I know very well the bird you mean. I photographed it approximatly three months ago. I am also no expert on canada subspecies but it reminded me alot of the cackling geese that I have photographed at Slimbridge.
No need for a mad rush to the flash to catch up with this bird! I noticed it atleast 4 weeks ago (when having a brew there whilst skiving off work for half an hour!) and it is obviously an escape (it bears a small metal ring on the right leg), happily allowing you to walk right up to it, however, it is an educational bird and if you happen to be around the Canada's in the car park at Pennington, why not take a look for yourself!
The identification and separation of the Lesser Canada Geese 'group' can be very difficult with much integration, but this bird appears to me more like a Taverner's (taverneri) Canada Goose, although it has to be said I have little practical experience here and until afew years ago was blissfully ignorant of their seperation!
The bird is obviously much smaller than the accompanying nominate canadensis, with a very dark brown breast, concolourous with the rest of the underparts and a slight white 'neck collar'. The neck is rather broad (and not as narrow as I'd expect a parvipes), with a short and incomplete but obvious and quite broad partial 'chin strap'. The head shape is obviously squareish with a rather steep forehead, although I felt the bill was quite well proportioned and not particularly small or compact.
Either way it might not seem a particularly interesting or certainly exciting bird, but considering there wasn't much else around at Pennington today, it was the best I could muster!
