So let’s see: iridescent greens, blues, cobalt, purple, violet, bronze, ultramarine, crimson, burgundy spotted with white, black, and vermiculated gold; we could just as well be reading a list of exotic colours on an artist’s palette as descriptions of Wood Duck plumage – a dandy’s colours for sure. See for yourself; click on the image below.
The females above are noticeably subdued in their plumage compared to the drakes, but being the sole incubator of the eggs, and the guardian of the young when they first emerge from the nest, it makes sense to be less eye-catching to predators. It’s all about remaining inconspicuous, and not drawing unwanted attention. This is a common evolutionary adaptation among many bird species, and among North American ducks nearly all species show this strong sexual dimorphism. Wood Ducks happen to be one of the species that push these male/female differences to the extreme. While it is the drakes that catch the eye on a first look, both females and males are worthy of close scrutiny that reveals the real complexity and subtlety of the colours of both sexes. Let’s start with a closer look at the females.
Most species of female ducks are relatively drab in colour, often a mixture of browns, buffs, and tans, but our Wood Duck above shows some iridescence both on the top of the head, and in the shoulder feathers (scapulars) spreading out below the neck. Taking an even closer look at the scapulars we see the subtle, but beautiful colours that we might otherwise miss when seeing a female perched alongside her fancier mate.
Wood Ducks are unique among North American duck species. They are the sole representative on the continent of their genus, Aix (Greek for waterbird). In fact, the Aix genus contains only two species worldwide. The other is the Australasian Mandarin Duck – another contestant in the “dandy duck” stakes. Both are part of a larger group called the perching ducks. Wood Ducks certainly live up to that classification. They are often seen perching along the water’s edge on logs and in sometimes in trees.
There’s a certain irony, however, to the dramatic sexual dimorphism we see in Wood Ducks. It’s the drabber females’ choice of mates that drives the evolution of the spectacular male plumage. Pairs are seasonally monogamous, i.e. they pair-up anew each year, but because the males play no part in rearing the young (more “dandy” behaviour?) their breeding success is more strongly determined by their ability to attract a mate. Therefore, the bolder the plumage, which indicates to the female readiness and suitability of the male for breeding, the more chance the male has of being selected and passing on his genes to the next generation. Other species of birds in which the males do assist with rearing the young are frequently less sexually dimorphic. Here’s the drake Wood Duck.
The colours above need no more description, but it is worth noticing the rakish crest that flows down the back of the head. The female has one too, and among the dabbling ducks in North America (Mallards, wigeons, and teals etc), the crest sported by the Wood Duck is unique.
The gradations of colours here on the head are quite striking in close-up. No doubt they’re just what an interested female is looking for.
And while all this fantastic plumage is in pursuit of one thing – passing on the male’s genes to the next generation, Wood Ducks also need suitable habitat to breed successfully – marshy lakes and ponds with lots of surrounding vegetation. Oh yes, and one more thing; they need nest cavities. Before the forests of North America were extensively cleared, and the old trees that contained natural cavities from broken branches and abandoned woodpecker holes were cut down, Wood Ducks were numerous. However, by the late nineteenth century there were real fears that the Wood Duck would go extinct from the combination of habitat loss and over-hunting. After the Migratory Bird Act of 1918 ended the legal hunting of Wood Ducks, the species recovered rapidly. Concerned conservationists also helped them along by providing nest boxes to replace the natural cavities that had been lost in forest clearing.
The best place locally to see lots of Wood Ducks is Burnaby Lake at Piper Spit, and it’s no coincidence that at this location you’ll also see many nest boxes put up specifically for Wood Ducks. Although there are many nestboxes at Burnaby Lake, there may not be enough for all the ducks needing one. There are frequent incidents of egg-dumping here when more than one female lays her eggs in a single nest box – up to thirty eggs in a one box. Now not all the eggs will hatch in these conditions, but for a female that can’t find a nest cavity of her own, it seems a good strategy to ensure that at least some eggs produced by the female will hatch.