REPORT ON THE MICiKATIOX OF BIRDS. 377 



iiidvidual cau ])ass over only one line of lui.uratiun, riie (|Uosti()n arises 

 whether flocks of individals. and even the whole species, can not in 

 the same manner foll(>^^' fixed rontes which snit tliem. Otlierwise, how 

 does it happen that ceitain species appear in numbers ever_\ Near in 

 fixed phices without showing- themselves in the neighborhood .' How 

 comes it that the single individuals at last find tlieir way back to their 

 old nesting places ? The climatological methods do not suffice to answer 

 these questions; others must be applied. 



As in any comi)licated problem, tlie order in which the different sides 

 of the question are taken up is not a matter of indifi'erence; for the 

 knowledge of some of its sides indisputably" heli)s to an understiinding- 

 ofcei'tain others. Which side of the phenomenon of nugration is to 

 form the scaffold f Which must be understood first, in a measure at 

 least, betbre the other (luestions can be pro])er]y asked, much less 

 answered. 



In fact, a ]irincii)al problem of the investigation falls within the 

 domain of zod-geography. for it must, first of all, be established irhich 

 roiiie the species takes before the time required to travei'se this route 

 and other circumstances connected with its passage can be considered. 



Sunderall pointed out emi>irically the course which the investigation 

 had to take when, in the year 1871, he made known the routes of migra- 

 tion of the ci'ane in Europe. 



With the conviction that only a systematically considered investiga- 

 tion could explain the migrations, the writer examined the (pn'stion 

 (Palmcn, i'lhcr /Ur Zu(/.strasscii dcr Vofjel, 187J:, 187<») with ])arti(nilar 

 regard to oidy a small number of hyperborean s])ecies. It seems neces- 

 sary to go into the (|uestion step by step, and first of all to fix the route 

 of those species of biids whose migrations seemed i)roper, to place in a 

 clear light the methods of investigation to be employed; for in this 

 relation it is not possible to com])arc all species of birds nor all the 

 regions penetrated with one another. 



In the choice of the zod-geographic, and therefore of the avilaunal 

 material to be em[)loyed. two different gToujJS of facts es])ecially pre- 

 sent themsehes. 



(1) Either the general migration of dilferent species would !ia\eto 

 be investigatetl, which is known to ha^•e awaketied theniost intense 

 interest of observers in many places; 



(:.') Oi" every individual s)»ecies is to be followed separately tlir(»ugh 

 all the regions which it \ isits in its migration. 



The enormons masses of nugratory birds which j)ass through certain 

 uarrow-bonnded regions long since attracted attention, for all descrip- 

 tions from those regions are highly i)ictures(pu' and eiitertaiidng. 

 Nevertheless, these rather touch onr sentiment than our i-eason. 'I'hey 

 leave the cpiestions whence; f whither? why? un-answeie<l, simply be- 

 cause each species can, proi)erly speaking, answer these <piestions only 

 in its own manner, but we ourselves can not separate and undei'stand 



