148 PROCEKDrXGS OF THE ACADEMY OF [1892. 



Other specimens are like the mature white-breasted birds but 

 still have the under wing coverts and axillaries barred. 



As none of the specimens above described were birds of the year 

 it is reasonable to suppose that it takes at least two years for the 

 species to acquire the full adult plumage. The great variety of 

 coloration exhibited by these Jaegers makes it difficult to arrange 

 them in any order which will show the steps in the transition from 

 young to old. It seems to me most probable that the normal 

 plumage of the bird of one year is shown by No. 26,907, while the 

 young "bird of the year" doubtless shows still more barring, per- 

 haps even on the breast. As this bird appi'oaches the adult stage 

 (i. e. No. 26,909) the barrings are gradually replaced by uniform 

 slate gray. 



The specimen No. 26,904 may, I think, represent a partial dusky 

 phase as the suftusion of sooty feathers on the under surface is very 

 decided, much more so than in any of the young birds, with which 

 I at first placed it. The dusky feathers moreover, do not form 

 transverse bands as in the young birds and the under wing coverts 

 are uniform slate colored like those of the adults. The under tail 

 coverts are, however, still barred with white. 



Iftiiis really represents a dusky phase, it seems to be the first 

 recorded instance of it in this species, though it occurs regularly in 

 the closely related iS. parasitmis. 



If, however, we consider this as a young bird it would indicate 

 that the adult plumage is assumed very differently by different 

 individuals, as there is another specimen which has not a trace of 

 dusky marks on the breast but which has the under wing coverts 

 strongly barred. 



The measurements of the specimens are as follows : 



Acad. Collec. 

 No. 2(5,905 female 



2ti,903 

 2(i,902 

 26,90-1 

 2(i,9(l6 

 2H.909 

 26,907 male 



8. Gavia alba (Gunn.) Ivory Gull. 



A series of eight males of this beautiful species was collected in 

 Melville Bay, July 6 to 17. Some of the specimens, probably 

 younger birds, have dusky tips to the primary coverts. 



