MORTALITY AMONG BIRD MIGRANTS. 301 



As Mr. Dixon points out, the death-rate of a large 

 town standing at 50 or 60 per 1000, creates something 

 like a panic among its human inhabitants (the 

 average death-rate of London for the whole year 

 for instance is only 19.7 per 1000 *); but Mr. Dixon 

 thinks " there can be no doubt whatever that the 

 death-rate among birds, during migration, reaches 500 

 or 600 per 1000, and during exceptional circumstances 

 very much more," and "few there be that survive 

 it." f Indeed of the innumerable legions of birds 

 which leave their nesting grounds in the Arctic Zone, 

 and fly towards the south at the approach of winter, 

 but a small percentage survives to revisit them the 

 following year. " Only a fragment of these bird 

 swarms (Mr. Dixon thinks), countless, one was going 

 to say, as the sands on the shore, returns in spring." 



The perils of migration, according to the same 

 authority, may be divided into three important classes. 

 Fatigue, natural enemies, and blunders and fatalities 

 by the way; of which probably the first is the most 

 fatal ; but for further details on this subject we must 

 refer the reader to Mr. Dixon's monograph. 



We have gone into details with reference to the 

 migration of birds in this section, because we think 

 that it is in the Arctic Zone that peculiar 

 opportunities exist for investigating this subject, and 

 because it is these high latitudes that are the objective 

 of the longest flights performed by migratory birds; 

 in accordance with the law now almost universally 

 recognised among ornithologists, that " as a general 



* Returns issued by the Registrar General for the year ending Sep- 

 tember 26, 1892. 



t See The Migrations of Birds, by Charles Dixon, 1892, pp. 168, 169. 

 Ibid.^ p. 159. 



