272 BRITISH HIRDS. [vol. xiv. 



out if it were only a rather useless relic of the ice-age. Indeed, 

 he practically defines migration as the journey that is under- 

 taken — whether it be a hundred yards or a thousand miles — 

 at the season when the gregarious instinct gives place to the 

 exclusive instinct, and vice versa. 



The book seems to me a convincing exposition of a theory 

 that in general, as the result of rather different observations, 

 I already held. There are, however, various considerations 

 that Mr. Howard seems to me to overlook, or on which he 

 lays insufficient emphasis. 



My first criticism is that he almost ignores the fact that 



many birds are known to return to the place where they 



were bred. He gives a belated recognition of the fact in the 



second part of his last chapter, but he does not seem to realize 



what an important bearing it has on his whole theory. A 



bird begins its life in a restricted territory ; the first journey 



it undertakes is the autumn journey, not the spring one ; 



the spring journey is, in very many cases at any rate, merely 



a return along the old tracks. So that the overpowering 



impulse to seek a territory in spring is not a completely' new 



instinct even in the first year ; it is essentially a " homing " 



instinct. And this, surely, accounts very largely for the 



varying numbers of species in a given district from year 



to year ; if a large proportion of the young survive their 



first winter the number will increase ; if old and young both 



perish there may be none, until some neighbouring district 



becomes too heavily populated. Of course, if a bird returns 



to its old home and cannot establish itself by reason of 



competition, it may have to wander to some new localit}^, 



and thus, as Mr. Howard shows, the breeding-range may 



increase. I have known a Reed- War bier appear on a marsh 



in the middle of June in the south of England ; and last year 



near Birmingham a Chiffchaff appeared in a locality in June 



and sang constantly every day for the next month or more ; 



but in neither of these cases, so far as I observed, did a mate 



appear, so that the attempt at fresh colonization was a failure. 



Again, it does not seem to me that Mr. Howard estimates 



the relationship of the female to the territory and to the male 



correctly. He admits near the end of the book that the 



recovery of marked birds shows that the female, as well as 



the male, is apt to return to its old home to breed. But 



earlier in the book he pictures the male arriving first and 



the females wandering round without any special inclination 



towards any special place, until they happen to encounter 



unmated males defending a territory. My own impression 



