Letters, Extracts, and Notes. 709 



matliematically straight line, sustaining themselves with 

 practically synchronous vibrations of the wings. But here, 

 over the open sea, when the birds were flying straightaway 

 for considerable distances, a rythmical rise and fall was un- 

 mistakably apparent. The dip of the body, though less 

 noticeable than in the flight of many Passerine birds, was 

 nevertheless regular, and occurred, as nearly as I could 

 judge, at intervals of about one second.'^ 



The Peruvian Guano Islands. — Dr. H. O. Forbes, M.B.O.U., 

 the ornithologist appointed by the Peruvian Government to 

 investigate the question of the guano deposits in the islands 

 off" the coast of Peru, has lately returned to England. The 

 diminution in the quantity of guano had occasioned dis- 

 quietude to agriculturists and it was decided to ascertain, if 

 possible, the cause of the decline, which has been going on 

 for some time. It so happened, however, that just before 

 Dr. Forbes^s arrival in Peru, which was early in January, 

 1912, a very remarkable incident occurred. For some reason, 

 at present unaccounted for, in November, 1911, almost the 

 whole of the birds on certain islands forsook their nests and 

 newly-hatched young and did not return. Millions of 

 nests containing many millions of dead birds were thus 

 forsaken. Shocks of earthquake are not uncommon in these 

 islands, and the birds which live there are always greatly 

 alarmed when such disturbance occurs. They rise and wheel 

 about in much agitation, exhibiting every evidence of the 

 fear which the convulsions occasions in them. Dr. Forbes, 

 after rejecting other and unsatisfactory theories, surmises 

 that an exceptionally severe shock may have caused the birds 

 in this instance to take the extremely uncommon course of 

 forsaking their young. No one could say in what direction 

 the y migrated. His own belief is that they went north to the 

 Galapagos Islands, but he was unable to verify this 

 impression. The birds disappeared for three months and 

 although they began to return in February and March, 

 1913, they did not resume breeding at that time, and 

 SER. X. — VOL. I. 3 b 



