Winter bird movements (Focus - January)

Winter can be a tough time for wildlife and while a number of mammal species will hibernate, many birds deal with poor weather by moving to lower ground or even to a different country. The storms and snowfall of December got many thrushes on the move, and in the weeks following there appeared to be many more blackbirds, redwings and fieldfares in the local fields and hedgerows. It is not just the cold temperatures that they are escaping; a blanket of snow will make food inaccessible forcing them to move to clearer land to feed. Redwings and fieldfares will already have travelled from Scandinavia and Russia to find a milder winter and will keep moving to keep clear of the worst conditions. Similarly, there are increased numbers of coots, mallards, and tufted ducks on Fonthill Lake, where they will spend the winter.

This is all normal but what makes things interesting is when there is real dearth of food for birds in their normal wintering areas. This might be because the food crop (for example acorns, beech mast or fruits and berries) has failed or a species has had a population boom after a good breeding season. This is when an irruption can occur, and huge numbers of birds move to parts of Europe where they are not normally seen. A recent example of this was during the winter of 2017/18 when unusually large numbers of hawfinches were seen throughout the UK. They made a rare sight in the beeches around Fonthill Lake and even popped up in Tisbury gardens. This year it seems to be the turn of the brambling to visit us in large numbers, presumably because of a failure of the beech mast crop on the continent. After reaching the east coast in late September, they had soon spread across the whole country and by the end of November seemed to outnumber the chaffinches in some local beech woods. (You can see this movement graphically on eurobirdportal.org).
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It has been a particularly poor year for acorns which will hit jays which favour this as their winter food, normally burying thousands in the autumn for later retrieval. They may travel several kilometres from their home range looking for acorns and will be more visible than usual as they do so. But if the acorn supply is exhausted, they too will be on the move. The classic irruptive species is the waxwing, a bird rarely seen in the UK apart from during one of their irruptions which only occur once every 10 years or so when flocks of a hundred or more may be seen. Who knows what this winter will bring?
by Andrew Graham