BIRDS small flocks of immature black-headed gulls, a few golden-plover, and occa- sionally a few redshanks, may still linger on. The only important bird of passage is the whimbrel, which in some years is very plentiful. Occasional knots and wood-sandpipers are also seen, and of late years a flight of black terns may linger in the west. The latest incoming birds at this season of the year are swallows, flocks of which have been recorded on the south coast, not only in the latter part of May, but as late as 9 June. These are probably on their way to nesting sites on the northern limit of their breeding area. Recent investigation has shown that land birds on migration avoid high- lying ground, adhere more or less closely to well-defined routes, often skirt the general shore-line for great distances, enter the land at regular openings on the coast, and when passing overland usually follow the direction of river valleys. The usual routes or flight lines of Cornish birds on migration appear to be somewhat complex. In the great autumnal invasion from the north-east many birds undoubtedly come into the county from Devon, but there is at the same time an important flight-line down the coast of the Bristol Channel. Systematic notes for the north coast, however, are still unfortunately somewhat scanty. The county lies too far away to participate in the great east-to-west rushes from the Continent that are so conspicuous a feature during the autumn months in the eastern counties, and consequently there is an absence of several east-coast casuals and vagrants, such as the blue-throated warbler, the barred-warbler, the icterine-warbler, Pallas's warbler and the great spotted cuckoo. Still it receives considerable accessions from birds that are migrating down the Channel both along the English and French coasts, and it seems probable that many of our casuals, as well as birds of a higher status from northern and central Europe, come to us, not across England, but along the western shores of the Continent. Both in the Channel and beyond it birds on autumn migration at times encounter heavy gales, particularly from the south-west, and are driven back on to the Isles of Scilly and the Cornish main- land, and especially into that great bay that stretches from Land's End to the Lizard. Most of the birds so driven on to our shores in the autumn are resident species, summer migrants and birds of passage in Cornwall, and cannot as a rule be distinguished from those belonging to the county, except when waifs and strays of an exceptional character are associated with them. It is probably due to the disturbance of coastal migration down the west of the European mainland by adverse weather, that we receive the fire- crest practically every autumn or winter. The occurrence of such vagrants at Scilly as the yellow-browed warbler, lesser-shrike, woodchat, ortolan- bunting, short-toed lark, little ringed-plover, tawny-pipit and red-breasted flycatcher, as well as of various unexpected accidental visitors on the south coast of the Cornish mainland as far east as St. Austell Bay is evidently due to the same cause. A remarkable feature among accidental visitors in the autumn and winter to the western half of the county is that no less than eighteen of the species are American. It is difficult to believe that these birds, with the possible exception of one or two individual cases of ' assisted passage,' could have come across the Atlantic. The usual explanation of the presence of such species in Western Europe is that the birds lose their way in the far north, and 315
