BIRDS OF N.W. WALES AND IRELAND. 181 



Storm-Petrel. — W. Occurs in small numbers on the west 

 coast during rough weather, generally in autumn. I. More 

 common in Ireland ; breeds in the west, but not in our two 

 counties. 



Black Guillemot. — W. Said to have bred on the Orme's 

 Head a century ago, but never does so now, and is indeed but a 

 rare straggler nowadays to North Wales. I. Breeds in small 

 numbers on the Dublin coast, less numerously in Wicklow. It 

 is more often met with in the north and west. 



It is impossible to read the foregoing without wondering what 

 can be the causes which have produced such wide discrepancies 

 in the faunas of two districts so near together, and so similar in 

 climatic conditions. In the case of a sedentary species such as 

 one of the Woodpeckers we can understand fifty miles of sea 

 acting as a barrier ; but if we take the case of a regular migrant 

 such as the Tree-Pipit, it seems passing strange that no in- 

 dividual of the species — so common on the one side of the 

 Channel — should ever find its way across the water to the 

 Emerald Isle. Here is, indeed, ample scope for study and 

 reflection. 



