Tuesday, 3 January 2012

Beechmast is the key

Find a stand of mature Beech trees this winter and you have every chance of catching up with some Nordic wanderers. Beechmast, the seed of the Beech tree, is an important winter food for birds like Chaffinch and Brambling. The mast is rarely plentiful in the same place in successive years, so birds that feed on it tend to move around, often covering large distances until they find areas with a sizeable crop. In the case of Brambling and Chaffinch, such movements can see them arrive in Britain from breeding grounds spread across Norway, Sweden and Finland. The flocks that congregate elsewhere in Europe, however, invariably dwarf the numbers wintering here. For example, roosting flocks of up to 20 million Bramblings have been recorded in central Europe but here the largest tend to be limited to a few thousand individuals.

Over the last couple of weeks the stands of Beech at Holkham Park have attracted a sizeable flock of Brambling, while smaller groups have been reported at other sites across the county. Sometimes, where a stand of Beech sits alongside a road, the birds dice with the traffic, fluttering down to grab fragments of mast, smashed by the tyres of passing cars and lorries. Both species feed mainly from the ground in winter, a contrast to the summer preference for feeding on insects in the canopy of trees and shrubs. Both species have comparatively large bills, with that of the Brambling being the more robust of the two, and this may explain why Bramblings show a greater preference for the seeds of Beech than any of our other wintering finches.

Bramblings winter as far north as the availability of Beechmast will allow. In those years when the more northerly crops have been poor, the birds are forced to move further south and west in search of food. Movements can also be influenced by winter weather, since a covering of snow can make any remaining mast unavailable. A combination of a poor crop and heavy snowfall, can see vast numbers arrive in Britain and, to a lesser extent, Ireland. Our relatively mild winter weather offers more favourable conditions for the birds, even if we have relatively little Beechmast available compared to the Continent.

It is not until later in the winter that we tend to see Bramblings visiting garden feeding stations to take peanut granules and sunflower hearts, something that may result from Beechmast and other seed crops coming to their end. Although weekly observations from the BTO Garden BirdWatch survey show the first Brambling arrivals in gardens during October, the peak does not occur until late March of early April, before falling away steeply by the beginning of May.

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