An old acquaintance: Gralla's intersex Mallard

"intersex" mallard
Stockente / Mallard (Anas platyrhynchos) | "intersex", Gralla, 10.8.2015

While late summer is a great season for birding, with fall migration in full swing (17 species of shorebirds today in Seewinkel!) and plenty of topics one could write about, I just want to report shortly about an encounter I had yesterday, when birding around my hometown Graz.
At the famous birdwatching (and duck-feeding site) in Gralla, along river Mur, I found a bird that I'm irregularly observing since nine years now. I wrote about this and similar birds in the area already here (in German) and posted photos of this exact bird here, here and here.
So called "intersex" Mallards (Anas platyrhynchos) are females, which develop male (plumage) features as they're getting older or when having a troubled hormonal balance. The reasons for this are not fully understood. While it seems that there hasn't been any new research on this topic, a quick google search revealed some new things dealing with intersex birds and plenty of new photos on the net. Look here.

This time, I couldn't take perfect images of the bird, but the first ones I got at a time of the year, when the bird should be in eclipse plumage, like all the other mallards around. Surprisingly, it was already much further advanced than the others, with a largely green head etc.

In the course of the years, the bird developed a more and more perfect male plumage, but with the eclipse feathers on belly, flanks, scapulars and head, it's hard to judge if there has been any advance now. Some female-like spots in the rectrices remain, but the tail curls are already perfectly masculine!

"intersex" mallard
Stockente / Mallard (Anas platyrhynchos) | "intersex", Gralla, 10.8.2015
"intersex" mallard
Stockente / Mallard (Anas platyrhynchos) | "intersex", same bird as above (checked by bill pattern) in fresh breeding plumage, Gralla, 21.12.2008