Variation in the Striated Heron Butorides striatus in Australasia

Abstract

Some populations of Butorides striatus are dimorphic. Rufous birds, which predominate over grey only in coastal mid-western Australia, appear to be morphs in which phaeomelanin replaces eumelanin in greater than usual concentrations. In normally pigmented (grey) forms there is geographical variation in depth of colour and in size. Apart from the usual trend for northern populations to be smaller than those farther south, variation is irregular and of the chequerboard pattern: populations in eastern Australia and the Solomon Islands are large and dark, those from western New Guinea to the Moluccas small and dark and those in north-western Australia, south-eastern New Guinea and the Meervlakte of northern New Guinea small and pale; populations of the second and third group intergrade in the Trans-Fly of southern New Guinea. Thus, it is difficult to trace geographical relations and routes of dispersal in the region; the patchwork variation in colour is thought to have resulted from random fixation in small founding populations.

The following subspecies are accepted: stagnatilis in coastal mid- and north-western Australia east to the Gulf of Carpentaria; macrorhynchus in coastal eastern Australia north to Cape York Peninsula; flyensis in coastal south-eastern New Guinea; moluccarum in western New Guinea and adjacent islands west to the Moluccas; idenburgi in the Meervlakte of north-western New Guinea: and solomonensis in the Solomon Islands and New Ireland.