Yellow-billed Pintail x Laysan Duck Anas georgica x Anas laysanensis

This bird was on a pool containing just 6 ducks and a Mute Swan. The other ducks were 2 Shelduck x Wood Duck hybrids and up to 3 Ferruginous Duck x Tufted Duck hybrids. This bird was much warier than the others and I initially saw it only at the far side of the pool. It briefly came close, but keeping close to and below the overhanging building so only in poor light. At the time I considered Yellow-billed Pintail but was not sufficiently familiar with that species to go any further, although I had doubts about its purity, partly due to the unimpressively long tail. On checking references later I discovered that females do have relatively short tails but there are other problems: the internal markings to the body and scapular feathers are not present on Yellow-billed Pintail and the extent of black on the culmen is too great. The pale eye-ring is abnormal too, and there seems to be a very slight hint of an upcurl on the long central uppertail-coverts. Also the legs seemed to be yellowish. All of these anomalies could probably be explained by hybridisation with Laysan Duck, but there may be other possibilities?

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putative Yellow-billed Pintail x Laysan Duck hybrid, River House Restaurant, Stirling (Stirlingshire, UK), 29th December 2013