MIGRATION OF BIRDS. 153 



until he discovered that they required grasshoppers, 

 is a sufficient instance of the manifest necessity there 

 is for a peculiar food in one period of the life of birds ; 

 and renders it probable that, to obtain a certain 

 aliment, this willow wren, and others of the insect 

 and fruit-feeding birds, direct their flight to distant 

 regions, and is the principal cause of their migra- 

 tions. 



It is some stimulus like this which urges that 

 little creature, the golden-crested wren (motacilla 

 regulus), that usually only flits from tree to tree, 

 and never attempts upon common occasions a longer 

 flight, to traverse the vast distance from the Ork- 

 neys to the Shetland Isles over stormy seas that 

 admit no possible rest during its long passage of 

 above fifty miles L There it breeds its young ; but, 

 this one object accomplished, it leaves those isles, 

 dares again this tedious flight, and seeks a milder 

 clime. With us it never migrates, lives much in 

 our fir groves during the winter, and breeds in our 

 shrubberies in summer. Peculiar necessities, such 

 as these, may incite the migration of many birds ; 

 but that certain species, which lead solitary lives, 

 or associate only in very small parties, should at 

 stated periods congregate from all parts to one 

 spot, and there hold council on a removal, in which 

 the very sexes occasionally separate, is one of the 

 most extraordinary procedures that we meet with 

 among animals. 



If the sober, domestic attachments of the hedge 

 sparrow please us, we are not less charmed with 



