Thursday, 3 January 2013

A waxwing winter

It has been something of a waxwing winter, with good numbers of these stunning birds arriving from the boreal forests of Scandinavia and western Russia. That they arrive here at all is very much down to their irruptive habits, with birds moving en-masse under particular conditions. In some years, very few waxwings are to be found in Britain during the winter but in others many thousands of birds may arrive. The size, timing and location of these arrivals are determined by the success or otherwise of the breeding season and the availability of rowan berries during the autumn months that follow. Rowan is the favoured food, so in years when the crop has been poor the birds are forced to move on elsewhere and it is these movements that bring them to our shores.

The autumn saw a good arrival in Scotland and northern England, with birds filtering south as the berry crops there were depleted. However, even here in Britain many berry crops have been poor this autumn so the waxwings have tended to be rather mobile. While this means that they have been turning up in lots of different places, it also means that they have not tended to stay in one place for long, much to the frustration of those birdwatchers and photographers hoping to catch up with them – there is little that makes a more festive photograph than a waxwing on a berry bush! One of the quirks of the winter distribution of waxwings is the association with industrial estates, new housing developments and supermarket car parks, all of which are places where berry-producing shrubs are used as amenity planting.

Another interesting aspect of waxwing behaviour is its alcohol tolerance. Berries are rich in sugars and fats and are a valuable food source during the autumn and winter months. Over time, however, the sugars in the berries begin to ferment and alcohol levels increase. For any bird that eats a lot of berries there is the potential for drunkenness and the resulting impairment of normal activities, like flight or vigilance for predators. Those species that specialise on feeding on berries, like the waxwing, are better able to metabolise alcohol. In fact the alcohol tolerance of the waxwing is reputed to be equivalent to an average-sized man drinking more than two and a half pints of 5% beer every hour from dawn until dusk! By comparison, the equivalent figure for the greenfinch, which feeds on berry seeds rather than the pulp, would be just half a pint each hour. If you have a berry-producing bush or shrub in your garden with berries still present then you might just get a visit from these Nordic nomads.

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