SPREAD OF THE FULMAR. 89 



matter of interesting conjecture what causes have operated 

 to bring it about, for so far as we can judge, the usual 

 causes of extension of range of a species are absent in this 

 case. We are familiar with many instances in which 

 birds have increased notably within recent times, owing 

 to the extension of favouring conditions. The Missel 

 Thrush, for example, has greatly extended its range 

 within the present century in harmony with the increase 

 throughout the country of the plantations it loves to 

 frequent ; and similar instances might be given of wood- 

 land birds, such as the Blackcap, having followed the 

 planting of shrubberies into localities where they had pre- 

 viously been unknown. But in all such cases there has 

 been a change in the environment which the birds have 

 taken advantage of, and no such explanation is applicable 

 in the case of the Fulmar. 



The beetling cliffs of Shetland, which are now in process 

 of being colonised by these birds, are the same now as 

 they have been for ages, and can show no greater attrac- 

 tions at the present time than they presented centuries 

 ago. Nor does there seem any reason to suppose that any 

 difference in the food supply furnished by the Shetland 

 seas can enter into the case, for though the stranded 

 carcase of a dead whale is said to have attracted the first 

 birds to Foula, the influence of this is at least very pro- 

 blematical, nor would it account for the continued steady 

 spread of the birds. 



Has any change occurred in its stronghold at St. Kilda 

 to cause the bird to seek out fresh breeding haunts ? Of 

 this I can find no evidence. It is true indeed that the 

 population of St. Kilda has diminished notably since 

 Martin's day, when the islands supported 180 persons ; 

 but there has been no considerable change for many years 

 past, the population appearing to average some 70 to 80 



