MIGRATION. 279 



and gloomy forests that afford shelter during summer 

 to these fowls, which in winter disperse over the 

 greater part of Europe. In these arctic regions, in 

 consequence of the thickness of the woods, the ground 

 remains soft and penetrable to the woodcocks, and 

 other slender-billed fowls ; and for the web-footed 

 birds the water affords innumerable larvae of the gnat. 

 The days are there long, and the beautiful meteorous 

 nights indulge them with every opportunity of 

 collecting so minute a food ; whilst mankind is 

 very sparingly scattered over those vast northern 

 wastes. 



The migration of winter birds of passage doubtless 

 proceeds on the same general law as that which regu- 

 lates the movements of those birds which spend the 

 summer with us and leave us in winter. Birds which 

 find the temperature and circumstances of our sum- 

 mer most congenial to their wants and habits retire 

 on the approach of severe weather to find something 

 similar in the south ; while 'others which remain 

 among us in winter, to avoid the extreme rigour of 

 that season in the most northerly regions, return to 

 their own country when that rigour has abated. 

 Nevertheless, there are difficulties in accounting for 

 the migration of the winter birds of passage, which 

 are not so apparent in the case of the others. The 

 following are some of those difficulties, which we give 

 nearly as stated by Mr. Collinson, in vol. 44, for 

 1747, of the Philosophical Transactions. 



There appears no necessity, either on the score of 

 food or climate, for their departure from us. They 

 probably come here in winter for the sake of food 

 and a more genial climate than that which they have 

 left ; but in some very severe seasons, when there is 

 a great scarcity of berries, they find their subsistence 

 here with difficulty, and often perish from the want of 

 sufficient food. It is, therefore, unaccountable that 



