1 88 SEA-BIRDS 



Quite hard earth and sandy rock is, by degrees, excavated with these 

 feeble tools. 



Information has now been gathered to give a fairly comprehensive 

 picture of the incubation and fledging periods of the tubenoses. 

 Coition takes place at or near the nest. Only one egg* is laid, and if 

 this is taken, even when fresh, another is not laid that year; except in 

 the case of some of the large albatrosses which, although normally 

 laying only one egg in two years, nevertheless lay a second egg in the 

 same year if the first be taken fresh (Matthews, 1929). Deliberate 

 nest building, except by the large albatrosses, is usually absent or at 

 most fortuitous or haphazard. Manx shearwaters will carry feathers, 

 dead bracken stalks, bluebell bulbs, roots, grass, etc., from near the 

 burrow entrance or from the burrow walls and this accumulates in 

 the form of a ring of debris around the egg or chick in the nest chamber. 

 The chick, too, may pull material in towards the nest from the burrow 

 walls. Fulmars and North Atlantic great shearwaters will pick up 

 and arrange small stones around the egg. In the Berlengas and on 

 Great Salvage Island Lockley found the North Atlantic shearwater 

 had built quite substantial platforms of small stones, and he surprised 

 one adult entering its cave with a stone in its bill. 



Incubation is by both sexes, though possibly the female sits 

 altogether rather more than half the period. Several observers of 

 burrow-nesting species have recorded that, in the first week after 

 laying, the egg may be left unattended by day, but we are inclined 

 to believe that this absence is often the result of fright due to the 

 handling of the adult when its ring number is being checked. Once 

 it is frightened in this way the adult may not return for more than 

 twenty-four hours, but this can be now explained by the fact that 

 petrels share the incubation period by taking shifts, generally of two 

 or, three, but sometimes of four and up to ten days at a time; and that 

 of some if not all species the off-duty bird does not usually return 

 each night until the end of its "legitimate holiday" is at hand. This 

 incubation by long shifts of several days has been conclusively proved 

 in the case of the North Atlantic great, the Manx and the little shear- 

 waters, storm-petrel, Wilson's, Leach's and Bulwer's petrels, the 

 frigate-petrel, and the fulmar. There is no evidence that the incoming 

 bird feeds the fasting bird, or that the male ever feeds the female 

 or vice versa at any stage (we except the oil-feeding of courting ful- 

 mars) ; and every indication that once incubation has begun the adults 

 * A very small percentage of fulmars (probably about one per cent) lay two eggs. 



