356 ]\IEXTAL EVOLUTIOX IX ANIMALS. 



a late period* to cross in its migrations the Eocky ]\Ionn- 

 tains ; and those " great highways, continuous for a hundred 

 miles, always several inches, sometimes several feet in 

 depth," worn by migrating buffaloes on the eastern plains, 

 are never found westward of the Eocky Mountains. In the 

 United States, swallows and other birds have largely ex- 

 tended, within quite a late period, the range of their migra- 

 tions.t 



The migratory instinct in Birds is occasionally lost ; as 

 in the case of the Woodcock, some of which have totally, 

 without any assignable cause, taken to breed and become 

 stationary in Scotland.J In Madeira the first arrival of the 

 Woodcock is known,§ and it is not there migratory ; nor is 

 our common Swift, though belonging to a group of birds 

 almost emblematical of migration. A Brent Goose, which 

 had been wounded, lived for nineteen years in confinement ; 

 and for about the first twelve years, every spring at the 

 migratory period it became uneasy, and would, like other 

 confined individuals of the species, wander as far northwards 

 as possible ; but after this period " it ceased to exhibit any 

 particular feeling at this season."|| So that we have seen 

 the migratory impulse at last worn out. 



In the migration of animals, the instinct which impels 

 them to proceed in a certain direction ought. I think, to be 

 distinguished from the unknown means by which they can 

 tell one direction from another, and l^y which, after starting, 

 they are enabled to keep their course in a dark night over 

 the open sea ; and likewise from the means — whether some 

 instinctive association with changing temperature, or with 

 want of food, &c. — which leads them to start at the proper 

 period. In this, and other cases, the several parts of the 



* Col. Fremont, Report of JExploring Expedition, 1845, p. 144, 



t See Dr. Bachman's excellent memoir on lliis subject in Sillimcni's 

 PMlosojph. Joxirn., vol. 30, p. 81. 



X Mr. W. Thompson lias given an excellent and full account of this 

 whole subject (see l^at. Hist, of Ireland, " Birds," vol. ii, pp. 247-57), "where 

 he discusses the cause. There seems reason to believe (p. 254) that the 

 migratorv and non-migratorv individuals can be distinguished. For Scotland 

 see St. John's Wild Sports ^of the Illr/hlands, 1846, p. 220. 



§ Dr. Heineken in Zoological Journal, vol. v, p. 75. See also Mr. E. V. 

 Harcourt's Sketch of Madeira, 1851, p. 120. 



II W. Thompson, lac. cit., vol. iii, p. 63. In Dr. Bachman's paper just 

 referred to cases of Canada geese in confinement periodically trying to escape 

 northward are ffiven. 



