49 
Heligoland at a rushing speed during bright, warm afternoons in 
-early summer are observed to reach the oyster bed, 22,000 feet tu 
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 
‘shown 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 or~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 896 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 ta 
~ 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 
dime and direction of their movements, act with a means to an 
