Bower Building and Decoration by the Bowerbird Amblyornis inornatus

Abstract

Bowers of the little‐known bowerbird Amblyornis inornatus are the most elaborately decorated structures erected by an animal other than humans. I studied populations in two mountain ranges. South Kumawa bowers consisted of a tower of sticks glued together, up to 2.6 m high, resting on an almost perfectly circular mat of black moss. Decorations were black, brown, or grey: leaves, snail shells, acorns, sticks, stones, and elytrae. The mat, decorative sticks, and elytrae were painted shiny black, possibly with an oily material in excrement. Another group of bowers 8 km distant differed in also using colored fruits as decorations. Wandamen bowers differed drastically in the much lower stick tower, woven but not glued, covered with a stick hut up to 2 m in diameter, resting on an unpainted green moss mat, and decorated with colored fruits, flowers, fungi, butterfly wings, and leaves. Objects tended to be grouped by color, with certain types of objects at specific locations. Within either mountain range there was individual and age‐related variation among bowers. Many or most decorations were objects commonly available in the forest. Decorations turned over from day to day.Wandamen birds were tame. The diverse vocalizations included vocal mimicry. Males raided each others' bowers and chased off other bird species. Bowerbirds may modify their environment by dispersing fresh fruits used as decorations, dispersing seeds of fruit eaten, and caching fruit.Colors of objects used as decorations are not a passive sample of locally available objects, nor do they necessarily match the plumage of females or of rival males, nor are they necessarily rare or habitat‐specific. Instead, color preference and many other features of bower design appear to be arbitrary characteristics of species or populations. I suggest that bower style is partly learned, and that geographic variation in bower style may depend upon culturally transmitted behavior, analogous to geographic variation in bird song dialects.