The extreme pugnacity of humming-birds has been noticed by all observers, and it seems to be to some extent proportioned to the degree of colour and ornament in the species. Thus Mr. Salvin observes of Eugenes fulgens, that it is “a most pugnacious bird,” and that “hardly any species shows itself more brilliantly on the wing.” Again of Campylopterus hemileucurus,--“the pugnacity of this species is remarkable. It is very seldom that two males meet without an aërial battle,”--and “the large and showy tail of this humming-bird makes it one of the most conspicuous on the wing.” Again, the elegant frill-necked Lophornis ornatus “is very pugnacious, erecting its crest, throwing out its whiskers and attacking every humming-bird that may pass within its range of vision;” and of another species L. magnificus, it is said that “it is so bold that the sight of man creates no alarm.” The beautifully-coloured Thaumastura Cora “rarely permits any other humming-bird to remain in its neighbourhood, but wages a continual and terrible war upon them.” The magnificent bar-tail, Cometes sparganurus, one of the most imposing of all the humming-birds, is extremely fierce and pugnacious, “the males chasing each other through the air with surprising perseverance and acrimony.” These are all the species I find noticed as being especially pugnacious, and every one of them is exceptionally coloured or ornamented; while not one of the small, plain, and less ornamental species are so described, although many of them are common and well observed species. It is also to be noticed that the remarkable pugnacity of these birds is not confined to one season or even to birds of the same species, as is usual in sexual combats, but extends to any other species that may be encountered, while they are said even to attack birds of prey that approach too closely to their nests. It must be admitted that these facts agree well with the theory that colour and ornament are due to surplus vital energy and a long course of unchecked development. We have also direct evidence that the males are more active and energetic than the females. Mr. Gosse says that the whirring made by the male Polytmus humming-bird is shriller than that produced by the female; and he also informs us that the male flies higher and frequents mountains while the female keeps to the lowlands.