1896.] Extensive Migration in Birds. 463 



evinced. Thus the postulate of Darwin, that wide-ranging- 

 species vary most, must be modified after a consideration of 

 the facts given here. But to pass over to certain apparent ex- 

 ceptions to the rule. Falco columbarius, breeding chiefly north 

 of the United States, and migrating in winter as far as South 

 America, has a variety (mcldeyi) on the Pacific coast from 

 Sitka to California ; Hdminthophila rnjicapilla, breeding as far 

 north as Hudson's Bay, and migrating in winter as far as 

 Guatemala, has a variety (gutturalis) from the Rocky Mts. to 

 the Pacific coast, in winter to Mexico ; and a number of simi- 

 lar cases could be mentioned, where the species, although it 

 has a wide range of migration, and a breeding area which is 

 not extraordinarily extensive, has, nevertheless, the tendency 

 to geographical variation. But such apparent exceptions to 

 the rule are, in fact, not valid objections, since in these cases 

 the geographical variety is much more restricted in the range 

 of its migration than the type species, or vice versa. And in 

 any of these cases, the species, including the variety, is to be 

 regarded as a number of individuals, some of which undertake 

 extensive migrations, while others migrate not at all or 

 through much shorter distances. Therefore, these are not 

 true exceptions to the law, that the extent of the migration 

 stands in inverse ratio to the amount of the tendency to pro- 

 duce geographical varieties; since a number of the individuals 

 do not undertake extensive migrations. Real exceptions may, 

 however, be found in such cases where the individuals of the 

 type species as well as its varieties make prolonged periodic 



migrations 



and after a careful examination of all the North 



species and their varieties, I have found only four 

 species which represent such exceptions to the rule : I)< ndroico 

 teatica, with its variety worcom!!. S> iuru* norehoraremi*, with the 

 subspecies nutabilis, S>f!ra,iia pimlln, with the variety pih-ohta, 

 and Tardus ustulatus, with its eastern variety suvinsomi. These 

 four species represent cases where, with not very extensive 

 breeding area, both races of the species possess extensive migra- 

 tion ranges. But I think that the importance of these cases as 

 exceptions to the rule is diminished, when we consider that in 

 each case the migration route of the variety is different from 



