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or less extent migratory, and it is shewn beyond doubt that apparently weak-winged 

 birds like Begtdus cristatus, Accentor modularis, the Paridae, Troglodytes parmdiis, 

 ErUhacus ridjecnla, Passer domesticus, and montanus, and even Certhia famiUaris are 

 equal to crossing the North Sea in its broadest parts in a single flight. 



As a rule, the young of the year appear to migrate some weeks in advance of 

 the old. Exceptions are Gucidus canoms and Caprimidgus europaeus. In these two, the 

 old birds migrate in the autumn some weeks before the young. 



In the spring the males often migrate in advance of the females. At this season 

 also birds travel, with rare exceptions, at night, and as the weather is finer, and 

 the nights shorter and clearer, do not fly low and run their heads so much againts 

 the lanterns of lighthouses. The spring migration is also carried on much more 

 leisurely, migrants proceeding by easy stages to their northern breeding quarters, 

 and there are none of those great „waves" and „rushes'" often continuous for days 

 and weeks, which are so characteristic of the autumn migration. In spring also, 

 migrants strike the lanterns from 1 1 p.m. to day-dawn — the majority after midnight, 

 and not in the early hours of the night, as is commonly the case in the autumn. 

 Migrants seem to follow narrow lines in spring, broad in autumn. 



The period of migration of each species extends over a considerable time. 

 Sometimes it is over in four or five weeks, in others going on for months, and even, 

 as in the case of Alauda arvensis^ for half-a-year. Indeed, migrants on passage are 

 crossing the North Sea in every month of the year, and no sooner does the ebb of 

 the autumn cease — and it is sometimes prolonged into February — when the flood 

 sets in, and birds ars passing northward once more. In each ease of normal migration, 

 a given species will continue on passage day by day or week by week, till the maxi- 

 mum is reached in „a great rush,'' the main body passing forward, after this there 

 is a falling off' in numbers till the migration of that species ceases or is completed. 



In 18S6, from notes supplied by Herr Gätke, the first visible and decided 

 passage of birds — Alauda arvensis and Sturmis vidgaris— across Heligoland from west 

 to east commenced February 15th; the movement becoming decidedly pronounced 

 on March 19th. and in gradually increasing numbers and species to May 25th, after 

 this, intermittent in small and scattered parties to the end of June. On the 27th 

 and 28th of June, there was the first perceptible movement of birds on the return 

 migration, eleven species being noted, all young ; this movement was continued 

 throughout July to August 1 8th, with a gradual increase in regard to quantity and 

 the species under observation. From August 19th to October 25th, a very strong migration 

 almost daily; after this, and to the end of the year, a gradual falling away, the 

 throbs and pulsations of the great rush becoming daily more feeble and less sustained. 



The period of the migratory flight in the autumn, of any species or genus, is 

 probal)ly referable to two causes: the first, one of temperature, affecting the time 

 of nesting; the second, more or less dependent on it. is the period at which the 

 young arrive at maturity, or rather that period when they cast off' parental control. 

 or are themselves thrown off by the parents. When able to procure food on their 

 own account they flock together and migrate in a body. Thus, we can readily 

 understand how the young of the raj^torial birds nesting about the s-ame date, over 

 a widely extended area in Northern Europe, would arrive at this self-dependent 

 stage together, when there would follow a simultaneous movement, ending in a 

 migrator]^ rush, giving rise to such phenomena, as the annual passage in the autumn 

 of Accipifer nisiis, in enormous numbers across Heligoland, as recorded by the eminent 

 ornithologist Herr Gätke, or the great flight of Pernis apivorus, from east to west. 

 some years since, on Sei^tember 19th, prolonged for six hours. This migration of 

 Pernis is the more remarkable from the fact that these birds are very solitary in 



