15 



adverse agency, the attack might well cause the extinction of the 

 species. 



As to its reinforcement, or it may be re-establishment, it has been 

 suggested, and I think with good reason, that immigration plays an 

 important part ; but unless favourable circumstances prevailed at the 

 time, it could not go very far towards producing the vast abundance 

 that has at times been noted. 



I do not for one moment suggest that we know all that is to be 

 learned about this interesting species, and it appears to me that, now 

 that it is apparently again becoming common, it is a fitting time to call 

 attention to it, in the hope that those of our members who have the 

 opportunity may make a special study of it, with a view to finding 

 out what are the reasons for the great fluctuations in its numbers 

 that from time to time take place. 



