Is this a Whistling Swan?

By Terry

China doesn’t yet have a rarities committee.  That will come as birding becomes more popular.  And so, for the time being, there is no formal way to assess reports of unusual birds.  I am therefore inviting readers of Birding Frontiers to informally assess a record of a putative WHISTLING SWAN (Cygnus columbianus columbianus) in central Beijing this winter.

This is the story.

For context, any wild swan in central Beijing (inside the 6th ring road) is notable.  So when local birder Shi Jin discovered a swan on 25 November on his local patch – the Wenyu He, between the 5th and 6th ring roads – he was very happy.  He was even happier when he noted that the bill showed a very small amount of yellow as it led him to believe that it just might be a Whistling Swan.   The significance of this sighting is that, if confirmed as a Whistling Swan, it would be the first time this North American form of Tundra Swan has been seen anywhere in China.

Although originally alone, the bird was soon joined by a standard Bewick’s Swan (the Eurasian race of Tundra Swan commonly encountered in China) and the two birds remained in the area for several days.  Shi Jin reported his sighting to Beijing birders on the day of discovery and circulated a photo, pointing out that it appeared to be of the North American race and asking for views.

The putative Whistling Swan in Beijing (with Bewick's Swan).  Photo by Shi Jin.

The putative Whistling Swan in Beijing (with Bewick’s Swan). Photo by Shi Jin.

On paper, separating the races of Tundra Swan – Whistling (columbianus) and Bewick’s (bewickii) – is relatively straightforward.  The most reliable feature is said to be the amount of yellow on the bill.  In his excellent Advanced Bird ID Handbook, Nils Van Duivendijk says that, in adults, “at most 1/8th of the bill is yellow in columbianus and that a large majority have less than 8% yellow on the bill.”  And that “the yellow is often positioned as a ‘teardrop’ on or just below the lores.”

Peter Pyle, in his Identification Guide to North American Birds, says that the yellow on the bill ranges from 0-16% and includes a helpful diagram showing the maximum extent (p.76 of Part II – Anatidae to Alcidae).

And David Sibley in The North American Bird Guide provides a similar diagram (p.73) of bill patterns, including an example of Whistling Swan “with maximum yellow”.

Of course, this is most relevant if the bird in question is an adult… (more about that in a minute).

As is evident, the extent of yellow on the bill of the Beijing bird is much less than one would expect on a standard Bewick’s.  The left-side of the bill even shows a classic ‘teardrop’ shape.    Initially the right side of the bill was not seen or photographed, although from a head-on view it seemed to exhibit only marginal differences.

In early December Beijing-based birder Jennifer Leung and I went to see the bird and we took a series of photographs (see below), including of the bill pattern and comparing the putative Whistling Swan with the accompanying Bewick’s.   These photos show that the bill is asymmetrical with a little more colour on the bird’s right side.  I use the word “colour” here as opposed to “yellow” as close examination of the images reveals that part of the coloured area on the right side of the bill is more pink-grey in colour and that the extent of yellow is limited and roughly the same on both sides of the bill.

Ageing

Now, back to that guidance about identifying adults.  As always, an important first step when attempting the identification of a potential vagrant is to age the bird.  On the Beijing swan, the general plumage – white body and wing feathers – appears to be adult.  However, there are a couple of aberrations that might suggest immaturity (I very much welcome views on these).  First, the crown has some dark feathering (viewable on several images over several days, suggesting that it is probably not staining).  Second, the area of colour on the right side of the bill is largely pink rather than yellow.  Is the latter evidence of an immature bird maturing and slowly developing its adult bill?  And, if so, is the amount of colour on the bill likely to reduce over time to leave the small patch of yellow, currently broadly similar in size and shape on both sides of the bill?

Once this question has been answered, the next obvious question is – “Does the amount of colour, and specifically the yellow, on the bill enable a secure identification?”

A cautionary note in British Birds (June 2006, BB 99, p307) on this issue stated:

“The two subspecies of Bewick’s Swan, C. c. columbianus and C. c. bewickii, have been proposed as potential splits because they differ in the amount of yellow on the bill (summarised in Sangster et al. 1997). However, it is not clear whether there is any overlap, and although hybridisation occurs there is virtually no information on the relationships between the two taxa in that part of eastern Siberia where they come in contact.”

And to muddy the waters further, it seems that Bewick’s from eastern Siberia (the most likely to turn up in Beijing) may have less yellow on the bill than standard Bewick’s.  Peter Pyle’s Identification Guide to North American Birds states “Populations [of bewickii] of eastern Siberia (“jankowskii”) may have bills averaging larger and with less amount of yellow but differences, if present, are insufficient and variable, and may indicate intergradation with columbianus.”

Aside from the yellow on the bill, other features have been suggested as helpful in separating columbianus from bewickii.

Cleaner white plumage

An article in Birding World (Vol 12, Number 3) reported that a Whistling Swan in Northern Ireland “stood out from its companions by virtue of being snowy white (A. McGeehan, pers. comm.)…”

Now, the Beijing putative Whistler did look, to me, marginally ‘cleaner’ white than the Bewick’s with which it was associating but how far this goes as a supporting feature is unclear.

Size and Structure

On average, Whistling Swans are slightly larger than Bewick’s but there is significant overlap so, for most birds not at the extreme end of the range, size will not be helpful.  Certainly with the Beijing bird, there is no significant size differential between it and the accompanying Bewick’s.

Some people have suggested that Whistling Swan exhibits a different head shape.  Birding World (Vol 12, Number 3) suggested that “While Bewick’s Swan tends to be rather dome-headed (with a smoothly rounded rear crown), Whistling Swan may show a different profile: a sloping crown ending in a high rear peak, and a steeply angled nape.”

To my eyes there is little, if any, difference in head shape between the Beijing birds.

Finally, the Birding World article referenced above asked the question directly:

“Can an out of range Whistling Swan be positively identified in the field?”

John Kemp, the author of the article, answered:

“Given adequate views, it seems likely that one of the 85% of classic Whistling Swans (ie those with less than 6% yellow) would be sufficiently distinct to be certainly identifiable, especially if it also showed good supportive structural features.  Photographs of reasonable quality may enable the percentage of yellow to be assessed.  The problem lies with the very small number of extreme individuals which cannot be convincingly identified, bearing in mind the existence of intergrades/hybrids….  ..Possibly only those individuals showing less than maybe 10% yellow on the bill should be regarded as true identifiable Whistling Swans.” 

For me, the right hand side of the Beijing bird shows more than 10% colour (with a smaller amount as yellow) but it is not straightforward to assess this accurately.  And, if it is more than 10%, does that rule out safe identification as a Whistling Swan?  Or should we only assess the amount of yellow?

Neither Shi Jin, Jennifer nor I have any experience with the North American form and we are far from experts on ageing swans, so we would welcome views from anyone with relevant experience.  But no pressure – it’s only a potential first for China!

Putative Whistling Swan, Beijing, 11 December.

Putative Whistling Swan, Beijing, 11 December.

2012-12-11 Whistling Swan right side

Putative Whistling Swan, Beijing, 11 December. Note the more extensive colour on the right side of the bill.

2012-12-11 Whistling Swan

Putative Whistling Swan (right) with Bewick’s Swan (left), Beijing, 11 December 2012. To my eyes, the putative ‘whistler’ looks slightly ‘cleaner white’ than the Bewick’s – a feature in support of Whistling as an id?

Note the dark markings on the crown - is this a sign of immaturity?

Note the dark markings on the crown – is this a sign of immaturity?  Photo by Shi Jin.

2012-12-11 Whistling Swan close up left side

A close-up of the left-hand side of the bill.

2012-12-11 Whistling Swan close up right side

A close-up of the right-hand side of the bill. Note the difference in extent and shape of the colour on the bill and also that the upper part of the coloured area is more pinky-grey. Is this a sign of immaturity?  Will that pink area turn black with age?

17 thoughts on “Is this a Whistling Swan?

  1. Paul Whiteman

    To me the ‘coloured’ areas of the putative Whistler look uneven and give the impression of some sort of abberancy rather than a genuine feature, there is something going on in the forehead region, with some greyish colouration too.

    Odd Bewick’s to my eyes

    Reply
  2. Harry Hussey

    I wouldn’t be in favour of acceptance of what seems to be an aberrant bird as a Whistling Swan: assuming that the pink areas on the bill of a young bird would turn yellow, as holds true for Whooper Swans anyway, there’s potentially far too much pale on at least the right hand side of the bill to allow for a safe identification. “Not proven” as Whistling Swan, for me.

    Reply
  3. Pim Wolf

    Hi Terry,

    apart from the dark crown patch this bird also appears to have some dark feathers on the rest of the head. If plumages of columbianus progress in a way similar as in bewickii those dark feathers are a sign of immaturity, you can often see this in 2nd winter bewickii as well. The bill pattern of those immature bewickii is already adult like. I think that the strange pattern on the bill of the Beijing bird cannot be explained by its age. Also the fact that the pattern is far from symmetrical points towards it being an aberrant.

    Reply
  4. Terry Townshend

    Hi Pim. Thank you very much for your comment. I think it is reasonable to expect bewickii and columbianus to progress in a similar way, as you suggest. With the views expressed so far, all from people I respect, we are moving towards the conclusion that the Beijing swan is an aberrant. However, for completion, I would love to hear from anyone in N America who has good experience of columbianus. Thanks again, Terry

    Reply
  5. Albert J. de Jong

    Hi Terry, the greyish feathers on the crown suggest 2nd winter in my opinion. In The Netherlands I use that character to score ages in flocks of Bewick’s since I hearded it from researchers doing work with Bewick’s. In Bewick’s, the bills of 2nd winter birds do only differ from adults by their paler yellow patch, not by pattern.

    Reply
  6. jhbirds

    Thanks Terry for a great post. As a waterfowl aficionado from North America, this bird peaked my interest. I’ve been looking closely at flocks of wintering swans in North America and have been lucky enough to encounter a handful of Bewick’s and presumed hybrids in Washington state.

    Ageing– I learned (from on this blog in fact) several years ago that second-year Bewick’s show some gray feathers on the head and neck. I have yet to see this on Whistling Swans in the field. It certainly seems likely they would have that as well. I can’t confidently say it doesn’t happen….it’s an answered question for me.

    On the China swan, between the gray on the forehead and pinkish tones in the bill, I would agree second-year bird is likely. I would expect these pink tones to turn yellow, rather than get darker by this age. The present amount of pink tones on the bill is more extensive than you see in most Whistling Swans. If I saw this in the western US, I would not pass it off as a Whistling. Its more likely I would start to get excited that its a potential Bewick’s or hybrid. The pale area is more extensive than you see on ~99% of Whistlings. I probably would not accept this bird as a Whistling if passed by me in a records committee setting.

    Thanks for the great post and comments!

    Jessie Barry
    Ithaca, NY

    Reply
    1. Terry Townshend

      Thank you, Jessie. It’s very helpful to receive an authoritative view from North America. It’s even more helpful as your view is consistent with the views expressed on here by European birders. Thank you again for taking the time to comment! Terry

      Reply
  7. Terry Townshend

    Thank you, Albert. It’s good to know that the bill on the Beijing bird is not likely to change in pattern with maturity but, instead, the pattern will likely become darker yellow. More evidence that the Beijing bird is likely an aberrant Bewickii.

    Reply
  8. Nial Moores

    Hi,

    Thanks for the post and discussion: interesting stuff!

    There seem to be multiple odd things about the bill and bare skin that rather suggest an aberrant individual or perhaps (less likely?) a hybrid. Of possible interest to the discussion (?) and / or to Chinese birders : one or more putative Bewick’s X Whistling Swan intergrades were seen or photographed here in the Republic of Korea in at least two or three recent winters between 2006-2010. Probably the clearest image we have on-site is from December 10th 2009 at:
    http://www.birdskorea.org/Birds/Birdnews/BK-BN-birdnews-2009-12.shtml
    This photographed individual at least had a smilar bill pattern on both the left and the right sides of the bill, with ID based primarily on the reduced area of yellow on the bill. One individual (from 2006) was thought to show even less yellow on the bill than this 2009 bird, and also to be structurally different from the group of Tundras it was with – yet still to have more yellow than the vast majority of pure Whistling Swans.

    Best wishes and birding,

    Nial Moores
    Birds Korea

    Reply
    1. Terry Townshend

      Thank you for your comment Nial..! Clearly there are intergrades out there in East Asia and, together with the odd aberrant bird, birders in this region must exercise caution before we can add this subspecies to our respective national avifauna… Thanks again for commenting – it’s always fascinating for us in China to hear about what’s happening over the water in RoK… Best wishes, Terry

      Reply
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