Variation and speciation in the genus Climacteris Temminck (Aves: Sittidae)

Abstract

The present paper determines the status and range of forms in the genus Climacteris Temminck (tree-creepers) formerly regarded as species; it also reviews infraspecific variation, re-defines races, and is a detailed study of speciation in the genus. Climacteris is a most interesting genus in the information it yields with respect to speciation, Forms occur that represent the full range of intermediate stages right up to the one that has demonstrated its specific distinctness by secondarily contacting the parental stock without interbreeding. The number of forms with the "potential" of developing into new species is unusually high, 0.8 per species in Australia, or 1.5 for Australia and New Guinea combined, The fundamental isolating barriers are tracts of arid country that cause extensive gaps in the habitats to which the various species are adapted. This presupposes an initial climatic deterioration which isolated remnant populations in "refuges", a theory that has already been introduced into ornithology by Gentilli (1949), Mayr (1950), and Serventy (1951). Climacteris differs from the related genus Neositta (nuthatches), studied by Mayr (1950), for in the latter a secondary climatic improvement has led to an increase in range and multiple hybridization. In Climacteris there is evidence of some secondary spread but, with one exception, distinctive geographically representative forms are still isolated.