118 THE FLIGHT OF BIRDS 
of Africa. We were at the time just south of the 
Adriatic ; rain came Of about ten in the morning, 
and numbers of birds, finding themselves enveloped 
in cloud and unable to see their way, descended to 
the clear air near the surface of the sea and so became 
visible. Throughout the day there were continually 
fresh arrivals. Many accompanied the ship for 
miles, flying round and round her, and in some 
cases settling and resting ; otherwise they remained 
continuously on the wing. When the passengers 
had retired to their berths the Herons were still 
describing circles round the ship. Next morning 
they were gone, and the officers who had been on 
duty on the bridge reported that ten of the number 
had flown round and round till the sun rose and then 
had gone off northward, having probably sighted 
the west end of Crete. In all they must have been 
at least 16 or 17 hours on the wing. 
Migrant birds seem to have altogether exceptional 
power of endurance. Mr. J. L. Bonhote has called 
attention to the remarkable fact that when starting 
for a long voyage they are exceedingly fat, whereas 
they are thin when they reach their destination.* 
They would seem to live on their own fat, as the 
tadpole, when he is becoming a frog, lives by absorb- 
ing the fat in his tail. This is a very interesting fact 
which helps us to see how the thing is possible. But, 
in spite of actual or possible discoveries, the lasting 
power of migrant birds must always excite our 
wonder. Supposing that one of them takes no more 
than 130 strokes per minute—a very slow stroke— 
then, if he is on the wing 12 hours, the flight muscles 
* See Ornis, Feb. 1909. 
