548 On Migration. 



they are a source of perpetual irritation and annoyance, to a 

 degree scarcely to be conceived by those who have not ex- 

 perienced it ; but to the birds which resort in such numbers to 

 those sequestered breeding-places, what an inexhaustible store of 

 the food best suited to their tender brood ! In a very much less 

 degree indeed numerically, but perhaps, in proportion to the 

 birds which breed in this inland district, not so far behind, are 

 the insects which spring forth into life with the warm days of 

 early summer, and which afford an ample supply of the food 

 they need, not only to the soft-billed Warblers which fill our 

 coppices and gardens in spring, but to the hard-billed Finches 

 and others, whose tender young equally require an insect diet 

 during the days of their dependence on their parents, while they 

 are yet confined to the nest. The profusion or scarcity of food, 

 then, is, I believe, the chief motive which regulates the migration 

 of birds, which also leads them to abound at one time in, and to 

 absent themselves altogether at another from, their favourite 

 haunts. But I do not say it is the only motive. The Warblers, 

 which come to us in the spring, would doubtless be led to seek 

 their breeding quarters in a temperate climate, more suitable to 

 their nature than the hotter latitudes wherein they passed the 

 winter. Those species, too, which leave us in the spring for the 

 far North, are doubtless attracted in some measure by the solitude 

 of the districts they frequent, where they can breed undisturbed 

 by the presence of man. But when the short Arctic summer is 

 ended, and the frosts of early winter paralyse the insect hordes, 

 then the parent birds lead their now full-fledged young to a more 

 genial climate in the South ; while our less hardy Warblers in 

 like manner move off with their broods to warmer latitudes. It 

 is very wonderful, indeed, if we reflect upon it, how such diminu- 

 tive creatures, so short- winged, so light, and so feeble, as some 

 are (the Golden-crested Regulus for instance), can prolong their 

 flight, as we know they do, over the Northern Sea ; or how others, 

 equally unfitted, as we should suppose, for so long a journey (the 

 Willow Warblers for example), pass on every autumn to the 

 interior of Africa, to return again to Wiltshire the following 



