Cape Town – Mallard ducks, an aggressive alien species, could wipe out South Africa’s indigenous ducks if left unchecked, experts say.
The city council is now assessing dams and other water bodies in the metropole to decide which mallards may be kept – if a permit is granted – and which must be euthanised.
Like all landowners in the country, the city is required by law either to control or eradicate mallards. It is a touchy subject: some landowners, such as those at Century City and Lake Michelle in Noordhoek, have asked the city council to remove mallards from their land, but other residents have shown fierce opposition.
Mallards, introduced for sport hunting, are popular as pets and “ornamental” waterbirds. However, in a bid to save local waterfowl from extinction, the Department of Environmental Affairs has made it illegal to keep, breed, sell, trade or import mallards without a permit.
A relatively recent invader, mallards are now widespread, with between 800 to 2 000 in the metropole. They are native to Europe and North America and outcompete indigenous ducks for food, nesting and roosting sites.
But the real impact of mallards, according to the late Phil Hockey, former director of UCT’s Percy FitzPatrick Institute of African Ornithology, is “more insidious”: the birds can breed with about 40 other waterfowl species, leading to hybrid offspring. The hybrids are fertile and can breed.
In South Africa mallards now breed with the indigenous yellow-billed duck, cape teal, cape shoveller and are thought to breed with the African black duck. If left unchecked, these indigenous duck populations would become extinct, leaving in their place a variety of hybrids.
Hockey wrote in 2010 that mallards appeared to be in the early stages of a “large-scale invasion”.
“Mallards are probably the most threatening alien bird species in the country today,” he wrote.
Debbie Sharp, from the Department of Environmental Affairs, said yesterday regulations governing invasive alien species published in October under the National Environmental Management Biodiversity Act listed mallards as “category 2”, which meant landowners needed a permit to keep them.
Strict permit conditions required the landowner to ensure mallards were not allowed to spread, so they would need to be kept in an enclosure or have their wings clipped.
“But all feral populations are regarded as category 1b, which means you need to eradicate them,” Sharp said.
“The regulations don’t say how to kill them, but it must be done in the most humane way.”
Louise Stafford, of the city’s environmental resource management department, said mallard hybridisation had devastated waterfowl populations across the world.
In Hawaii, mallard hybridisation had caused the endangered Hawaiian duck to disappear from all but one island.
In New Zealand, mallard hybridisation had led the grey duck population to plummet to 4.5 percent of what it was.
In Madagascar, the endangered endemic Meller’s duck is threatened by Mallard hybridisation.
“We are not eradicating mallards, that is not possible, but we have to control them. Every landowner is compelled to do so by law,” Stafford said.
lThe city asks that all mallard sightings are reported to www.capetown invasives.org.za