176 



BRITISH BIRDS. 



[vol. xih. 



that is an unfortunate hiatus already explained, followed by 

 a period of rough weather in November in the western area 

 in which not a single migrant was seen. It is possible that, 

 as suggested for the spring migration, so the southward 

 migration is over sooner in the western area than in the 

 eastern. Perhaps rough weather alone cannot be made 

 responsible for the gap, because migrants were met with in 

 far rougher weather in April 1917. 



Figs. 6 and 7 are charts of the autumn migration of 191 7. 

 Fig. 6 represents the western area, a narrow strip of sea 

 from Malta to Cape Bon, and up the west coast of Sardinia 

 to Marseilles. Fig. 7 represents the eastern area, bounded 

 by a line from Malta to Port Said, from Port Said round the 



Fig 6. 



Fig 7. 



AUTUMN MIGRATION I917. 

 Fig. 6. WESTERN AREA. Fig. 7 EASTERN AREA. 



east and north of Crete back to Malta. The gap in the 

 middle of November is not due to rough weather : it is curious 

 that as in the spring migration of the same year the main 

 tide of migrants is followed by a gap, and then another small 

 stream. 



The division of the Mediterranean in this article into western 

 and eastern areas is not entirely arbitrary, because there seem 

 to be at least three main routes of migration apart from the 

 Gibraltar line. There is certainly one from Cape Bon to 

 Sardinia, Corsica and the Riviera, and another from Egypt 

 to Crete and Greece ; while very probably there is another 

 from Africa to Malta. Sicily and Italy. (The Mediterranean 

 west of a longitude seventy-five miles east of Minorca is 

 beyond the scope of this article.) 



