xliv INTRODUCTION. 



or graze the surface of the deep. If the Wren, the Creeper, 

 and the Titmouse rest for an instant on a tree to snatch a hasty 

 morsel, in the next they are on the wing, to fulfil their destina- 

 tion. However abundant may be the nourishment which 

 presents itself to supply their wants, in general, birds of passage 

 rarely remain more than two days together in a place. 



The cries of many birds, while engaged in their aerial voy- 

 age, are such as are only heard on this important occasion, and 

 appear necessary for the direction of those which fly in assem- 

 bled ranks. 



During these migrations it has been observed that birds 

 fly ordinarily in the higher regions of the air, except when 

 fogs force them to seek a lower elevation. This habit is 

 particularly prevalent with Wild Geese, Storks, Cranes, and 

 Herons, which often pass at such a height as to be scarcely 

 distinguishable. 



We shall not here enter into any detailed description of the 

 manner in which each species conducts its migration, but 

 shall content ourselves with citing the single remarkable exam- 

 ple of the motions of the Cranes. Of all migrating birds, these 

 appear to be endowed with the greatest share of foresight. 

 They never undertake the journey alone ; throughout a circle 

 of several miles they appear to communicate the intention 

 of commencing their route. Several days previous to their 

 departure they call upon each other by a peculiar cry, as if 

 giving warning to assemble at a central point ; the favorable 

 moment being at length arrived, they betake themselves to 

 flight, and, in military style, fall into two lines, which, uniting 

 at the summit, form an extended angle with two equal sides. 

 At the central point of the phalanx, the chief takes his station, 

 to whom the whole troop, by their subordination, appear to 

 have pledged their obedience. The commander has not only 

 the painful task of breaking the path through the air, but he 

 has also the charge of watching for the common safety ; to 

 avoid the attacks of birds of prey ; to range the two lines in a 

 circle at the approach of a tempest, in order to resist with 

 more eifect the squalls which menace the dispersion of the 



