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134 NATURAL SELECTION > viother surrounding objects, before we can say that the bird,when sitting on its nest, is really conspicuous. It has beenremarked that small patches of white and black blend at ashort distance to form gray, one of the commonest tints ofnatural objects.5. Sunbirds (Nectariniidse). In these beautiful little birdsthe males only are adorned with brilliant colours, the femalesbeing quite plain, yet they build covered nests in all the casesin which the nidification is known. This is a negative ratherthan a positive exception to the rule, since there may be othercauses besides the need for protection which prevent thefemale acquiring the gay colours of her mate, and there is onecurious circumstance which tends to elucidate it. The maleof Leptocoma zeylanica is said to assist in incubation. It ispossible, therefore, that the group may originally have usedopen nests, and some change of conditions, leading the malebird to sit, may have been followed by the adoption of a domednest. This is, however, the most serious exception I have yetfound to the general rule.6.Superb warblers (Maluridse). The males of these littlebirds are adorned with the most gorgeous colours, while thefemales are very plain, yet they make domed nests. It is tobe observed, however, that the male plumageis nuptialmerely, and is retained for a very short time ;the rest ofthe year both sexes are plain alike. It is probable, therefore,that the domed nest is for the protection of thesedelicate little birds against the rain, and that there is someunknown cause which has led to the development of colourin the males only.There is one other case which at first sight looks like anexception, but which is far from being one in reality, anddeserves to be mentioned. In the beautiful waxwing (Bombycillagarrula) the sexes are very nearly alike, and theelegant red wax tips to the wing-feathers are nearly, andsometimes quite, as conspicuous in the female as in the male.Yet it builds an open nest, and a person looking at the birdwould say it ought, according to my theory, to cover its nest.But it is, in reality, as completely protected byits colorationas the most plainly coloured bird that flies. It breeds onlyin very high latitudes, and the nest, placed in fir-trees, is