Tuesday, 17 August 2010

Old gravel pit a welcome stopover

Over recent weeks there has been a pleasant inevitability to my weekly visits to the old gravel workings. Each week, as I approach the shallow fringes of one particular pool, I invariably see the white-flash of a Green Sandpiper flicker out low across the water and away. On some days there may be two or even three of these delightful little birds feeding together. Watching them jink away, all white rump and dark body, they are reminiscent of oversized House Martins. These sandpipers are most likely passage birds, already working their way south on an autumn migration that will take them to a wintering area that extends from western Europe, down around the Mediterranean Basin and into sub-Saharan Africa. Some do overwinter here, often returning to the same favoured spots, and I have come across them on occasion at that time of the year.

The birds that I have been watching recently will have come from breeding grounds that stretch across the boreal forest zone, north to the edge of the Arctic Circle and south to those countries bordering the Baltic. Breeding does occur in Britain but it is a very rare event and largely restricted to the North of Scotland. Unusually for a wader, Green Sandpipers do not nest on the ground but instead make use of old pigeon nests and squirrel dreys. This might explain their breeding season preference for coniferous forests dominated by spruce or pine and with access to small water bodies.

Like certain other species using these northern breeding grounds, the autumn migration starts early. In fact the Green Sandpiper is probably the first wader to be on the move come autumn, with the first returning birds reaching Britain in mid-June. Peak numbers do not appear until July and then the passage continues through into late September. These early arriving birds will be adults, most likely females who have left their unfledged young in the care of their mate. By late July or early August, the first of the juveniles have reached Britain, stopping to feed on freshwater lagoons and old gravel-pits with unvegetated muddy fringes. Later in the year, when we are probably looking at birds that are going to overwinter here, the birds become more solitary in habits, often moving away from still water sites to those where the water is in motion. Presumably this is linked to the better feeding opportunities available on rivers, streams and watercress beds during the winter months, although it is worth noting that the birds will return to lagoons and gravel pits each evening, when they retire to roost. The presence of these delightful birds alerts me to the approaching autumn and a season of change.

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