Compare the tail to drake mallard (top right) and hen mallard (bottom). Mule duck, as have always heard them called, had hen-looking tail feathers, but had the distinctive drake curls...
Compared to a drake mallard (top), the mule duck wing looks like a drake mallard at a glance, but note that the white wing bar above the speculum on the mule duck (bottom) extends into the terial area, as characteristic of hens
Now look at the head. Mule duck (middle) has the yellow bill color of drake and some green in its head. The bill has the black saddle characteristic of a hen and teh lower part of teh head looks suzie too.
Looked under it's tail and it was definitely a hen duck. Estrogen is a precursor of testosterone. Don't know why there was a hormonal imbalance (heard someone once say it was menepausal-like). At any rate, it was a hen I shot for a greenhead
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