Intersex Mallard (?), Vancouver

By Charlie February 17, 2009 18 comments

Yesterday I posted a short series of photos of a male Varied Thrush Ixoreus naevius I took in Vancouver’s Stanley Park two days ago. Whilst the Varied Thrush was the “bird of the day” the bird that’s caused me the most head-scratching is the Mallard Anas platyrynchos in the photos below. When I first noticed it (at distance) I immediately thought “hybrid” but when I got much closer - down to a few feet finally as it scrabbled with other Mallards for food - I was far less certain. I’m wondering instead if this might be an ‘intersex’ female - a female with low levels levels of oestrogen (UK)/estrogen (US), the hormone responsible for the development of female secondary sex characteristics? Low levels can apparently result in female birds developing male characteristics…

 


strange mallard

strange mallard

 

Though this bird does look a little like some of the hybrid Mallard x American Black Duck A. rubripes I’ve seen (we have photos on the blog at Hybrid Mallards), it’s clearly not. Besides is that particular combination likely (or ever been recorded) on the west coast?

If not a hybrid is it a “manky mallard” (a domestic type crossed with a pure Mallard)? If it is a “manky” it’s unlike any I’ve ever seen, and I’ve been looking at hundreds over the last few years: domestic x wild Mallards crosses typically show some characters of the parent domestic bird’s genotype (white bibs or unexpected plumage tones for example, and are often structurally different from wild Mallards).

No, what it appears to be is a male/drake Mallard - note the white collar, ‘curly’ black uppertail coverts, chestnut chest for example - with an abnormally brightly-coloured female Mallard’s bill and elements of female type cheeks. The bill pattern is typical of a female mallard (note the ‘normal’ female in the foreground of the top photo and compare the bills), the speculum is pure Mallard, the wings appear to be exactly what you’d expect for a Mallard and the structure of this bird is no different to the other Mallards all around it.

 


strange mallard

strange mallard

strange mallard

 

Could the explanation perhaps lie in a delayed moult from the eclipse plumage that ducks wear in the late summer? The feathers all look fresh to me: these photos were taken in February, and surely if the moult had been delayed over the winter for some reason there’d have to be some heavily worn feathers visible? Besides even in eclipse plumage male Mallards retain their normal greenish-coloured bills (albeit a little subdued), not develop bright orange and black ones.

My (untested) feeling is that this bird has to be a female with low oestrogen levels, as the ‘default’ position for mallard plumage appears to be that worn by the males…”Sexual dimorphic plumage in waterfowl is apparently estrogen dependent. In short, the default plumage is the drake plumage and the presence of estrogen causes the hen plumage we associate with female birds. If a female bird is completely unable to produce estrogen, she’ll instead show male plumage.” [see Comments below].

The more you look around the net the more examples of this natural phenomenon you find. None/few of these web examples appear to be scientifically verified, but aviculturalists have known for many years that older females of a number of species can show male plumage features (see, for example, http://www.ias.ac.in/jarch/jgenet/39/503.pdf which opens with, “In domestic fowls, castration of hen-feathered cocks and ovariectomy of hens leads to the assumption of typical (male) display plumage at the next moult”).

 

Local birders visit Stanley Park most days, so perhaps this bird has already been noted and an explanation offered. If anyone can provide me with a link or a contact email address I’d be very grateful. Alternatively perhaps you’ve seen a Mallard like this before and have the answer - please leave a comment in the box below. It may seem a peculiarly esoteric conundrum to get worked up about, but I would really like to understand (if possible) what’s going on with this particular Mallard…

 

Photos copyright Charlie Moores 2009

 

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About the Author

Charlie

Charlie

Charlie has birded all over the world for twenty years, lives in the UK, and is a freelance writer/photographer/editor - oh, thinking about it whatever you need he'll do it. Blogging with 10,000 Birds is like chatting to hundreds of friends every day and suits him perfectly.

18 Responses to “Intersex Mallard (?), Vancouver”

  1. Interesting! For us, its a privilege to spy any mallard - manky, regular or strange, so its good to see such a detailed description of all aspects of the bird!

    As an aside, why are all female ducks of all kinds such a boring brown?!

  2. Hi Flowergirl

    Female ducks are brown (and beautifully marked really) because they’re the ones that have to sit on eggs in one place for long periods of time and the colours help them blend into the native grasses, rushes, reeds etc they nest in so that predators don’t spot them. If they were brightly coloured like males they’d make very easy targets - and we’d have less ducks around than there are now!

    Cheers

  3. I don’t have experience with this, but recently an “odd Mallard” was sighted at the Cornell Lab of Ornithology’s pond (here’s something I’ve found very helpful when viewing odd birds: it’s good to have a building full of birders and ornithologists around). Here’s the post to our local listserve that followed:

    “There is an intersex female Mallard hanging out at the pond at Sapsucker Woods today. It’s kind of a cool bird. It’s an old female Mallard that doesn’t have enough estrogen to grow a normal female plumage. It basically looks like an odd male with a pale cheek, green behind the eye, dull yellow bill, chestnut chest, but lacks the pure gray body. Some people are inclined to think these individuals are hybrids, as that is often the default assumption for an odd-looking bird.

    I’ve found intersex females are actually fairly common in flocks of Mallards in winter. They are easy to pick out if you sort through Mallards this time of year, because all the drakes are in their “perfect” plumage and will not have any retained eclipse plumage past November normally.”

    Maybe this explains the Vancouver bird?
    -Mike

  4. Yupp, intersex female. There was (still is?) a female close to Greifswald that looks almost exactly like your bird.

  5. Couldn’t it be just eclipse plumage?

  6. Hmmm… why assume this is a female? Maybe it is an old male without enough testosterone to grow a fully male plumage? Which plumage is the ‘default’ anyways? Hmm…

  7. Mike: thanks for this info - it’s amazing what’s out there on the net of you know where to look!

    Jochen: …and it’s always amazing what turns up in Griefswald :)

    Nick: My thinking is that an old male would have a dull green bill (duller then usual) rather than a very bright female-type bill - but I’m no expert on these things: maybe it is a male? Anyone care to comment?

  8. Nuno - the bill rules out eclipse, Males in eclipse retain the ‘male’ pattern.

    Charlie - You may be right, but it depends on the control of bill color, and which is ‘default’. Only solution to know for sure is to sex the bird by gonads. Unfortunately that’s a very invasive procedure. Fortunately, Mallards are tasty (just kidding, it is possible to do it non-lethally).

  9. Nick - great question! I did some lunchtime reading and found that sexual dichromatism (where males and females of the same species have different colors/markings) in Mallards (and the rest of the Anseriformes) appears to be estrogen dependent.

    Experiments showed the presence of estrogen leads to “dull, henny (female?like) plumage, while its absence results in a bright, cock (male?like) plumage. In both sexes, removal of the gonads results in assumption of the bright, cock plumage. Estrogen supplements to either males or females during the molt results in assumption of the dull, henny plumage, whether or not the gonads are present. In contrast, testosterone treatment does not affect the resulting plumage in either sex. In these species, therefore, the bright coloration of male feathers does not reflect male hormonal status. Instead, the brightly colored cock plumage is the “default” condition that results from the absence of gonadal hormones”.

    For more: Rebecca T. Kimball and J. David Ligon. Evolution of Avian Plumage Dichromatism from a Proximate Perspective. The American Naturalist 1999 154:2, 182-193.

    Charlie, you’re right: amazing what’s out there, not only if you know where to look, but when you have the time to delve into it!
    -Mike

  10. Fascinating! That’s exactly the type of paper I was hoping to find. Thanks!

  11. So what you’re saying is this is a female with low estrogen levels rather than high testosterone levels? I wonder why the bill is such a bright orange rather than either a dull orange or a dull green? Fascinating indeed. Thanks for the comments so far everyone…

  12. Hi All, I’ve updated elements of this post to reflect the fact that I’ve been able to find time to do some research (ie Google). Whilst the observation of an “intersex” bird is new to me, aviculturalists have observed it in older birds for many, many years, and researchers have precipitated the condition by removing the ovaries (where oestrogen is produced) in younger birds.
    I’d welcome more comments of course….

  13. I have pair of Mallards on my pond in the UK. I obtained them as 3 week old ducklings. I have the opposite conundrum. He developed beautiful male plumage in the first Summer. They produced 3 lots of eggs - we had 30 ducklings, of which few survived.
    The parents stayed, as the ducklings that survived flew off.
    However at the end of the summer, the Male began to loose his plumage, and after a few weeks had ‘female’ plumage. He now has male plumage again. He has always had a dull beak.
    Your comments please.

  14. Hi Nicola. It’s perfectly normal for males to lose their breeding plumage in late summer. It’s called the ‘eclipse’ plumage and they purposely look dull (like females) because they moult all their flight feathers at almost the same time and become flightless - dull plumage helps to keep them camouflaged and safer from predators until the flight feathers grow back again. We’ve a post at http://10000birds.com/the-eclipse-plumage.htm which explains it in more detail.
    Cheers

  15. It is simply in eclipse, which does make for an interesting photo.

  16. Hi twitterbee - It does look like that but eclipse in Mallards is long passed by this time of year (usually by November, these were taken in mid-Feb), and if it was in eclipse (or coming out of eclipse given its plumage) it would have to be a male (for obvious reasons) but it would then have a male’s green-yellow bill. What this has is female soft parts with some male plumage features, which is why it seems to be an ‘inter-sex’ individual.
    Cheers
    Charlie

  17. Hi! I know this post is old, but I wanted to comment. I’ve been observing a lot of mallard ducklings in my local lake and watching them age. Some of the ducks you show with the odd drake coloration may actually be ducklings that are about six to eight weeks old. Our lake’s first batch of ducklings are about that age and all the future drakes have that color. Their color eventually comes in later when they get closer to breeding age.

  18. Hi Darlene. Thanks for your comment. This bird was actually photographed in February so was very much an adult. From what I’ve learnt it does seem that older females with very low oestrogen levels can produce this mixed plumage and I’m fairly confident that’s what’s going on in this case. All the best.

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