The Plumages of Nesonetta aucklandica Gray.
[Read before Canterbury Branch, Royal Society of N.Z., September 1, 1937; received by the Editor, December 15, 1937; issued separately, June, 1938.]
Existing descriptions and coloured figures of Nesonetta aucklandica Gray are alike defective in that they fail to define the distinctive plumage characters of male and female and to indicate the close correspondence of plumage pattern and moult sequence of this duck with those of Anas chlorotis Gray.
Gray's description of Nesonetta aucklandica (1845, 16) is too brief to have much comparative value and could not apply to an adult male in breeding plumage. The plate (1845, pl. 17), presum ably of the type, shows none of the gradations of brown on the sides and flanks nor the contrasty blackish under tail coverts of the adult breeding male. Buller's plate (1888, vol. II, pl. XLII) shows an immature bird or an adult female. His accompanying description (1888, p. 263) can also apply only to a female, or male in full eclipse plumage. In a later account, Buller (1905, p. 14) states that “the sexes do not differ much from each other, both exhibiting the delicate reflections on the plumage of the upper parts, but the male may be distinguished by its darker head and neck, by the black under tail coverts and by a greater abundance of vermiculated markings on the sides of the body.” As a female of this duck never shows any vermiculated feathers this remark seems to indicate that Buller was not familiar with the distinctive plumage of the sexes. The sexing of skins made by commercial collectors in New Zealand can seldom be relied on; an undoubted male skin in the Buller collection in the Canterbury Museum (No. 0.1219.5) bears a label in Buller's handwriting accepting it as a female. As Oliver (1930) describes the female as having “vermiculations on side of body less marked” the matter is no further advanced.
The adult male here described is taken to be in nuptial plumage. It is in the collection of the Canterbury Museum. (No. 0.1219.3), has no data attached except sex and locality. It has been mounted since 1910 and appears to be one of the birds collected by the late Edgar R. Waite at the Auckland Islands in June, 1912. Specimens labelled with date and indication of careful sexing seem almost impossible to find in the long series of specimens of this duck distributed in collections all over the world. A description of the male plumage follows:—
Head and neck sepia, dull on foreneck and very slightly mottled with pale buff on the chin, warmer in tone, admixed with black, and glossy on cheeks and crown; patches of glossy green commencing behind the eyes and spreading caudad on to the hind neck where they meet, ending level with the sepia area of the foreneck. The upper breast and sides of breast bright russet shading to tawny on lower breast and flanks, the feathers of this region being obscurely
marked with subterminal spots of dark sepia. The belly presents a mottled appearance, feathers being tawny with a large central spot (and sometimes bars) of sepia, and pale edges, and much more distinctly barred on thighs and under tail coverts. The general colour of back, wings and tail is dark sepia, but on mantle and scapulars, as on the flanks, are finely vermiculated feathers of sepia and whitish buff. In a few of these feathers on the thighs the whitish buff becomes pure white, forming sharp contrast with the black under tail coverts. When the wing is viewed from behind there is a definite speculum caused by the distinct oil-green gloss on the outer webs of most of the secondaries, which are edged with pale cinnamon and white. A gloss of the same green is noticeable on upper wing coverts, upper tail coverts, rump and some of the scapulars and mantle. Some of the outer scapulars have their outer webs edged with black. Tail coverts dark sepia edged with dark tawny. Primaries sepia, lighter on inner webs.
The following description of a female is taken from a bird collected at the same time as the male described above. The correctness of the sexing in this case is confirmed by its similarity to an adult female collected at Ewing Island, Port Ross, Auckland Islands, in March, 1923, by G. Archey; this bird was preserved in spirit and recently dissected by one of us (R. A. F.).
There are no vermiculations anywhere at any stage. The head is generally sepia, but without gloss except slightly purplish on the crown. The chin, throat and foreneck are more distinctly mottled with white than in the male. Breast and flank feathers Saccardo's umber at the base merging to tawny olive at the edges, without subterminal spots. By a transition well defined from the lower breast, the belly feathers are sepia broadly edged whitish. Under tail coverts sepia with indistinct lighter edges. Upper parts dark sepia with scapulars edged with tawny, the whole of the upper surface having a green gloss similar to that of the male but fainter; speculum less distinct, the outer webs of the secondaries having only the same amount of gloss as the rest of the upper surface.
The series of spirit specimens in the Canterbury Museum is further valuable as indicating that males undergo an eclipse plumage. Of six specimens collected at Port Ross in March, 1923, five are males. They lack the decorative features of the male plumage taken in June and early spring, and only here and there are odd vermiculated feathers to be found hidden in the rest of the plumage. Otherwise these birds have a general resemblance to females, but differ in their greater size, absence of distinct whitish throat patch, and by having more or less barred and mottled feathers on the belly where those of the female are plain sepia edged with dull white. Particulars and dimensions of this Ewing Island series (collected by G. Archey, March, 1923) are as follows. (Tail measurements are omitted owing to variable abrasion. The moult referred to is the body moult.)
It has not been sufficiently emphasised that in the nuptial male plumage there is no essential pattern difference between Nesonetta aucklandica and Anas chlorotis. Plumages are variable in the latter species, and the general tone is usually a shade lighter than in Nesonetta. The males of the two species show a closer resemblance than females and immature birds, but there is not sufficient material available in collections to decide on the exact degree of resemblance.