237 
1921.] Velocity of Migratory Flight among Birds. 
and 50 miles or so in distance seems nothing to these 
incomparable fliers. I have had splendid opportunities of 
observing botli the Alpine, Common, and Spine-tailed 
( Chcetura ) Swifts, and it has been a great disappointment 
to me that I have never been able to get a satisfactory 
estimate of their rate of flight, as they never continue 
on an even course. On a small island off the coast of 
Crete, I was recently given a good exhibition of what an 
Alpine Swift can do. I was watching some of these birds 
feeding round cliffs in which several pairs of Eleonora's 
Falcon were about to breed. Now, this delightful Falcon is no 
mean flier, and as these Swifts passed their cliff, the Falcons 
would come out against them like rockets. The Swifts 
would accelerate, and seemed to be out of sight before the 
Falcons were well on their way. So confident were the Swifts 
in their superior speed, that every time they circled round 
the island they never failed to draw 33 the Falcons, and 
seemed to be playing with them. I may add that these 
same Falcons have little difficulty in overhauling and striking 
a Rock-Pigeon—itself no mean performer. I have also 
seen on record the case of Falcons and Swifts somewhere 
in India, when the former failed time after time to come 
up with his quarry. I unfortunately cannot trace the 
reference. 
I hesitate to even guess at the speed to which a Swift can 
attain when the necessity arises, but the main point is that 
this, the fastest of birds, can increase his “feeding" speed 
of, say, 70 miles per hour to a velocity which must exceed 
100 miles per hour. There is little doubt that the speed of 
the Golden Plover in the table is an accelerated speed. 
Pilots in Mesopotamia have told me that whereas Geese 
cannot to any great extent accelerate, Duck, when pressed, 
could attain a speed of about 60 miles per hour % 
To conclude, I find that birds have two speeds-—a normal 
rate which is used for every-day purposes and also for 
migration, and an accelerated speed which is used for pro¬ 
tection or pursuit, and which in some cases nearly doubles 
the rate of their normal speed. Some of the heavier birds 
