118 THE FLIGHT OF BIRDS 



of Africa. We were at the time just south of the 

 Adriatic ; rain came on 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. 



