MIGRATION OF BIRDS. 183 



fill up vacancies, and leave nothing unoccupied. I 

 have repeatedly known districts, from which during 

 the winter season every blackbird, thrush, gold, 

 and bull finch had been killed, yet in the ensuing 

 spring observed their places filled by others, and the 

 song in the grove, and nesting in the brake, as har- 

 monious and as plentiful as usual. Many sports- 

 men know that killing down their game does not 

 universally prevent a supply in the ensuing season, 

 nor the saving of whole covies assure in that part of 

 the manor an unusual number of breeding pairs, 

 but like mankind they colonise, and send out parties 

 to inhabit unoccupied places : entirely domesticated, 

 and half reclaimed creatures may remain where they 

 were bred, but perfectly wild and free ones seem 

 generally to obey this mandate of nature. With 

 man, necessity, or some political cause usually in- 

 cites this separation, but with animals it appears 

 most often to be the mere fulfilment of an appointed 

 ordination : the intrusions of men and his habits 

 may drive timid creatures away from established 

 abodes to another which is free from his annoyances, 

 but the jealousy of some creatures, which incites them 

 to drive others from the vicinity of their stations, 

 and the bickerings and contentions of the elder birds 

 with their offspring, forcing them to form new set- 

 tlements, are only modes of accomplishing these 

 designs of nature. But this must be understood in 

 a limited sense, and not of universal, invariable 

 occurrence, for there are various groups of animals 

 and creatures dispersed over particular regions of 



