Page:Bird Life Throughout the Year (Salter, 1913).djvu/117

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with milder evenings, abundance of moths are flying at dusk. Of course mistakes are made, for how shall either bird or man forecast the vagaries of the English climate? The Swallows had appeared as usual in April, 1908, when the 24th of the month brought a snow-fall of nearly three inches. They vanished completely, and only returned when conditions once more approached the normal. The list of our British birds is swollen by the inclusion of a large number of species of purely accidental occurrence. Some of these waifs and strays have apparently, when migrating, got completely at sea as to direction, though no doubt in other cases they have been carried out of their course by contrary winds or sudden storms. The migrants usually travel by night, and perilous must be the passage in the gusty darkness of early April, till they see the fiery eye of Beachy Head or St. Catharine's flash-light leap out of the sea, and alight in the chilly dawn on English shores, to seek shelter in the nearest thickets at the back of the dunes. Perhaps the perils of the passage may account for the fact that the numbers of some species, as of the Chiffchaff and Lesser Whitethroat, vary greatly from year to year.

In distributing themselves over the country, the migrants follow well-defined routes. Their main arteries are usually the river-valleys, such as that of the Severn, and almost all have an objection to travers-