Migrations of North American Birds. 293 



The present is not the occasion to discuss the nature of that 

 impulse which causes the bird or the fish to retrace its steps in 

 spring so unerringly ; the fact is a well-established one and of 

 much importance in reference to the multiplication or diminu- 

 tion of species. A region deprived of its spring birds or fishes 

 by extermination will only be filled up again in the course of a 

 long period of time. The result, however, can be greatly accele- 

 rated by artificial propagation in the places to be supplied. 



It may be considered as established that the migrations of 

 birds are generally more or less in a north and south direction, 

 influenced very materially by river-courses, mountain-chains, 

 forests, conditions of moisture, mean temperature, altitude, &c. 

 Middendorfif ('Die Isepiptesen Russlands^) suggests that birds 

 migrate in the direction of the magnetic pole, — a suggestion not 

 at all borne out by the facts in North America. 



It may be further remarked that, while birds proceed generally 

 in the spring to the very spot of birth, and by a definite route, 

 their return in autumn is not necessarily in the same line. 

 Many birds are familiar visitors in abundance, in certain locali- 

 ties, in either spring or autumn, and are not known there in the 

 other season. This is a fact well known to the diligent collector; 

 and I have been inclined to think that, in very many instances, 

 birds proceed northward along the valley of the Mississippi, to 

 return along the coast of the Atlantic. 



In general the northward, vernal movement is performed 

 much more rapidly, and with fewer stops by the way, than the 

 autumnal. 



Birds generally make their appearance in given localities with 

 wonderful regularity in the spring, the Si/lvicolidce especially, a 

 difierence of a few days in successive years attracting the notice 

 of the careful observer ; this diflference is generally influenced 

 by the season. The time of autumnal return is, perhaps, less 

 definite. 



[The foregomg is the paper spoken of by us on a former occasion (Ibis, 

 18GG, p. 416), and of which an extract in the 'Annals and Magazine of Natu- 

 ral History ' for last year is the only portion that has appeared in England. 

 Our contemporary the ' Jom-ual fiir Ornithologie ' has very properly thought 

 the entire paper worthy of translation ; and we now present it to our readers 

 in full coutidence that they will appreciate its high value. — Ed.] 



