STARTING 57 
of proved fact. Even now, though the subject has 
been much studied, it would be very rash to venture 
on a formula. The big bird has great advantages. 
He can manage, as we have seen, with a relatively 
smaller expanse of wing, for the area, being greater 
absolutely, does not so readily allow the escape of 
air atthe margins. Moreover, his wing, being longer 
absolutely, is a more powerful lever. The great 
weights which Eagles, for example, carry show that 
there is no deficiency of lifting power. But the big 
bird’s wings have not the easiness of rotation at the 
shoulder-joint which makes it possible for a Green- 
finch, for instance, or a Pheasant, to rise with a steep 
incline ; he cannot put himself in the right attitude. 
It does not appear, however, that bulk in itself is 
any handicap. 
If this be so, it may well be asked why even big 
birds are quite small when compared with the larger 
mammals. I have already pointed out that the big 
bird, if his legs are short, has difficulty in beginning 
a flight, and so lacks a very important accomplish- 
ment. Then why are they not all mounted on stilts, 
like the Flamingo ? But legs of such length, or even 
the half of it, would for many birds be most incon- 
venient appendages, for a diving bird most of all. 
They would not help him to rise from the water, and 
they would be clumsy things beneath the surface. 
And thus among big birds there are many that for 
purposes of flight are handicapped by shortness 
of leg. Diminutive size brings with it another 
advantage. The small bird comes more rapidly to 
maturity. In his second spring, when he is not yet - 
twelve months old, the Blackbird has already paired 
