Great Invasion of Crossbills in 1909. 333 



In Italy articles and letters recording the extent and 

 progress of the Crossbill invasion in that country have been 

 published in the Journal ' Avicula,' in the ' Bulletin' of the 

 Italian Zoological Society, and in some local newspapers, and 

 further information, it is to be hoped, may still be forth- 

 coming, not only from that country, but also perhaps from 

 other parts of South Europe. 



Before giving the statistics which I have been able to 

 obtain regarding the occurrence of Crossbills in various parts 

 of the Continent, I wish to make a few remarks of a 

 general character concerning the subject in question, and 

 specially with reference to the following points connected 

 with it, viz. : the cause which has determined or brought 

 about this erratic migration or wandering of the species ; 

 the country or countries from which the birds have chiefly 

 come ; and, lastly, the influence or governing force, if there 

 be any, which has regulated the course, expansion, and 

 duration of the migration. 



Taking these points in the order above-mentioned, and 

 commencing with that of the cause of this unusual movement 

 on the part of a species not a true or regular migrant, the 

 reason which naturally first presents itself to one's mind is 

 that of a scarcity of food in the bird's habitual range ; and 

 this, I venture to think, is probably the right one. 



The Crossbill, as is generally known, is at times a veritable 

 vagrant or gipsy among birds, as it has somewhat appro- 

 priately been styled, its roving on such occasions being 

 apparently influenced by alack of sufficient nutriment in the 

 northern coniferous forests which are its chief home ; and 

 this failure in its natural food-supply has probably been 

 the cause of the species wandering in the present, as it has 

 doubtless been in previous, instances. 



The exceptionally severe weather that prevailed throughout 

 a considerable portion of the European Continent during the 

 previous winter and spring months probably interfered with 

 the development and ripening of the cones in the northern 

 pine and fir woods, and brought about this failure in the 

 bird's principal food. 



