124 BIRDS OF THE COMMANDER ISLANDS. 



26 (31). Sterna paradisaea Brukk. 85. 



A few pairs breed regularly- in the northern part of Bering Island. 



27 (;}2). Stercorarius parasiticus (Lixx.) 8t5. 



Rather common in summer, breeding on the tundra. The light phase 

 is comparatively rare. 



In 1884 I received from Capt. E. I. Hunter, in Petropaulski, a speci- 

 men of the light phase (Nat. Mus., No. 101672), the bill of which is in a 

 condition that makes it highly probable that the basal covering, often 

 called the "nasal shield" or "cere," is shed periodically in the same 

 manner as in the Puffins {Fratercula and Lunda), {cf. Stand. Nat. Hist., 

 IV, Birds, 1885, p. 75). Unfortunately no date is given, but judging 

 from the condition of the plumage the bird seems to be in autumnal 

 dress. In birds which have the "cere" or "nasal cuirass" in per- 

 fect condition it covers the entire basal portion of the bill above the 

 nostrils and behind the "nail." Comparing the bill of a Stercorarius 

 with that of the Tufted Puffin [Lunda cirrhata), (Orn. Expl. Kamtsch., 

 pi. i and ii), it will be seen that the "nail" of the former corresponds 

 exactly with the red portion of the Puffin's bill, and the "cere" to the 

 deciduous green portion of the latter, only that in the Jasger the basal 

 part of the bill is proportionally more elongated than in the Puffin. On 

 both sides of the broad and somewhat iiatteued culmen the "cere" is 

 marked with a well-defined groove, which runs from the frontal feath- 

 ering to the "nail" parallel with the culmen, dividing the "cere" into 

 three longitudinal pieces, two lateral ones and one median. The lower 

 edge of the cere partly overhangs the nostrils, as will be observed if 

 one looks through the nostrils towards the light. This normal condi- 

 tion is represented in our figure, pi. vii, fig. 1, U. S. Nat. Mus., No. 75206. 



The other figure, pi. vii, fig. 2, U. S. Nat. Mus. No. 101672, represents 

 the specimen which is thought to be shedding the "nasal cuirass." {ef. 

 Stejneger, Orn. Expl. Kamtsch., p. 49, footnote.) Comparing it with 

 the normal bill it will be seen that the median piece, corresponding to 

 the "horny casque" of the Tufted Puffin, is raised somewhat from the 

 "matrix;" the lateral piece has separated entirely from the " subnasal" 

 portion, and on the side not shown in the figure the groove separating 

 the lateral and the median piece has also burst open for almost its whole 

 length ; the basal part behind the dotted line, in the figure, is dark, 

 adhering to the underlying part of the bill, while the anterior part has 

 a dull, yellowish, dead color, showing that it has loosened from the layer 

 underneath; the front border of the "cuirass" has broken off irregu- 

 larly ; the covering of the lower mandible is also in the progress of scal- 

 ing off irregularly. In short, the bill presents exactly the same aspect 

 as that of numerous specimens of Lunda in the act of shedding the green- 

 colored parts, and I entertain no doubt that the process of shedding is 

 as regular in the Stercorarii as in the Puffins. If that be the case, the 

 "nasal cuirass" would probably be soft and membranous in winter, be- 

 come hardened toward the breeding season, remaining thus until the 



