76 
Proceedings of Royal Society of EdinhiLrgh. [sess. 
The Tactics adopted by certain Birds when Flying in 
the Wind. By Mr R. W. Western. (With a Plate.) 
(Read January 18, 1892.) 
All who watch the flight of hawks or kites are struck by the 
extraordinary power they have of sustaining themselves for a long 
time, sailing about in the air without flapping their wings or making 
any conspicuous effort whatever. 
Most birds of prey, as distinguished from game, are able to do 
this, and thus hold commanding heights from which to descry food. 
The expression “ wind-sucker,” as used by Ben Jonson, refers to the 
kestrel, a kind of hawk unsuited for falconry ; the astonishing way 
in which it keeps itself poised in the air, facing the wind with beak 
outstretched, led to the name, which implies the only explanation 
of the phenomenon that the science of those days could furnish. 
Sea-birds are also very proficient. 
The author’s own observations were upon Clieel^ a kind of kite, 
which after the parrot and crow, is the commonest bird in India 
(and excluding the pariah-dog, perhaps the most useful scavenger). 
The author once saw one of these get off a bough, wheel about in 
the air for two and a half minutes by the clock, and finally end up 
on the self-same bough, without having made a single flap of its 
wings during the whole time. 
Phenomena of this kind are quite beyond the reach of any 
parachute theory which assumes that the birds present so large an 
expansion of wing area in proportion to their weight, that the 
falling which necessarily takes place may be sufficiently small to 
escape detection. It will, however, be advisable to find an expres- 
sion for the amount of this falling, so as to determine it precisely. 
We must make the conventional assumption about the relation 
of the velocity of air to the pressure produced by it on a fiat 
surface, viz., that a fiat surface destroys the motion of all the air 
that blows against it in a direction at right angles. Of course, the 
relation is the same whether the air blows against the surface, or 
the surface is carried through the air, as in the present instance. 
