312 Recent Literature. f hll'' 



nearly one hundred pages the author makes an important contribution to 

 the literature of the subject, through, especially, his record of observations 

 on the nocturnal movements of birds as observed by himself and others 

 through telescopes. This detailed record, with the accompanying dia- 

 grams, forms an 'Appendix' of some 50 pages. The main discussion is 

 divided into four chapters: (i) Historical Review; (2) The Causes of 

 Migration; (3) Migratory Routes ; (4) The Manner of Migration. The 

 first two chapters seem rather perfunctory and unsatisfactory; the second, 

 on the causes of migration, closes with the following statement of the 

 author's conclusions : "Birds are set in migratory motions by a complex 

 combination of changes in temperature, humidity and living nature. 

 The cause for migration, however, is the failure of food in two wide- 

 spread areas — the north and the south — at opposite seasons of the year " 

 (p. 196). He also says (p. 191): "It has been maintained for years that 

 the question of food will never explain the vernal migrations, howevei" 

 well it serves that purpose in autumn. . . . The assumption that the ques- 

 tion of food will not explain the vernal migration has proljably been due 

 to our ignorance of the physical conditions of the south." He then cites 

 a remark of Weismann's to the effect that "ponds, rivers and creeks 

 become dry, insects disappear and even vegetation fails in many regions 

 of the south in summer," and quotes "Mr. C. R. Ricker " (/c^'-*?, C. B. 

 Riker 1) on the effect of the dry season on vegetation, etc., at Santarem, 

 Brazil (Mr. Winkenwerder, however, does not state the locality of Mr. 

 Riker's observations), and adds: "Do not cases of this kind give us 

 rather striking evidence that the food supply of the south is limited ? " 

 To Mr. Winkenwerder the inatter is very simple. He says: "We have 

 thus two areas in the geographical distribution of birds that are deficient 

 in food at opposite seasons of the year, and we can see readily enough 

 the cause for migration, both in the spring and in the fall "! 



Under 'Migratory Routes' the author describes the methods and dis- 

 cusses the evidence afforded by the extensive series of observations on the 

 nocturnal movements of birds as seen through telescopes at Madison and 

 Beloit, Wise, Lake Forest, 111., and Detroit, Mich., during May, 1900, and 

 also in April, May, September and October, 1 898-1901, at Madison. The 

 theory of migratory routes is considered as established, and also the 

 theory that they are determined by the topographic features of the areas 

 traversed. 



Under the head of ' The Manner of Migration ' are considered ' Numbers 

 associated in Migration,' 'The Altitude attained in Migration,' and the 

 'Associations of Individuals and Species.' Nine thousand birds per 



' Mr. Riker's name is constantly misspelled "Ricker " throughout the paper, 

 Coues appears as "Cowes", other names of authors are also misspelled, and 

 Mr. Brewster's paper on bird migration is cited repeatedly as "Bull. Nutt. Orn. 

 Club, No. I," though sometimes correctly as Mem. Nutt. Orn. Club, No. i. 



