Between 1803 and 1806 Le Vaillant also published in just the same style two volumes with the title of Histoire naturelle des oiseaux de Paradis et des rolliers, suivie de celle des toucans et des barbus, an assemblage of forms, which, miscellaneous as it is,.was surpassed in incongruity by a fourth work on the same scale, the Histoire naturelle des promerops et des guepiers, des couroucous et des touracos, for herein are found jays, waxwings, the cock-of-the-rock (Rupicola), and what not besides.
The first volume contains the " Colibris, Oiseaux-mouches, Jacamars et Promerops," the second the " Grimpereaux " and " Oiseaux de Paradis " - associations which set all the laws of systematic method at defiance.
To these he also adds the genus Promerops, 3 composed of 2 species of South African birds, of very different appearance, whose affinity to the rest can as yet hardly be taken as proved.
Layard, the habits of the Cape Promerops, its mode of nidification, and the character of its eggs are very unlike those of the ordinary Nectariniidae.