Tuesday, May 22, 2018

The changing relative abundance of grey duck (Anas superciliosa) and mallard (A. platyrhynchos) in New Zealand

TitleThe changing relative abundance of grey duck (Anas superciliosa) and mallard (A. platyrhynchos) in New Zealand
Publication TypeJournal Article
Year of Publication2017
AuthorsWilliams, M
JournalNotornis
Volume64
Issue4
Pagination211-228
Type of ArticleFull article
KeywordsAnas platyrhynchos, Anas superciliosa, Anatidae, grey duck, hybridisation, mallard, New Zealand, status
Abstract

Change in the relative abundance of grey duck (Anas superciliosa) and mallard (A. platyrhynchos) in New Zealand, from 1950 to the present day, is summarised from trapping records, hunters’ kills, and field studies. Mallards achieved numerical ascendency over grey duck throughout most of New Zealand by the late 1970s, merely 20 years after the cessation of mallard releases by historic acclimatisation societies. Post-1990, the relative abundance of mallard in almost all districts, as recorded from hunters’ kills, appears to have stabilised at 90%, or higher. Uncertainty about hunters’ and the public’s ability to discriminate between grey ducks, their hybrids with mallard, and variably-plumaged mallard females is demonstrated and most modern (post-1990) records of relative species abundance must be regarded as quantitatively suspect. Ducks identified as grey ducks by hunters are now a relative rarity throughout New Zealand, except in Northland and West Coast. Post-1990 duck trapping in North Island indicates that grey ducks, where reported, are patchily rather than generally distributed. The absence of genetically-validated criteria for discriminating ducks of grey duck x mallard hybrid ancestry continues to confound field identifications of both species.

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