The Mallard x Pacific Black Duck Hybridisation Threat

Pacific Black Ducks

Our April 2012 talk was presented by Patrick Guay, a research fellow from Victoria University, on the topic of how hybridisation with domestic ducks is threatening Pacific Black Ducks in Australia. Patrick’s area of expertise is in waterfowl ecology and conservation & population genetics and he is well known to our group through his work on the swans and musk ducks on Lake Wendouree. Overall we don’t have a good track record when it comes to protecting birds.

Most of us know about the effect of removal and fragmentation of habitat, particularly on our woodland birds, but have you thought about what happens if some of our common species like ducks start to disappear? If you think about most places we visit where there is water; streams, reservoirs, lakes and swamps we will generally see Pacific Black Ducks. They are one of our most widely spread and abundant ducks.

Patrick began by showing us two specimens, a pure Pacific Black Duck, and a hybrid, which was a paler brown and had less distinctive markings. The Victorian Field Naturalists provided funds for the specimen to undergo taxidermy so Patrick had good examples to use at talks and displays. Patrick then outlined many examples of hybridisation such as dingo x dogs, domestic cats x wild cats, rainbow x apache trout in America, ruddy duck and whiteduck in Europe, Grevillea rosmarinifolia x indigenous grevilleas and Sydney Golden Wattle (Acacia longifolia subsp. longifolia) and coastal wattle ( Acacia longifolia subsp. sophorae).

The Pacific Black Duck, Anas superciliosa is closely related to the Mallard, A. platyrhynchos, which was introduced into Australia from the Northern Hemisphere in the late 1800s. The two species have similar food and habitat needs. Throughout the world Mallards hybridise with many native duck species and the potential threat to local duck populations is well recognised.

When these two species interbreed the Mallard strain is dominant and in successive generations the characteristics of our native Pacific Black Duck may be lost. The Mallard are more sedentary birds and the Pacific Black Duck hybrids may not be as able to survive in the long term as pure native duck species are nomadic especially in times of drought. Hybrids of waterfowl are common, many occur in the wild, and many are fertile. If the situation resulted in sterility as in the case of mules, which are crosses between horses and donkeys, then there would be fewer problems.

Mallard are the main culprit in hybridization and there are recorded crosses between Mallards and 40 other species of ducks in the wild, a further 20 in captivity, and 17 of these are fertile wild crosses. In Australia wild Mallards are rare, only being found around the SE and SW coast, we mainly have the domestic duck which is a descendant of the Mallard.

People seem to have an urge to set their unwanted ducks free on local ponds and lakes. These urban ponds are now acting as a Mallard gene pool reservoir. Mallards are able to out-compete male Pacific Black Ducks because they are dominant and don’t rely on courtship behaviour. The male Mallard forces itself on female Pacific Black Ducks.

The Mallards also breed earlier in the season than Pacific Black Ducks. Mallards breed with other Mallards first and as there are an excess of Mallards they then breed with Pacific Black Ducks. In New Zealand their pure Black Duck has disappeared through hybridization after the Mallard was introduced in the mid 1800s. The first hybrid appeared in 1917 and by 1980 there were less than 5% of the black ducks left.

There is a similar story in Lord Howe Island after the Mallard self introduced. Currently there are no management strategies to deal with hybrids and this is partly to do with legislation. In Victoria a species that is kept as a domestic animal cannot be named as a noxious species. Wild varieties of Mallards are declared noxious but when it comes to the hybrids local council and others don’t seem to want to get involved apart from an occasional discrete cull.

There is the burden of proof as to who owns the duck and so it is difficult to organise a coordinated removal of hybrids from an area. If we still want to have our Pacific Black Ducks then we need to take action. There was lively discussion and some interesting ideas on what form of action is required. Probably the first step is to raise awareness as Patrick so ably does. We need to educate others on what is at stake. Perhaps we should begin by having discussions locally with the City of Ballarat to see if they will erect some signage around Lake Wendouree and the dams in Victoria Park to advise people against dumping their ducks. Releasing these ducks should be made more difficult. Anyone have a good recipe for duck pâté? Elspeth Swan