54 



front, the neighbouring islands should be equally patronised. 

 Indeed, the position of Heligoland can hardly be called central, 

 except in relation to Western Europe, and with reference to a 

 migratory flight between the points of north and south. Another 

 point may be noticed with regard to the spring migration to 

 which Herr Gatke calls attention, viz. the much smaller number 

 of certain species which pass the island at this period of the 

 year. This he accounts for on the theory that birds travelling 

 from their winter quarters to their breeding grounds take the 

 most direct route possible at this period of the year. The 

 majority, therefore, traverse lines of flight passing much to the 

 east of the island, and generally speaking, in a south-westerly 

 to north-easterly direction. Ingenious as the theory may be, it 

 is quite unsupported by any positive evidence, and is in direct 

 conflict with the author's assertion, expressed on page 25, that, 

 observations conducted on the island have established the main 

 facts that in autumn the migration is from east to west, and in 

 spring from west to east. As an instance that all birds do not 

 return in spring by the most direct route to their breeding 

 grounds, the Shore-Lark may be pointed out. This species passes 

 Heligoland at this period in considerable numbers by an appa- 

 rently west-to-east route, though its breeding grounds lie far to 

 the north of the latitude of the island. 



To the writer, the great mortality which must of necessity 

 take place amongst birds, affords a much more probable explana- 

 tion of the fact of the smaller number of migrants being observed 

 in the spring. If we only reflect what the numerical increase of, 

 say, 100,000 pairs of birds would amount to in a few years, allow- 

 ing four young as the annual production of each pair, and the 

 young themselves breeding the following year, it is at once 

 evident that a single species would soon over-run the whole earth, 

 unless some check on its constant increase were not always in 

 action. 



The position of the island may here, perhaps, lend an 

 additional explanation of the fact of fewer birds being observed 

 in spring. In the autumn many species will be nearing their 

 winter quarters, and consequently travelling very slowly and 

 lingering in any locality likely to afford rest and refreshment ; 



