In the photo below – taken in Vancouver, Canada on September 31st – there are six ducks. So far, so straightforward – but how many species are there and what sex are they? One species – the Mallard, two males (drakes) and four females perhaps? Or a mixed bag of indeterminate mallard-like birds which could be mostly females with some odd hybrids or strange crosses paddling amongst them? In fact there are two species – and this small flock is comprised of four male Mallards with just one female, and one male Wood Duck. Really? Indeed yes, and for an explanation we need to understand a plumage phase that is typical of ducks (but does occur in some other birds too) called “eclipse”.
Feathers are incredibly important to birds. They are a marvellous form of insulation, they’re used by the birds themselves to identify their own species, they’re vital for flight, and they have evolved into a huge variety of colours and shapes used in courtship and sexual selection. Without them a bird would be an unclothed, cold, unattractive, indeterminate pink blob (and, to be honest, most birders would probably be looking at insects instead). Ducks, like most birds that spend most of their time swimming, also use their feathers to repel water: all of which means that ducks need to keep their feathers in tip-top condition.
Feathers are surprisingly durable, but over a season of migration, courtship, nesting, food-gathering, and child-rearing not UNsurprisingly they get very worn. The tips often wear away, whole feathers fall out, and the covering of closely layered insulation the birds depend on gradually breaks down and, like an old blanket, becomes increasingly threadbare. The solution is to shed the old feathers and grow new ones – the process of moult (or as North Americans know it “molt”).
Different groups of birds have evolved different “moult strategies”: raptors, for example, replace body feathers and wing feathers in a set order and over several years; many passerines (eg thrushes) keep their wing feathers into the second year of life but replace their body feathers in the first year. Ducks, though, shed most of their feathers twice each year, and in mid-summer most male ducks moult from the bright and colourful breeding plumage into a drab, female-like “eclipse plumage”. The reason for this is that ducks have a rapid but complete moult after breeding, dropping both body and wing feathers, and for a few weeks are completely flightless. Temporarily unable to escape predators by flying away, many male ducks have opted to do what the females do for most of the year and merge safely into the background (or, like eg Shelducks, gather in large flocks offshore or in the middle of large lakes).
Does this make identification almost impossible? In some cases it makes it very hard, but whilst moult into eclipse means that the bird’s feathers change, the ‘soft parts’ (ie the bill, legs, and eyes etc) stay pretty much the same (albeit duller in colour than during breeding). If we have a look at the photo again, it’s plain to see that even though only two of the Mallards in the photo are in breeding plumage and therefore clearly typical males (bottom left and top right) the two centre birds have the yellow-green bills of a male Mallard and not the orange and dark grey bill of the female (the first bird on the left). The two centre Mallards are therefore males moulting out of eclipse plumage back into the smart breeding plumage they will later use to begin the whole breeding process all over again.
Male and female Mallards Anas platyrhynchos
Why are all four males not looking the same by the end of September? It appears that older, more sexually experienced males regain their colourful breeding plumage quicker than less experienced birds – sometimes even before the flight feathers are fully grown: it seems that the headstart (or advantage) some males gain by developing colourful breeding plumage earlier than potential rivals can outweigh the additional danger of shedding their camouflage before being able to fly properly.
The contrast between the eclipse and breeding plumages is even more marked in a duck as exquisitely coloured as a male Wood Duck. Normally a riotous blend of iridiscent bronzy-green and chestnut-browns, in eclipse the male looks far more like the well-camouflaged female – and therefore less likely to be singled out for dinner by a predator whilst temporarily flightless. The male’s pinkish bill and white head-stripes, though subdued in colour, are still present though making separating the sexes not as difficult a task as might first seem. Both of the male Wood Ducks in the photos below were taken in Vancouver: the first photo is a closer look at the eclipse male seen in the group of Mallards above; the second a breeding-plumaged bird taken on a visit in May.
Male Wood Ducks Aix sponsa
All photographs copyright Charlie Moores