Taxonomy of the populations of Sericornis beccarii inhabiting Cape York Peninsula

Abstract

There are two distinct forms of the Little Scrub Wren Sericornis beccarii inhabiting Cape York Peninsula: S. b. minimus, known only from the northern tip, with well-defined facial pattern, white-tipped wing-coverts and yellowish underparts. and S. b. dubius (= capensis) from the Rocky Scrub district, with much less clearly defined facial pattern, buffy or dull white-tipped wing-coverts and cinnamon-tinged underparts. Morphologically intermediate specimens are known from geographically intermediate localities. Sexual dimorphism is discussed; it is slight in S. b. minimus, but apparently present to a marked degree in S. b. dubius. A tentative reconstruction of the evolutionary history of the two forms is outlined; it is concluded that dubius has diverged farther than the other races of S. beccarii from the ancestral stock by losing its clear-cut facial pattern. Gene-flow at present between minimus and dubius is considered unlikely in view of the now fragmentary distribution of the rain-forest in the intervening area.