The intrinsic muscles of the syrinx fixed to the ends of the bronchial semi-rings ; both mandibles finely and evenly serrated on the terminal third of their edges; tongue tubular; bill long and cylindrical; the nestling resembling the adult female ; one moult in the year; wing of ten primaries, the first small; rectrices twelve; tarsus scutellated ; rictal bristles short.
The Nectariniidae, or Sun-birds, constitute a family of birds which are found only in the Old World and chiefly within the tropics. The Sun-birds are of small and delicate make and the majority are clothed in resplendent plumage. They are found solitary or in pairs ; they are entirely arboreal in their habits and they feed on minute insects and on the nectar of flowers. This latter they secure with their tongues when clinging to flower-stems, as they are unable to poise themselves in the air, after the manner of Humming-birds, except on rare occasions, and only then for a very brief interval. The males have a short but pretty song in the breeding-season. The Sun-birds build elaborate pensile nests at the end of branches or attach them to the underside of a broad leaf, such as that of a plantain (Musa). They usually lay two eggs, which are always, so far as is known, spotted.
After examining all the known species of Sun-birds I find that without exception they are characterized by having both mandibles of the bill serrated on the terminal third of their length. This character suffices to separate them from all the other Passeres except the Dicaeidae, and from these they may be distinguished by the shape of their bill, which is long, fine, and cylindrical, whereas in the Dicaeidae it is short and triangular. Under these circumstances the key to the families of Passeres (vol. i, pp. 8, 9) is susceptible of being considerably improved and simplified by deleting section a4, Tongue non-tubular and b4, Tongue tubular. The Nectariniidae may then be entered under section b1 together with the Dicaeidae, thus :—
b1. Both mandibles finely and evenly serrated on the terminal third of their edges.
c2. Bill long, fine, and cylindrical; primaries invariably ten…………………Nectariniidae.
d2. Bill short and triangular; primaries either nine or ten…………………Dicaeidae.
I find also that, for reasons explained in their proper place, the genus Chalcoparia cannot be placed among the Nectariniidae. The position of this genus is undoubtedly among the Liotrichinae in the family Crateropodidae, probably near Myzornis.
It has frequently been asserted that the males of many species of Indian Sun-birds have a distinct summer and winter plumage. After examining the very large series of Sun-birds in the British Museum, I am convinced that this is never the case. Full-plumaged males of all the common species, and it is of these that the assertion has been made, shot in every month of the year, or at such frequent intervals as to practically amount to the same thing, are in the National Collection, and prove that the adult males never change their colours. Young males are to be found throughout their first year in immature plumage, and these have probably given rise to the belief that a seasonal change takes place in the adult.
The young birds of both sexes resemble the adult female up to the first autumn moult. The males then commence to assume the colours of the adult and the change is effected very slowly and probably extends over a whole year.
The Indian Sun-birds may be conveniently divided into two subfamilies.
Sexes different; plumage of male in part metallic ; bill slender; nest pensile. Nectariniinae, p. 345. Sexes alike; plumage non-metallic; bill large ; nest cup-shaped, attached by a portion of the rim to a broad leaf…………………Arachnotherinae, p. 368.