300 IJEPORT ON VHi: MIGIUTION OF ]!IRDS. 



"Tliis divergence toward llie iiortli (mor<' oi- lews eousiderable) de- 

 pends essentially upon the fact that each species has its particular 

 routes, the direction of which is modified according to the nature of 

 the localities which suit this species, and which it seeks also during its 

 migrations, at least for stopping places; and for this reason the migra- 

 tion routes even of a single species, starting from different parts of 

 the region which it inhabits in snmmer, are not parallel, but for many 

 species convergent towards the south, for many others divergent. 

 This iip])lies much more forcibly to the routes of a luimber of species 

 wliich, in the season of migration, concentrate in some locality i)ar- 

 ticularly almndant in birds of passage." 



The author therefore categorically maintains that the individual 

 species, according to their jjeculiarities, are dependent on the topo- 

 graphical relations of the territory through which they migrate, and 

 that the rontes of each species accordingly assnme a particular 

 geographical form. 



In the same spirit Prof. Menzbier also reports (1886, Bull. Soc. 

 Nat. Moscow) on the results of his investigations on the migration 

 routes of the birds in European Russia. He unconditionally joins 

 those inquirers who maintain that each si^ecies moves along peculiar, 

 strongly marked routes, because during the migration they are de- 

 pendent upon the condition of the country through which they happen 

 to be passing. He agrees in dividing the routes according to their 

 topographical character into categories, which, however, are compli- 

 cated by transitions. 



He also lays stress upon the fact (pp. 333, 351) that the relations of 

 the ground and the conditions of procuring food do not always suffice 

 to explain the situation of these routes ; but that the routes mark 

 fairly well the ways along which a species has once migrated, and 

 tliat about the same ways are still utilized as a result of inherited 

 tendency. (Compare on this sul)iect the writer's Zngstr., cap. x, as 

 also Weismann.) 



Menzbier furthermore refers (p. 354) To the importance of the spring 

 stragglers (comi>are Palm<''n, Ziif/str., ix, p, 238 -v^ .sr^/.), which under 

 favorable circumstances may remain in a region where they have ar- 

 rived by chance, and, nesting there, may chq^uge the bird fauna in a 

 characteristic manner, Finally the author discusses the order of 

 migration of the individuals, and appears to favor tbe belief that the>' 

 change their relative positions (Yoriiberzug). lu conclusion, he de- 

 clares that migration routes in the course of time, in consequence of 

 geological changes in the topography, may pass from the compass of 

 one group into that of another, 



To these results, which agree with those of the writer. Prof. Menzbier 

 adds corrections of some of my statements and conclusions, which are 

 worthy of acknowledgment. The conclusions reached in the years 

 ISli-lO respecting the migration routes were founded on tacts which 



