The Rufous Vanga Schetba rufa is endemic to Madagascar and lives in one-female groups. During the 1994-1999 breeding seasons, a total of 294 nestlings were banded. Among these nestlings, 51 stayed within the study area as spotted-throat individuals. In the next breeding seasons, 35 of 45 spotted-throat individuals were subsequently observed as black-throated males, and once they became black-throated males, these individuals never reverted to the previous spotted-throat pattern. In contrast, 30 banded nestlings were recovered as yearling females with white throats, and the female's color pattern never changed thereafter. All the spotted-throat males were helpers or floaters. All the males of one group consisting of an adult male with a black throat and two males with spotted throats were captured and sacrificed humanely. The testes were dissected from each specimen and were histologically examined. The testes of the spotted-throat males contained only spermatogonia, and no spermatids or spermatozoa were present. In contrast, the testes of the black-throated male were well-developed and contained enlarged seminiferous tubules with lumen, where numerous spermatozoa were evident. Considering these facts, spotted-throat males of this species are assumed to be sterile. We suggest that, due to their underdeveloped testes, the spotted-throat males (one-year-old males) of the Rufous Vanga are physically incapable of breeding. © 2002, The Ornithological Society of Japan. All rights reserved.