Scaup or hybrid?

That’s the question being asked by a number of birders after at least a couple of locals have voiced their opinion to the effect that the Ditchford Gravel Pits individual, currently present on Wilson’s Pit, is not a 100% pure Scaup. It has been there since its discovery on 16th January and I caught up with it last weekend (22nd) before going to see it again this morning.

The anomalies being cited are a) ‘small’ size, b) lack of prominent pale ear-covert patch, c) black on the bill tip not restricted to the nail and d) a pale subterminal band to the bill.

Have a look at the best of a bad bunch of digiscoped photos, below. With regard to the size it’s a little larger than a Tufted Duck, with a larger head and slightly bulkier body but it’s fractionally smaller than most Pochard present. The pale ear-covert patch, which develops in late winter and is variable, is present but not prominent (see first photo).

First-winter female Scaup, Ditchford GP, 30th January 2012 (Mike Alibone)

Let’s see if it becomes more obvious with time (assuming the bird stays, of course!). With regard to the pale subterminal bill band, it’s actually quite narrow, diffuse and slightly lighter than the overall bill colour and it’s not too uncommon for Scaup to show this contrast against the black nail. The latter colour also extends on to the bill tip, fanning out either side of the nail, but it is restricted to a small area (see second photo).

First-winter female Scaup, Ditchford GP, 30th January 2012 (Mike Alibone)

Presence of this feature – when more extensive – is often quoted as an indication of hybridisation but it is normal for first-winters to show a variable, though small, amount of black in this area. The white feathering around the base of the bill is tinged brownish and not particularly extensive.

These last two features point to immaturity and I think this bird is a first-winter female (first-year male would be expected to show some upperpart vermiculations and a darkening of the head and breast by now). All other features (overall shape, proportions and especially head shape) are fine for Scaup. So I don’t have any problem with this being a perfectly normal first-year female Scaup … but I’m willing to listen to any other arguments against this to learn in the event that I am wrong 🙂

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