18/6.] Mil. H. SAUNDERS ON THE STERCORARIlN.E. 329 



whilst the offspring of two similar parents will "breed true." This 

 point can only be solved by some ornithologist who will devote his 

 attention to a colony during the breeding-season, observing the pro- 

 duce of all these unions, and, if possible, marking the nestlings before 

 they take wing ; perhaps some of our Scotch friends will take the 

 hint. 



That the sooty plumage is not merely a sign of immaturity is 

 shown by the long tail-feathers, and by the burnished tinge of the 

 acuminate ones on the nape. 



It is worthy of notice that in Spitzbergen, its most northern 

 breeding-ground, neither Dr. Malmgren nor Professor Newton found 

 a single example of the dark whole-coloured form ; all those which 

 Admiral Collinson's and Dr. Rae's Expeditions brought home from 

 the far north are also white-breasted specimens, which looks as if 

 the dark form was a more exclusively southern one. 



In the white-breasted birds the striations on the underparts 

 decrease with age until little more than a pectoral band remains ; 

 this, again, becomes narrower until in some specimens it entirely 

 disappears and the bird is white from the chin to the abdomen. 



This species has the most extended range of any member of the 

 family. Parry found it up to lat. 82° 2' N. ; and it breeds throughout 

 the arctic and subarctic regions, as far south as the islands of the 

 north of Scotland ; and Thompson records it as having nested near 

 Achil Island on the west of Ireland. I should not be surprised to 

 learn that there is some beeeding-place along the western shores of 

 France ; for both old and also very young birds occur at Malaga 

 early in August. Some go higher up the Mediterranean ; but others, 

 principally the young, continue their course along the west coast of 

 Africa, to Walwich Bay and as far as the Cape of Good Hope ; and 

 in those waters they pass the months of what is our winter, compel- 

 ling the Terns and the small Gull (Z. kartlaubii) to disgorge their 

 prey. From the altered appearance which they present in their 

 progressive stages of plumage at a time when European naturalists 

 have lost sight of them, an individual from the vicinity of St. Helena 

 received the name of 5. spinicaudn. Careful examination of a series 

 of specimens from the Cape of Good Hope, where Mr. E. L. Layard 

 only observed them from December to February, showed that all 

 were in the act of losing and renewing the central tail-feathers and 

 the outer primaries, which are the last to be moulted ; and although 

 at the first glance the birds have a somewhat distinct look, yet there 

 can be no doubt whatever of their being our northern species. 

 Most that I have seen are birds of less than a year old, although 

 this immaturity is less noticeable in the dark-plumaged birds than 

 in the lighter ones ; in none, however, are the central tail-feathers 

 fully developed, and most are still partially in the quill-sheath. One 

 specimen, evidently obtained just before the northward migration, is 

 absolutely the same as a bird of only two months older from the 

 Faroes. It is to be presumed that S. crepidatns goes up the east 

 coast of Africa, as Mr. Allan Hume obtained it (naming it iS. asia- 

 ticus), and observed many along the coast of Sindh, the Gulf of Oman, 

 and between Guadcr and Bombav. 



