Swan Goose x (Bar-headed Goose x Snow Goose) trigen

 probable domestic Swan Goose x (Bar-headed Goose x Snow Goose hybrid) trigens, Schrevenpark, Kiel (Germany), 16th August 2011 - copyright Joern Lehmhus

(Photo ID: 0656)

These birds look a lot like domestic Swan Goose x Bar-headed Goose hybrids, but close inspection reveals some Snow Goose influence too.  The long-hanging pale-edged greater-coverts must surely be a sign of Snow Goose ancestry, but it is hard to imagine any hybrid involving just Snow Goose and one other species looking like these.

Well, Joern has a likely explanation.  There are several Bar-headed Goose x Snow Goose hybrids at this location and one of them has been associating with the flock of domestic Swan Geese rather than its own kind.  So it seems very probable indeed that these birds are the trigen offspring of a domestic Swan Goose and a Bar-headed Goose x Snow Goose hybrid.

(See also: Swan Goose x Bar-headed Goose, Bar-headed Goose x Snow Goose) 
 

probable domestic Swan Goose x (Bar-headed Goose x Snow Goose hybrid) trigens, Schrevenpark, Kiel (Germany), 16th August 2011 - copyright Joern Lehmhus

(Photo IDs: 0657-0666)

 

probable domestic Swan Goose x (Bar-headed Goose x Snow Goose hybrid) trigens, Schrevenpark, Kiel (Germany), 18th November 2012 - copyright Joern Lehmhus

(Photo IDs: 0553-0563)

Swan Goose Anser cygnoides
Bar-headed Goose Anser indicus 
Snow Goose Anser caerulescens or Chen caerulescens