156 ANIMALS OF THE PAST 
population by accident in recent times and has” 
also retarded the arrival of man. 
Once established, flightlessness and size play 
into one another’s hands; the flightless bi 
has no limit placed on its size * while orentll 
a food supply and immunity from man; the 
larger the bird the less the necessity for wing ; 
to escape from four-footed foes. So long a 
the climate was favorable and man absent, the 
big, clumsy bird might thrive, but upon t 
coming of man, or in the face of any unfavor- 
able change of climate, he would be at a se- 
rious disadvantage and hence whenever either 
of these two factors has been brought to bear 
against them the feathered giants have van: 
ished. : 
‘2g 
REFERENCES 
There is a fine collection of mounted skeletons of va-— 
rious species of Moas in the Museum of Comparative 
Zoology at Cambridge, Mass., and another in the Amer | 
ican Museum of Natural History, New York. A fet : 
* While we do not know the limit of size to a flying creature, | 
none has as yet been found whose wings would spread over 
twenty feet from tip to tip, and it is evident that wings larger 
than this would demand great strength for their manipulation, — 
