domestic Swan Goose x Barnacle Goose hybrid, Sweden, 8th July 2006 - copyright Carl Gunnar Gustavsson
(photo ID: 0941)
Apparently the bird shown above was much larger than typical Greylag Goose x Barnacle Goose hybrids.
As with other domestic Swan Goose hybrids it is difficult, if not impossible, to rule out the possibility that the domestic goose parent actually has a mix of Swan Goose and Greylag Goose genes. However in these birds there is no clear indication of Greylag involvement.
domestic Swan Goose x Barnacle Goose hybrid, Waal en Burg, Texel (Netherlands), 3rd October 2010 - copyright Joern Lehmhus
(plate ID: 0552)
The black bill and the bright orange legs are thought to point to Swan Goose over Greylag, but again this is not to say that both species could not have been involved.
domestic Swan Goose x Barnacle Goose hybrid, Malmoe (Sweden), 30th July 2011 - copyright Carl Gunnar Gustavsson
(photo IDs: 0932-0933)
The above ringed bird was hatched in Holland in 2002 and observed annually in Sweden. Note the feathered knob and all-black bill indicating Swan Goose involvement. Dsuky undertail markings are typical of many Anser x Branta hybrids, despite this feature lacking in adults of either parent species.
domestic Swan Goose x Barnacle Goose hybrid (with Barnacle Goose), Skane (Sweden), 1st July 2008 - copyright Carl Gunnar Gustavsson
(photo IDs: 1066-1067)
This one is also a dutch-ringed bird (I assume all the photos from Sweden show the same individual?).
probable domestic Swan Goose x Barnacle Goose hybrid, Welney (Norfolk, UK), 28th March 2009 - copyright Dave Appleton
(photo IDs: 0101-0102)
Swan Goose Anser cygnoides
Greylag Goose Anser anser
Barnacle Goose Branta leucopsis