Got onto the reserve at about 3 pm, and had a look at the birdfood before I went off to the Frith Hide. There were good views of the large gulls, mainly Herring, but also Lesser and Great Black-backed Gulls. The juveniles were particularly intriguing. The sub-adult Lesser had a good black stripe at the tip of the bill. The young Great Black-backed was particularly scaly.
From the Scott hide, different views of the Gulls, and many Cormorants. One Cetti's warbler close to the hide.
Back to Dennis' hide, and very good views of the drake and two duck Smew, Mergellus albellus, together with the related Goldeneye, here two drakes and three duck, all in one telescope view.
Why are there so many more female Smew than there are males? Even in German winter quarters, there are only 45% males, and in Britain females greatly outnumber males. The answer is given in a Birdworld article: "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." Generally when in England they are traditionally found South of the Wash (this may be less true nowadays), and may be temporarily driven over from Holland in severe episodes of winter weather.
The Smew, Mergellus albellus, is one of the smallest members of the sawbill group of duck. Like the other Mergansers in the main genus Mergus, and also in the tribe Merginae, the bill is serrated. In the winter and early spring, the Smew's diet is mainly fish, either on salt or fresh water. On the breeding grounds, when the birds move from the rivers to the lakes as they unfreeze, the diet changes to insects. In November, when the insects die or drop to the bottom of the lakes, the diet changes abruptly back to fish.
The female is most easily recognised at distance by its flattened shape, and the obvious white cheeks. Next the red cap is fairly easily picked out, against the generally light grey bird. The narrow white wing bar can be seen at rest, and can be seen as one of the three white sides of a square when the wing is extended - or that's what it looked like to me.
The male is obviously primarily white, with black lines and greyer areas on the flank. The shape is again quite distinctive, particularly the steep forehead. The bill is particularly delicate.
On the breeding grounds the birds use dead trees, often holed by Black Woodpeckers for nest-sites. They readily adapt to nest-boxes. Threats to the population include habitat loss particularly affecting nest-sites such as logging and river canalisation, oil pollution, and hunting while on passage.
