One Slimbridge collection bird (left), one wild bird (right):
The collection bird is older, and so is greyer. It also (even in my lousy photograph) clearly possesses a brighter yellow iris. In comparison the wild bird has a dull iris - indicative of a first winter bird.
Although plumage and head shape were always available for inspection, I was fearful that the bird would keep its most prized distinguishing feature tucked away for the duration of my visit. However, I'm pleased to report that it did raise its head and have a stretch. It was snowing onsite so the photographs are as good as I could comfortably manage. The first image shows the white wing bar trailing into grey through the primaries.
As I was leaving, I photographed it swimming about:
I also decided that the male Mandarin Duck on the Pen was fair game for a tick. The Slimbridge wardens seem content that it's wild.
In the morning I popped into Coombe Hill Meadows and added a few bits and bobs to my year list (which I'm not interested in!). The most pleasing (of nothing spectacular) were Treecreeper and Great Spotted Woodpecker. 55 now.
Also onsite - from the Grundon Hide - were over 100 Greylags, a few Canada Geese, a distant flock of Wigeon (couple of hundred birds perhaps), two Lapwing, three Buzzards and a fly through Sparrowhawk.
I was pleased to see that there is now a longer raised walkway allowing access to the Grundon Hide from the canal towpath. This should mean that when the fields next flood, the hide will still be accessible.