Smew (Mergellus albellus)


Smew (male)

Measurements: 38-44cm long.

ID: Male quite unmistakable. Female distinctive, with grey plumage but a reddish-brown head with contrasting white cheek.

The Smew has much in common with the Goldeneye, despite the two looking very different and not being particularly closely related. Their most striking similarity is in their breeding ecology: both use holes in trees as nest-sites, particularly those made by Black Woodpeckers; both use down as virtually their only nest material; and both require the presence of large coniferous trees beside sheltered, productive lakes, where they feed on rather similar foodstuffs. Perhaps not surprisingly, there are several records of the two species hybridising.

There are differences, though. Where the Goldeneye has a wide distribution, the Smew is much more restricted, breeding in Europe mainly in Sweden, Finland and Russia. The Smew also has a marked preference for quiet backwaters, flooded forest and other sites with plenty of tree cover, being less drawn to large, open waters. And the Smew has a slightly more restricted diet; in the breeding season it favours insect larvae, and for the rest of the year, particularly in winter and early spring, fish are the major component of its diet. The Smew has sharp serrations on the side of its long bill to hold on to these slippery customers, a specialisation the Goldeneye lacks.

In the winter Smew migrate south, the females and immatures travelling further than the adult males. In the early spring they begin to return and the sexes mix, triggering much display. The Smew’s most obvious posture is the “pouting display”, in which the male puffs out its chest and retracts its head, keeping the bill horizontal.

Article from Bird Watching magazine (2005)

The waves made by the Smew in Britain are comparable to those made by a noisy but peripheral human pressure group, the sort that can drive the political scene. There is a similar imbalance: the numbers are low but their profile is inordinately high. We take notice of both Smews and those who wish to legalise soft drugs, for example, even though the statistics suggest that we could forget all about them. Insofar as the duck is concerned, everyone seems to embrace the Smew as very much a British bird, albeit quite a scarce winter visitor. And yet the actual number we receive each year, which has recently been estimated at 370 birds, is pitifully small. Some day soon, the annual count of bejewelled Asian long-distance migrants, such as Yellow-browed Warblers, is going to eclipse the equivalent tally of Smews. But all our British bird books will keep the Smew and its picture in place, while to find Yellow-browed Warbler you will have to look in a more specialised tome.

The truth is that the Smew is not very British. Even the remnant we do receive is second-hand, so to speak. Smews travelling south-west after breeding tend to settle for the winter in Holland, on a huge lake called the IJsselmeer, where they stay if they can, and may number 10,000 birds. It must then take a surge of freezing weather to drive decent numbers of Smews over the North Sea or English Channel to Britain. The first arrivals are usually in November, but many do not stumble over here until January or even February, ensuring that their stay is startlingly brief.


Smew (female)











And as if to rub in their sparing patronage, Smews don’t even send us many of their best. Although the females, and the similarly plumaged first-winter immatures, are distinctive and dapper birds, they cannot compete for sheer looks with the males. A true Smew is a male Smew, with its authentically snow-tinged plumage and smart black blobs and lines that break up its outline. Yet we receive many fewer of these than females and immatures. The reason is a phenomenon known as differential migration. In many species of birds, different age classes of birds have different migratory profiles. Most typically, adult males undertake the shortest journeys, staying as close as possible to the breeding grounds so that, when the time comes, they can sprint quickly to occupy their high latitude territories. Females also tend to be smaller-bodied than males, and potentially suffer in competition with them, so they migrate longer distances, keeping them away from the males and allowing them to nestle in more gentle climates. But the result of this differential migration is that we, at the far end of the Smew’s migration, are starved of seeing the handsome males. The migration is differential, and also discriminatory.


And of course, the core of a Smew’s life, its breeding season, is also lived in faraway places – in the northern taiga to be exact. The taiga is the complex of vast, mainly coniferous forests and wet bogs and marshes that dominates the land south of Eurasia’s bitter tundra zone. It starts well to the north of us, and our nearest breeding Smews are in northern Sweden, Finland and European Russia. They are scarce there, with quite exacting habitat requirements. They need small, productive, still or slow-flowing pools surrounded by forests of large trees, including dead ones. And they also need a very specific property developer to be present, the Black Woodpecker. This big, chisel-billed excavator is often the only maker of holes large enough for these ducks to use for their nests.


People are often surprised when they learn that ducks can nest in holes in trees. But the habit is quite widespread: among British ducks Mallard, Mandarin, Goosander and Goldeneye are all frequent or compulsive users, so the Smew is actually a member of a small club. And, if clubs can have cliques, there is no doubt that Smew and Goldeneye form one of their own. These two species overlap considerably in their breeding ecology, so much so that both competition and confusion may be rife where the two occur together. Both, for example, use still freshwater lakes among forest; both eat similar types of food, and obtain it by diving; both use holes of approximately the same size for their nest; and both are unusual in lining the coarse floor of their holes with copious amounts of down. With such a confluence of needs and activities, it is not surprising that these birds sometimes get in each other’s way, so to speak.


You might be surprised to hear it, but in confrontations between the two, the Smew is generally dominant over the Goldeneye, although it is slightly smaller. It quite frequently usurps a Goldeneye’s nest-hole, even when the former tenant has already laid a clutch of eggs inside; it places its own right on top of them. However, there are many reports of mixed broods, and one might assume that, in the darkness of a nest-hole, it might be quite difficult to be selective about what you sit upon.


That’s not the end of the intrigue, either, because, as often happens when demand for nest-holes greatly outstrips supply, Smews sometimes resort to a little intraspecific brood parasitism – in other words, Smews sometimes lay eggs in the nests of other individuals of their own species, adding to the burden of the incubating foster female whilst clandestinely increasing their personal productivity, possibly because of a lack of alternative nest-sites. This can lead to greatly increased clutch sizes: 14 eggs, for example, instead of the usual 7-9.  Another, more surprising twist to the Smew’s breeding behaviour is its quite regular habit of hybridising with its nemesis the Goldeneye; odd, because the two ducks are not particularly closely related. Yet, in terms of their remarkably similar breeding ecology, perhaps it should be expected.


Another aspect of the Smew’s breeding lifestyle that might be a surprise to some is its summer diet. Smews are members of a group of ducks known as “sawbills”, which are characterised by possessing sharp serrations along each side of their long, thin bills. These serrations traditionally help the birds hold on to slippery fish, but in summer Smews evidently don’t use them for this purpose. Instead, they forage primarily for insects and their larvae, plus a few crustaceans and amphibians; they obtain these by diving underwater. Water-beetles, caddis larvae and dragonfly larvae are particularly important foodstuffs, and the former may account for 60% of the entire diet. It seems that the birds concentrate on this relatively slow-moving prey instead of bothering to pursue more slippery, awkward customers.


Once the birds leave their breeding areas, however, from September onwards, their diet does change. Smews move into more open waters, and here they do concentrate on catching fish, in respectable sawbill fashion. However, being small ducks, they tend to avoid the fast-moving or turbulent water often fished by other sawbills, in favour of sheltered bays and margins, but they can adapt to both fresh and salty water. Ideally, this should be shallow, no more than 6m deep, because the birds themselves only undertake short, shallow dives, rarely immersing deeper than 4m. This rapid smash and grab diving is somewhat symptomatic of the bird itself; it is a restless creature, forever swapping sides of lake, swimming quickly about, or taking flight in loose groups to transfer between water bodies.


As you might expect, the sort of fish favoured by Smew are small species between 3cm and 6cm long, although there is one remarkable record of a Smew consuming a monster 29cm in length – that’s three-quarters the length of the bird itself! The freshwater cast list includes sticklebacks, minnows, trout, gudgeons, pike and eels, while in saltwater the Smew will catch herrings and plaice and sand-eels, among a whole range of both bottom-dwelling and free-swimming species. So long as they are the right size, the Smew, it seems, will take them.


Every so often, an exciting feeding phenomenon will take place – a communal fishing expedition. When Smews do this they swim along in a line, like a group of beaters, in order to herd fish in a particular direction so that they can be concentrated into shallow water and caught more easily. The birds often synchronise their dives, to perform a co-ordinated flush, and when moving along a flock can move so fast in one direction that the birds at the back have to make short flights to catch up. When fishing communally, Smew flocks are much more concentrated than usual, with the birds swimming very close together. Where Smews are abundant, up to 750 birds have been seen taking part in one of these mass movements, which must make for one of the great sights in birdwatching.


The trouble is, though, that we just don’t see such things on our waters. We cannot muster 750 birds in the entire country. Hardly anyone in Britain has seen a group of Smews fishing together, because it’s hard enough to find anything that even constitutes a group. Such wondrous sights will probably never be seen here, particularly if global warming enables the birds to winter progressively further north.


To a Smew, you see, Britain is a peripheral part of its range. We don’t figure much on its radar. The odd thing is that it does feature, quite prominently, on ours. For the moment this gorgeous duck’s place in British hearts, if not statistics, is assured.






The European breeding population is about 2000 pairs, with a further 7000 -15,000 in European Russia. The total wintering population is some 80,000 birds.


The breeding population has declined because of deforestation and because of increased predation by mink.


The Smew also breeds right across Siberia, and some winter in China, Korea and Japan.


Besides the Dutch IJsselmeer, large numbers of Smew also winter on Szczecin lagoon in Poland, in the Baltic Sea, and also as far south as the Black and Caspian Seas.


In late winter, flocks frequently perform communal courtship, with groups of 2-7 males displaying to 1 or 2 females.


In early courtship, the male attempts to circle around a female. At this time there is much head-shaking and wing-flapping.


Later on, the Smew’s most distinctive display can be seen, which is known as “pouting”. The male keeps its head horizontal (unlike in many duck displays) and moves it back and forth regularly, reaching back until it is over the mantle, but not going further than above the breast.


The birds often migrate back in pairs. Their pair-bond will last for a season only, and breaks up as soon as the female begins to incubate.


Smews begin breeding in mid-May. Besides using holes in trees, they are also exotic users of nest-boxes.


They lay 7-9 eggs, which are incubated for 26-28 days. While the females are incubating, the males begin their annual moult.

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