06-Sept Wings Over London

For these reasons it is necessary to visit the favourite stopping-off points of various migrants several times during the month and preferably in the early morning. Being aware of the weather forecast both here and abroad may also help to predict what might be arriving or leaving and where the birds may be coming from or going to. Wind direction and the weather in other parts of Europe can radically affect what birds end up visiting us. Migrants, both common and rare, choose to stop off or take their migration route across London for a number of reasons. It may be they want to take advantage of good feeding areas so that they build up some weight for their ordeal ahead. Or the birds may stop, form larger flocks, and then wait for better weather conditions before continuing their journey. Migration in the autumn is usually taken far more leisurely than it is in the spring. The reason we might not notice some of the birds is that many may well be moving at night as well as travelling at high altitudes. Any unusual birds heard calling in the dead of night may be due to parties of redshank, meadow pipits or even skylarks passing over the city.

Fortunately we are able to see and enjoy the spectacle of this vast passage of birds in a number of ways. An obvious and favourite one is watching swallows and martins collecting on telegraph wires chattering excitedly prior to the next leg of their journey.

Hobbys are often drawn to such congregations looking for food and add to the excitement. Another is seeing a great rarity suddenly turn up. In London we are unlikely to see flocks descending from great heights in the early morning or other groups of birds flying together towards land from the open sea. We can, however, get a great feeling for what is happening around us when swallows are sometimes confronted by a headwind but still decide to move south. In such situations they often decide to fly much lower than usual, perhaps just above head height.

A Londoner sat in a park or garden may then witness the slow, steady wingbeat so typical of migrants as numerous swallows fly past one after another in exactly the same direction for possibly several hours. To see other spectacles you really need to be in the right place at the right time, so visiting favoured nesting areas such as reservoirs, marshes and mudflats is likely to increase your chances. Oddly it is the best time of year to visit Beddington sewage works, which is so popular with migrants. It may well give some clue as to what sort of habitat migrants chose before London was ever inhabited.

The scale of migration continues to gain momentum throughout the month and possibly thousands of birds are now moving through London and millions across the whole country. We may have had as many as fifty different summer visitors, most of which are now moving south bound for southern Europe or Africa. By the end of the month there will be very few still with us. Large visible waves of migrants tend to be more of a spectacle associated with October. If the weather has been unseasonally harsh further north in Britain or in Scandinavia we may even see our first winter visitors e.g. fieldfares, redwings, bramblings or perhaps even a snow bunting. A strong east wind may bring redshanks or siskins. Perversely against all the usual rules some herons may decide to fly north.

There are also many local movements or partial migrations. Resident birds, which may have chosen to raise a family in a remote safe habitat such as high moorland or upland pasture, now decide to relocate to an area where there will be richer food supplies for the months ahead. Coastal marshes along the Thames are always popular and here lapwing, redshank, snipe and golden plover may be seen. After leaving the nests, juveniles tend to wander at first, eventually teaming up with other birds of the same species and then finding themselves on a migration route. Birds to look out for include chiffchaff, willow warbler, whitethroat, spotted flycatcher, whinchat, wheatear, tree pipit and perhaps even, with immense luck, a turtle dove. With so many different migrants criss-crossing the city it is well worth examining any group of birds for rarities that may be in their midst.

Among any flocks of meadow pipits it is always worth checking for any rock, water or even a red-throated pipit. A lot of the birds seen are likely to be just the advance guard of a much greater wave that will be coming later. For this reason it is usually just small numbers which are recorded now in places such as Barnes Wetland Centre and various places along the estuary such as Crossness, Barking, Rainham and Tilbury.