Taxonomic revision, occurrence, and identification of Intermediate Egret Ardea intermedia in North Queensland, Australia

Adrian Walsh, Chris J. Chafer


Abstract

Between May and July 2021, five individual white egrets observed in Cairns, Queensland, Australia, appeared to have the physical characteristics of the nominate Intermediate Egret Ardea intermedia in non-breeding plumage, based on the mensurate bill methodology established by Cake et al. (2016). We review the taxonomic status of the Intermediate Egret complex, including A. intermedia (breeding in Asia), A. plumifera (breeding in Australia) and A. brachyrhyncha (breeding in Africa), using the species ranking criteria of Tobias et al. (2010). We subsequently performed an expanded comparative image-based morphometric analysis of the bills of 110 A. intermedia and A. plumifera from Asian and Australasian locations, including scaled digital photographic comparisons, and several multivariate and univariate analyses, as a test of taxon identification. In addition, we used Donegan’s (2018) universal effect size to determine if the taxa could be separated using only cranial–bill morphometry. The study showed a statistically significant dissimilarity in bill morphometry between the geographic populations, with five of the 55 Australian individuals being similar to A. intermedia. These analyses support our initial suspicion that the five birds at Cairns were A. intermedia, becoming the first recorded occurrence of A. intermedia in North Queensland or the eastern coast of Australia.

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