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or deflected, Herr Gatke refers to the practical utility of keeping 

 records of the arrival and departure of birds in particular 

 localities, which he thinks are of very insignificant value. The 

 following remarks are curious but interesting. After noting the 

 impossibility of effectually watching a district of four miles in 

 diameter, he writes : — " The case of Heligoland is of course 

 different, for here we may say without hesitation that literally not 

 a single bird escapes observation." It will not be forgotten that 

 in another place he has expressed the conti'ary opinion, that the 

 number of rarities captured on the island is certainly exceeded 

 by those which have not been detected. He further adds — 

 " Notwithstanding, the results of notes of this nature can never 

 amount to anything more than a list of such disturbances and 

 interruptions of the main migration movement at the particular 

 place of observation. . . From this, however, we are not able 

 to form more than an approximate conclusion as to the actual 

 duration of the migration, since we can never determine whether 

 the first observed individuals of a species are in reality the 

 inaugurators of the migration at that particular time, or whether 

 they may not have been preceded weeks before by a vanguard 

 travelling, according to the normal manner of the migration flight, 

 at great and impenetrable heights above." Then follows the 

 following significant statement — " On the other hand, it would 

 appear to be extremely unsafe to base on observations of this 

 nature, the line of arrival or the migration front of a species, or 

 to draw conclusions from them as to the velocity of the migra- 

 tion flight. . . For in the first place, it cannot be determined 

 whether one is dealing with individuals whose spring migration 

 is proceeding in a northerly direction, and not with such as are 

 pursuing an easterly course ; and, further, one cannot establish 

 with any degree of certainty, whether the first observed indi- 

 viduals of a species are actually the breeding birds belonging to 

 the particular district of observation or not." 



The truth of Herr Gatke's contentions is self-evident, though 

 there are localities to which, in studying the migrations of par- 

 ticular species, they would not apply. As an instance, the colony 

 of Pied Flycatchers in the Lake District of England may be 

 pointed out. It certainly would not be very difficult to trace the 



