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Heligoland at a rushing speed during bright, warm afternoons in 

 €arly summer are observed to reach the oyster bed, 22,000 feet to 

 the east, within the space of a single minute," i.e. a speed of 250 

 miles an hour. Gatke does not at all believe in the great fatigue 

 ishown by birds after migration, upon which Dixon dwells so 

 -graphically. Gatke says : — " After a night's incessant flight, a 

 greater or smaller portion of the succeeding day is all the birds 

 need for satisfying their hunger or recovering from such fatigue as 

 may have resulted from the exertions of their journey. I, myself, 

 that is Gatke, have never noticed cases of fatigue o* actual 

 exhaustion in regard to any birds which have landed here during 

 their migration, either by day or night, with the possible exception 

 of three solitary, but interesting instances, in which I observed 

 small land birds resting on the sea, half a mile from the island." 

 As to meteorological conditions, Gatke says, " It is a fact of 

 peculiar interest, that during both migration periods of the year, 

 all species, without exception, approach in largest numbers to the 

 earth's surface when very light south-easterly winds, accompanied 

 by clear, warm weather, happen to prevail for any length of time 

 in the lower regions of the atmosphere." The chief deterrent 

 influence of migration is fog. Dew and hoar frost are also 

 unfavourable to it. As to the order of migration, Gatke says : — 

 " That under normal conditions in the case of 396 species occurring 

 in Heligoland, with the exception of the cuckoo, the autumn 

 migration is initiated by the young birds from about six to eight 

 weeks after leaving their nests. That the parents of these young 

 individuals do not follow until one or two months later. That of 

 these old birds, again, the most handsome old males are the last to 

 set out on the migratory journey." This does not include a few 

 scattered examples of old birds, which have probably lost their 

 mates or their broods, which appear about a fortnight before the 

 young ones, but neither with them nor guiding them. At the end 

 of the first part of his book, Gatke writes : " Both in regard to 

 the immediate cause of the departure of birds on their migrations, 

 and in reference to what guides them, we are confronted with the 

 riddle which has hitherto defied every attempt at a solution, and 

 which indeed we may hardly expect will ever be likely to receive a 

 final explanation. Long and profound study has been devoted to 

 this subject in many quarters, and has resulted in the enunciation 

 of several very ingenious and plausible hypotheses. None of these, 

 ■however, will stand their ground, when the actual facts, which the 

 life of birds in Nature presents in such abundance, are marshalled 

 against them. In one way or another, however, almost every 

 attempt at an explanation admits that migrants, with regard to the 

 •time and direction of their movements, act with a means to an 



