V °g^n Recent Literature. 57 



cient cause, and perhaps it would be safest not to come to any decision on 

 this point." It is suggested that the more equatorial regions may be 

 "deficient in certain necessaries for the nursery," and also that these same 

 regions "would not supply sufficient food for both parents and offspring, 

 the latter being, at the lowest computation, twice as numerous as the 

 former, unless the numbers of both were diminished by the casualities of 

 travel." On the other hand, in view of "the pertinacity with which birds 

 return to their accustomed breeding-places," "the force of this passionate 

 fondness for the old home" must be taken into account, "even if we do 

 not allow that in it lies the whole stimulus to undertake the perilous 

 voyage." Beyond these few suggestions, it is rather surprising to find 

 little discussion of the 'causes' of migration. 1 



The manner of migration is considered at some length, illustrated by the 

 citation of a number of specific examples, and includes the discussion of 

 routes of migration, the literature of the subject being liberally cited, 

 either in the text or the accompanying foot-notes. The question — "How 

 do the birds find their way so unerringly from such immense distances?" 

 is considered to be "the most marvellous thing of all" and "by far the 

 most inexplicable part of the matter." "Sight alone," our author thinks, 

 "can hardly be regarded as affording much aid to birds — and there is 

 reason to think that there are several such — which at one stretch trans- 

 port themselves across the breadth of Europe, or even traverse more than a 

 thousand miles of open ocean, to say nothing of those — and of them 

 there are certainly many — which perform their migrations mainly by 

 night." The fact is apparently lost sight of that even at night — at least 

 in clear weather when birds mostly migrate — at the altitude at which 

 birds ordinarily perform their journeys, the main features of the land- 

 scape are distinctly visible for long distances to the migrating birds, and 

 that in reality "sight, and sight only, is the sense which directs these 

 birds," as truly as in the case of 'homing' Pigeons, where it is admitted by 

 "all the best authorities on that subject." In the case of birds travers- 

 ing wide expanses of open sea, sight is perhaps aided by other factors, as 

 notably the direction and temperature of the wind, combined with the 

 fact that even when such flights are quite extended they are of compara- 

 tively short duration, being performed by birds that for the most part 

 are exceptionally strong fliers, as many of the Grallas, etc. Prof. 

 Newton's idea that birds which perform their journeys by night cannot 

 possibly be aided by sight is almost demonstrably erroneous, as any one 

 who has spent a night on the summit of a high mountain and noted 

 the distinctness with which the landscape is spread out below him, 

 will readily believe. 



In regard to the subject of Mimicry, we must confess surprise at 

 finding so conservative and sensible a writer as Prof. Newton giving 

 such unreserved support to this theory as his article on the subject shows. 



1 On this subject cf. Allen, Auk, X, pp. 102-104, and Chapman, antea, pp. 12-17. 

 S 



