270 AI.EXANDER, Australian Sea Birds. K^aSu 



watching these birds, and have been interested therefore in ob- 

 serving their habits. Their flight is less rapid and more gull- 

 Hke than that of other Terns, though when they observe some- 

 thing in the water which attracts their attention they hover for 

 a moment to observe it, and then dive towards the water in the 

 regular Tern manner. I have never yet, however, seen them 

 actually plunge into the water, but just before they reach the 

 surface they check their fall and swoop over the surface, pick- 

 ing up the desired object therefrom with the bill like a (nill. It 

 is possible that this observation may not be of general applica- 

 tion, but due to local circumstances. The Brisbane River is so 

 muddy that objects are not visible at any distance beneath the 

 surface, and it may be that in clearer water they would dive for 

 food like their congeners. 



In writing about the White-tailed Black Tern (Chlidonias 

 leiicoptera) in The Bmu, vol. xvii., p. 95, I suggested that it was 

 possible that in this species the supposed winter i)lumage was 

 worn by the bird throughout its second year. I now make the 

 same suggestion as to the Gull-billed Tern. All through the win- 

 ter, specimens in three distinct plumages could be observed : 

 (1) A few birds with heads white more or less spotted with 

 black. (2) Numerous birds with the crown white, but a stripe 

 of black along each side of the head from the bill through the 

 eye. (3) Numerous birds with the crown and sides of the head 

 entirely black. 



I have seen all three of these plumages also during the sum- 

 mer, but have not seen enough of the birds to come to any defi- 

 nite conclusions as to whether their proportions arc the same. 



I suggest that birds in plumage (1) are first-season birds, (2) 

 birds in their second season, and (3>) adults. And the evidence 

 points to the j)robability that once the adult ])lumage has been 

 accjuired it is not lost again during the winter in Australia, what- 

 ever may be the case in the northern hemisphere. 



It is noteworthy in this connection that whilst many ducks of 

 the northern hemisjjhere, both in Europe and North America, 

 only wear bright plumage for a brief season in the early sum- 

 mer, and pass the rest of the year in the so-called "eclipse" 

 plumage, no similar seasonal change occurs among Australian 

 Ducks, nor as far as I can learn among the Ducks of South 

 America and South Africa. 



The Great Crested Grebe (Podiccps cristatns) in Europe 

 only wears its ruff during the siunmer, but, according to 

 Mathews, in Australia and New Zealand this ornament appears 

 to be worn throughout the year. I suggest that the GuH-billed 

 Tern once having acquired the black crown never loses it, and 

 that the birds supposed to be in winter plumage are really second- 

 year birds which have not yet acquired their black crown. 



Catharacta skua. Great vSkua. — T rnn using this name to cover 

 all the birds of this genus, as Hartert considers the southern 

 forms only subspecifically distinct from the Great Skua of the 



