Migra 



tion 



flight, but of migration in general we see very little, for the 

 reason that the birds as a rule fly at high altitudes, ranging 

 from 1 200 to 5000 feet. In autumn the migration is most 

 marked, for in spring the birds arrive in little parties, but 

 in autumn they travel in enormous flocks. Some fly in 

 pairs, some in sexes, the males arriving first and leaving 

 last. Sometimes the young birds migrate first. Some 

 travel only by day ; others, again, are night flyers. How- 

 ever they go, they always arrive and depart well to time. 



The direction of the wind appears to have little effect 

 on migration, but its force may render migration 

 impossible. They travel, for the most part, in the upper 

 layers of the air, for " birds are warmer blooded than our- 

 selves or other mammalia, and are capable of sustaining 

 life in rarefied atmospheres when these could not. By 

 a simple mechanical ascent, they can reach, within 

 a league or two, regions and conditions quite beyond 

 human knowledge ; where, selecting favouring air-strata, 

 they may be able to rest without exertion ; or find 

 meteorological or atmospheric forces that mitigate or 

 abolish the labours of ordinary flight, or possibly assist 

 their progress." 



The perils which envelop birds during migration are 

 enormous : the weaklings perish of fatigue and hunger ; 

 adverse winds drive them from land to sea. Predatory 

 birds, hawks and the like, accompany them, taking toll 

 en route, and predatory man awaits the tired wanderers 

 with gun and net. On foggy nights countless numbers 

 perish at the lighthouses, as the remarks of an observer at 

 the Skerryvore show, for he likens the birds around the 

 lighthouse to a heavy fall of snow. " Thousands were 

 flitting about ; hundreds were striking against the dome 

 and windows ; hundreds were sitting dazed and stupid on 

 the trimming paths ; and scores falling to the rocks below, 

 some instantaneously killed, others seriously injured, 

 falling helplessly into the sea. . . . Sometimes we use the 

 terms hundreds and thousands without thinking seriously 



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