Hybridisation between closely-related species is an ongoing threat to many species that can be exacerbated by anthropogenic practices. The Pacific Black Duck (Anas superciliosa) is a dabbling duck native to the southwest Pacific that is currently under threat of hybridisation with introduced Mallard (A. platyrhynchos). Mallard are known to hybridise with and threaten many other dabbling duck species throughout the world. To evaluate the threat posed by hybridisation with introduced domestic Mallards to the Australian subspecies of the Pacific Black Duck (A. s. rogersi), a set of nine microsatellite markers were selected to genetically differentiate these species and detect hybrids. The use of these microsatellite markers on putative Pacific Black Ducks found that the overall frequency of hybridisation in Australia is currently low (1.5%) and also revealed that the frequency of hybridisation tended to be higher in urban compared to rural Victoria. Behavioural observations suggested that while Mallards are dominant over Pacific Black Ducks, the latter have not been excluded from parks inhabited by Mallards. In contrast to mainland Australia, most birds on Lord Howe Island appear to be Mallards of New Zealand stock descent. It’s unclear whether hybrids resident were bred locally or whether they emigrated from New Zealand. The lack of Pacific Black Duck phenotypes on Lord Howe Island suggests that this species has been outcompeted by Mallards. In addition to hybridisation with Mallards, anecdotal reports have suggested that Pacific Black Ducks are also hybridising with Chestnut Teals (A. castanea). Based on microsatellite analysis, Chestnut Teal - Pacific Black Duck hybrids were detected, albeit at a low frequency (0.5%), among a sample of putative Pacific Black Ducks sampled throughout Australia
Overall, Mallard – Pacific Black Duck hybridisation does not currently seem to be widespread. However, the precautionary principle would advise eradication methods to be put into place to prevent the spread of the Mallard genome throughout Australia’s Pacific Black Duck population to protect the genetic integrity of the Australian subspecies.