258 BRITISH SEA. BIRDS. 
egg. Both birds assist in making this burrow, 
which often runs under some mass of rocks, and 
many holes are begun and deserted for no apparent 
reason, just as we find to be the case with the 
Sand Martin and other hole-boring species. At the 
entrance of all of the holes that are occupied there 
is a considerable heap of droppings. Few, if any, 
Shearwaters are astir even at a populous breeding- 
station during the day; all keep closely to their 
burrows, remaining stolidly upon their nest until 
dragged forth, struggling, into the light. Many 
burrows are made close together, and in some cases 
one main entrance will lead to several chambers, 
each containing a nest. 
