134 BULLETIN 121, UNITED STATES NATIONAL MUSEUM. 



I gave up looking for the entrances proper, and simply dug up the peat in any 

 spot that seemed likely to be free from roots. Unless violently disturbed, each 

 bird would be found sitting upon its egg, or perhaps it would back away a few 

 inches. 



Doctor Grinnell (1897) says: 



Most of the burrows each contained an egg, in Avhich case one bird, either 

 male or female, was sitting. In case there was a young one, neither parent 

 bird was present. When there were neither egg nor young in the hole, both 

 old birds were at home together. 



The southernmost colony that 1 have seen described is on the 

 Three Arch Eocks, off the coast of OrefTon, of Tvhich Mr. W. L. 

 Finley (1905) has written a very interesting; account. Here he 

 founcl this species breeding with Kaeding or Beal petrels, tufted 

 puffins, western gulls, Brandt, Baird, and Farallon cormorants, Cali- 

 fornia miirres, and pigeon guillemots. 



Eggs. — The single egg of the forked-tailed petrel is much like that 

 of the Leach petrel, but somewhat larger. The surface is smooth 

 but without gloss, and the color is dull white. There are usually 

 plenty of minute dark specks, purple or purplish black in color, 

 forming a cloud or a wreath about the larger end. Sometimes these 

 specks are quite large and conspicuous, but more often verj' faint or 

 indistinct. Some eggs show a few faint lilac spots. 



The measurements of 40 eggs, in various collections, average 33.9 

 by 25,7 millimeters; the largest eggs measure 37.5 by 28.5 and 35.4 

 by 27.5, and the smallest eggs measure 32 by 24.5 and 34 by 23.5 

 millimeters. 



Both sexes incubate, relieving each other at night and morning. 



Plumages. — The downy young when first hatched is covered with 

 long, soft, thick doAvn. foreshadowing the color of the parent. ex<^ept 

 on the chin and throat, Avhich are naked. The color varies from 

 " deep mouse gray " or " light mouse gray " above to " pale mouse 

 gray below." The young bird is nearly fully grown before the 

 plumage appears. Of the development of the plumage Mr. George 

 Willett (1912) writes: 



The first feathers to appear are those of the wings and tail, closely followed 

 by those on the back of the head and throat. Then comes the beautiful gray 

 covering of the back and upper tail-coverts, and shortly afterward the mature 

 feathers replace the down on the chest. The last down to disappear is that on 

 the lower abdomen. When this leaves the young is very similar in plumage to 

 the adult bird. The tail, however, is not so deeply forked, the white patch on 

 the throat is streaked with gray, the forehead is dark gray instead of brownish, 

 and the general coloration of the back, wings, and tail is darker than in the 

 adult. 



Food. — The food of the forked-tailed petrel consists of soft, oily 

 substances with perhaps a few minute particles of animal food 



