The Black-vented Shearwater 



On Natividad Island, some 200 miles further south and close inshore, 

 a much larger colony was encountered ; and this, by reason of the friable 

 nature of the soil, permitted closer study. The breeding season was at 

 its height on the 10th of April, when each burrow contained either a pair of 

 Shearwaters and no egg, or else one bird sitting on the single egg. 



The distinction is a noteworthy one, and I dwell upon it (chiefly upon 

 my own responsibility) because Shearwaters, in common with most other 

 Petrels — and, indeed to some extent with the unrelated Alcidce — enjoy an 

 extended honeymoon during the period preceding the arrival of the egg. 

 The early phases of courtship take place upon the ocean ; but after the all 

 important decision is made (for that year at least), the happy couple go 

 ashore and renovate the old tunnel, or else sink a new shaft. The bur- 

 row, though not more than a foot and a half below the surface of the 

 ground, proceeds with many a twist and turn to a length of ten feet, 

 or less if the soil is stubborn. The nuptial chamber may or may not 

 boast a slight carpet of twigs or green leaves. 



Work on this tunnel has been carried on intermittently at night. 

 When it is completed the husband remains with the bride and expectant 

 mother for at least a month, faring forth with her only at night in quest of 

 food. In some species, as for instance, P. cuneatus, a week's absence from 

 the burrow on the part of both parents immediately precedes the deposi- 

 tion of the egg; but the prevalence of this habit is not clear, or at least 

 not certainly made out in the case of P. opisthomelas . 



After the arrival of the egg the male absents himself by day thence- 

 forth, returning well after dark, either to feed his mate or else to change 

 places with her for the night. [Careful records on this point are woefully 

 lacking in the case of most Tubinares.] It is this arrival and interchange, 

 varying endlessly according to the length of the daily wandering, which 

 occasions the nightly uproar. 



When the chick is hatched and during the days of tender infancy, 

 one parent remains with it constantly. A little later one parent mounts 

 guard by day, while both hunt at night. Later the gargantuan appetite 

 of the youngster requires the ministering service of both parents day and 

 night, while the chick's abundant down enables him to weather the 

 rigors of his subterranean cellar quite alone. 



Mr. Anthony sets the average date of fresh eggs for this species 

 as early March, 1 but the birds are often seen in abundance in more north- 

 ern waters at this season, or even much later. Nesting is, therefore, 

 either very irregular as to date, or else varies with the different 

 colonies. Each nesting island is a law to itself, and each season imposes 

 its own restraints. Of course there is a marked accession of numbers 



l Auk, Vol. XVII., July. 1900, p. 252. 

 2000 



