12-Aug August's Passing Parade

As the breeding season for most birds has now come to an end, many are starting to move to their autumn or winter quarters, perhaps stopping off for a time en route in favourite feeding areas or occasionally being blown off course. Species such as grey and ringed plover may have nested in the high arctic, the latter perhaps even within 1000 km of the north pole. The arctic summer, so far north, is a very short one and ends in early August. Consequently, we start to see a small number of these birds passing through London. We may also see some warblers gorging themselves on blackberries, elderberries and rosehips in hedgerows. Prior to departure some even double their weight building up their reserves for the ordeal ahead.

The autumn migration is a much more leisurely affair than the spring one, when birds tend to rush to their breeding sites. It starts in mid July and generally ends in late October, with numbers just slowly increasing throughout August. Swifts may have begun to leave at the end of July but more usually it will be the beginning of August. By the end of the month most will have gone. Sometimes, in the first week of August, Londoners in some places may see more birds than they have all summer because so many are moving south. Swallows and martins are also on the move and occasionally large numbers can be seen passing almost at head height, all flying rapidly in a southerly direction.

Adult cuckoos, tree pipits and many reed and sedge warblers are all early migrants and may have already left. Young cuckoos tend to linger and some warblers even decide not to go at all. Birds such as terns, guillemots and razorbills all prefer to migrate along the coast. Not all these movements are south, with species such as bramblings and greenshank arriving here from various other directions.

Birds that may be seen in rather larger numbers may include grey plover, bar-tailed godwit, greenshank and knot. More rarely, large congregations of common sandpipers, spotted flycatchers and yellow wagtails have been recorded. Birds which are more likely to be encountered individually, or in small numbers, include turnstone, whimbrel, whinchat, pied flycatcher, redstart and perhaps a black, sandwich or little tern. Rarities recorded in recent years include the ortolan bunting, quail, ring ouzel, wood warbler, crossbill, stone curlew, dotterel, ruff, purple heron as well as some skuas and egrets.

Raptors such as Montagu’s harrier, honey buzzard, goshawk, osprey and hen harrier all make infrequent appearances in places such as Rainham marshes. A good range of rare gulls also visit the Staines reservoirs e.g. sabine, mediterranean, Caspian, ring-billed and yellow-legged gulls.

Different sandpipers are especially rewarding to look for in such unlikely places as Beddington sewage works. With their long, spindly legs and graceful movement they are reminiscent of stints. Some tend to ‘bob’ both their head and tail. Although not usually gregarious with their own kind, species such as the common sandpiper may now be seen in groups of ten or more. Others which do not breed in Britain tend to be seen in much smaller numbers and these could include the green, wood and purple sandpipers. Spotting the difference between sandpipers is not for the faint-hearted.

It can be difficult, especially with the added confusion of differently marked juveniles as well as their natural tendency to wander. However, the common sandpiper is often given away when it is disturbed – as it flies off in a burst of shallow wing beats and flicks its wings.. It also tends to fly low, twisting and turning, before it lands again. This is quite different from the green sandpiper which tends to almost make a vertical escape, flying up at a sharp angle before zig zagging down again. When you see a wood sandpiper flying you tend to notice its long legs dangling behind its tail.

The purple sandpiper is much darker than the other sandpipers, which tend to be mainly black and white. In some lights it almost seems to be black and if you are close enough you may see its yellow legs. To secure a more reliable field identification of sandpipers it is always worth noting the colour of their rump and any wing markings or bars on their tail. An especially white rump could indicate the rare curlew sandpiper.

Good places to look for a range of migrants this month are marshes, mudflats, lakes, reservoirs and especially along the estuary and sewage works. In many ways the latter habitat is similar to the inland freshwater marshes where these birds would have traditionally stopped off before so many were drained. East Tilbury and Rainham marshes are usually reliable places to see a good range of gulls, waders and terns.