318 INTRODUCTION TO ZOOLOGY. 



their migration. It is now ascertained, that the greater 

 number of these summer birds leave these kingdoms for the 

 north and west of Africa,* whence they return annually, with 

 such punctuality, that their appearance is looked for with con- 

 fidence within a day or two of the particular time. 



These few simple facts are nearly all that we can he said 

 to know with certainty on the mysterious subject of migration. 

 It has been asserted that birds change their quarters because 

 of inclement seasons, scarcity of food, and other evils, which 

 are avoided by their change of residence. But if these sup- 

 posed explanations be scrutinised, they will be found unsatis- 

 factory. The truest philosophy is candidly to avow our ig- 

 norance of the subject, and to regard birds as acting under an 

 impulse implanted in their constitution by the Creator. Ob- 

 servation only corroborates, that " the Stork in the heavens 

 knoweth her appointed times, and the Turtle and the Crane 

 and the Swallow observe the time of their coming."! 



Several observers have stated, that migratory birds, when 

 in confinement, though plentifully supplied with food, show 

 evident symptoms of restlessness when the period arrives at 

 which their fellows take their departure. So powerful is this 

 migratory instinct, that birds will forsake their young and 

 leave them to perish, rather than not accompany their com- 

 panions. This proceeding, so contrary to all that we see of 

 the devoted attachment of the parent birds to their offspring, 

 was first observed by Mr. Blackwall, who states J that, in the 

 spring of 1821, a pair of House-martins, after taking posses- 

 sion of a nest which had been constructed in the preceding 

 summer, drew out the dried bodies of three nearly full-fledged 

 nestlings, which had perished in it. About the same time, 

 another pair of House-martins, being unable to dislodge the 

 young, closed up the aperture with clay. This suggested 



* Several British species were observed, on their migration northward, 

 by Mr. W. Thompson, when on his passage from Malta to the Morea, in 

 H.M.S. Beacon, in April, 1841. Annals Nat. Hist. vol. viii. p. 125. 

 f The lines of Pope are highly descriptive and appropriate: 

 " Who bid the Stork, Columbus-like, explore 

 Heavens not his own, and worlds unknown before ? 

 "Who calls the council, states the certain day, 

 Who forms the phalanx, and who points the way? 

 God in the nature of each being sounds 

 Its pr6per bliss, and sets the proper bounds." 

 J In his Researches in Zoology. 



