Tundra Swan help, China (1 Viewer)

[xuky.summer]

I saw several small groups of Tundra Swan today, and I found that the color of their necks was different. The small group was gray and white, while the other group was yellow or brown. At first, I thought it was due to age difference, but after looking at the photos, I found it was not. Is this group of Tundra Swan with colored necks stained by water or are there regional variations? Shandong province.
Thank you!

 

[Steve Lister]

Staining. The same happens to Whooper Swans wintering in the UK, the thinking being it is due to iron in the water/mud where they feed.

 

[Joern Lehmhus]

Typical staining , said to be due to organic iron compounds or something , as Steve mentioned already.

I have seen this also in Mute swan nand Northern pintail and Eurasian teal , inthe lattertwo also the breast and belly were affected

 

[xuky.summer]

Thank you all

 

[Joern Lehmhus]

https://cdn.download.ams.birds.cornell.edu/api/v1/asset/95342721/1800

comb duck with similar staining