. The eye may be duller and/or redder but closer views are needed to be sure.

No comments:

Post a Comment