302 FIELD-STUDIES OF RARER BIRDS 



turf I mean which has been enlarged or at any 

 rate inhabited by rats, which, by the way, are often 

 most destructive to this species' eggs. 



In the majority of cases there is no attempt at 

 a nest, the eggs merely being deposited on what- 

 ever debris that may chance to exist at the bottom 

 of the selected hole or embrasure, such as and 

 customarily chips of rock or the crumbling soil, 

 but a slight hollow in the case of a soil-covered 

 chamber is often caused by the weight of the 

 brooding bird. On several distinct occasions, how- 

 ever, I have known small fragments of rock or stone 

 and a few shells brought in as a paving for the 

 ' bury " and as a reception for the tough-shelled 

 eggs, while on a certain small island off the Irish 

 sea-board I once found two clutches laid respect- 

 ively on a bed of withered grass and heather, though 

 I feel positive that these materials had originally 

 been conveyed into the holes by some other creature 

 and that probably a Shag or else had been 

 drifted into them. That the Black Guillemots 

 brought them there I cannot credit. 



Whilst it is true that the normal clutch of eggs 

 is two, one only is sometimes laid. This latter 

 trait was very marked in a small colony breeding on 

 the cliffs of the mainland and on those of some small, 

 adjacent islets off the north-west coast of Mayo, 

 whereas, barely seven miles off, on a mid-ocean 

 island, their fellows were all good for two eggs. 

 Possibly the food supply at the different fishing- 



