4 
NATURE NOTES. 
for any length of time ; and the account of the storing of air in 
air-sacs connected with the lungs is given, the volume of the 
bird being thus increased, while its specific weight is decreased. 
Humboldt, when travelling in the Andes, observed the height 
attained by a condor. Mr. Gatke calculated that from the 
distance at which it is possible to see a flag, the breadth of the 
condor’s wings, this bird must have reached a height of at least 
40,000 feet above the sea level. 
The velocity of the migration flights is even more wonderful, 
and, as the author remarks, with the arrival of the migratory 
period the whole bird nature is changed. They fly to unknown 
lands, the young ones going first, with no guide but instinct, at 
heights hitherto unattained, flying through the dark night at a 
speed undreamed of, and unequalled even by the great railway 
lines of England and Scotland. Sluggish flyers, such as hooded 
crows, reach a rate of 108 geographical miles an hour. The 
northern blue-throat, in fine weather, accomplishes a flight of 
1,600 geographical miles, viz., from Egypt to Heligoland in one 
spring night. Young birds of Richard’s pipit, in fine seasons, 
reach Heligoland early in September, about two months after 
leaving the shell ; the distance from Daiiria (their breeding place) 
to Heligoland is about 4,000 geographical miles. Another writer 
has suggested that their flight reaches 32 geographical miles 
a day; if so, they would not reach Heligoland until late in 
December instead of early in September. All these observations 
strengthen the conviction that birds have reserve forces brought 
into use for migration. Mr. Gatke gives conclusive evidence 
that the young take flight first, with no guidance from the older 
birds. The old male birds are the last to migrate, and the first 
to re-appear in early spring ; the author asks, “ What guides 
birds during their migration ? ” He suggests that the instinct is 
akin to that which leads a dog home by direct, unknown roads. 
He follows in imagination the flight of a young warbler from 
Norway, within the confines of the Arctic circle. Knowing the 
time is come, the young bird takes flight one evening at the time 
he would usually go to rest ; all landmarks vanish ; the little 
wanderer soars in the darkening sky till the blackness of night is 
round him, earth no longer visible, but on he speeds. At dawn 
he rests in Germany and feeds ; at evening he resumes his flight, 
crossing the Alps, and resting again by the Mediterranean ; 
again he starts at evening, nor rests again till he finds himself at 
his goal amongst the palm groves of Northern Africa. Yet more 
marvellous are the flights of birds from Southern Siberia. Mr. 
Gatke confesses his ignorance as to the causes of migration. 
Why should birds leave Northern Africa, where food is abundant 
and sunshine brightest ? 
The book of nature leaves many questions unanswered, even 
to lier most faithful students, and after his fifty years’ study of 
migration the author sums up the matter thus : — “ The life of 
man is too short for the complete exploration of this inexhaus- 
