17 de octubre de 2021

Recognising mallard x pacific black duck hybrids

Came across this great article that includes an appendix with photos of several hybrid features, scaling them 1-6. 1-2 Being genetically pure Pacific Black Ducks, 3-5 hybrids and 6 being mallards. Features include facial markings, speculum features and leg colour.

https://notornis.osnz.org.nz/system/files/Williams_66_45-63.pdf

Anotado en 17 de octubre de 2021 a las 12:42 AM por jason_graham jason_graham | 0 comentarios | Deja un comentario

11 de septiembre de 2021

Genetic Threat to Pacific Black Ducks in Tasmania

The following was published in Birdlife Tasmania's Yellow-Throat Newsletter (Issue 115 Spring 2021, page 13): https://birdlife.org.au/images/uploads/branches/documents/TAS_-_Yellow_Throat_Number_115_Spring.pdf

Hybridisation is a relatively unknown impact on native duck species. But as proven in other parts of the world, it can be a threat to a species, especially when combined with other threats such as shooting and habitat loss, as it can result in the species’ loss of genetic identity.

In Tasmania, hybridisation (or cross-breeding) occurs between introduced Mallards and native Pacific Black Ducks (PBDU). Mallards and PBDUs are closely related and can interbreed easily, resulting in fertile hybrid offspring. There are commonly expressed traits (eg orange legs, blotchy bills, varying feather patterns), but the traits can be subtle and variable. Due to the success of these hybrids, it can be difficult to spot a genetically pure PBDU in the Derwent Estuary and many other Tasmanian waterways.

PBDUs can’t be shot in residential areas, but it seems that the vast majority of urban waterways in Tasmania are dominated, or at least populated by, numerous feral ducks and hybrids. This means that when PBDU populations are safe from shooters, they are still vul- nerable to competition and interbreeding with the more dominant and aggressive Mallards. Male PBDU courtship displays can’t compete against the more dominant male Mallards, who are much larger than PBDUs and will force themselves on native female PBDUs.

Mallard numbers around Tasmania are supplemented by dumped pets and supported by inappropriate feeding by members of the public. They tame easily and readily thrive in human landscapes. When there is a stable food source provided by humans, their numbers can increase rapidly and quickly exclude smaller native ducks.

In New Zealand, it is now very difficult to find a genetically pure PBDU due to the extent of Mallard hybridisation, and PBDUs on Lord Howe Island have been replaced by hybrids. Several other duck species around the world are endangered by Mallard hybridisation, and species on islands or smaller geographical areas are at greater risk of extinction.

Here in Tasmania, we are in a unique situation where we can create safe habitats for native ducks close to urban centres. Often, we need to create reserves and national parks to protect habitats, but in this case the impact is oc- curring in suburbs and town parks. Residential areas provide refugia for native ducks, but feral ducks (including feral geese and Muscovy ducks) need to be removed to minimise the threat from hybridisation.

Important urban wetlands such as Gould’s Lagoon and Lake Dulverton are already being impacted by feral waterfowl, and this impact is only going to increase if Mallard numbers are not controlled. All native ducks will benefit from the removal of the larger, aggressive Mallards, but PBDUs in particular will have the bonus of reducing the threat to their genetic identity.

To help our native ducks, it is critical that people stop feeding them! No human food can beat a native duck’s natural diet, and swapping bread for greens still supports feral ducks and geese. Placing containers of water out also only supports feral ducks. To best look after our native Tasmanian ducks, we need to enjoy them by identifying them, learning about them, and by simply watching them going about their business.

Anotado en 11 de septiembre de 2021 a las 11:56 PM por jason_graham jason_graham | 0 comentarios | Deja un comentario

How Mallards are Threatening the Future of Pacific Black Ducks

The following was published in the September 2021 issue of The Hobart Magazine (page 38):
https://issuu.com/stephaniewilliams52/docs/thm_september_edition_sml/38

Everyone loves ducks, but how many people know what a “duck” actually is? In Tasmania, we have 11 species of native ducks, either full time residents or occasional visitors. Sadly for our ducks, they’re not as famous as a lot of our other native birds. A recent Victorian study found that only 1 in 6 Victorians can name a single native duck species, and Tasmania wouldn’t fare much better. The image of a local duck that you have in your head right now might not even be an Australian duck!

Around Hobart, we are lucky to have plenty of suitable habitat for some of the more common duck species, like the tree-nesting Australian Wood Duck, the elegant Pacific Black Duck and the handsome Chestnut Teal. Some are less common around Hobart, like the Australasian Shoveler with their massive bills, the very unique looking Musk Duck and the oddly-named Hardhead. Then there are the visitors to the Derwent Estuary, like Freckled and Pink-eared ducks. Both of which look completely different from a standard “duck.”

When we picture ducks, it’s probably safe to say that most of us picture a webbed-footed water bird that’s either green and grey, light brown, all-white, or a combination. Maybe you don’t have a specific duck in your head right now, but rather the image of multiple yellow bills pecking at your hands for more bread. I, like most Tasmanians have memories of feeding these ducks as a child (Richmond was our local), and many municipalities in Tasmania have their go-to spot for feeding tame ducks. These ducks have a name: Mallards.

Mallards are a Northern hemisphere species, and have been introduced to Australia and New Zealand. Feral duck populations in Tasmania are a mix of wild and domestic mallards (think white farm ducks). Mallards are bigger and more aggressive than natives, and when there is a stable food and water source (Bread, lettuce, tubs of water etc.), their numbers can explode! This is bad news for our smaller, more timid native ducks. It doesn’t take long for mallards to push out the smaller natives, who just can’t compete with their numbers and size.

More and more people are becoming aware of the impacts of feeding bread to wildlife, which is fantastic. Feeding ducks bread leads to all kinds of health, behavioural and environmental issues. What is not often advertised, is that feeding ANY kind of food to ducks is harmful. No human food can beat the natural diet of insects and plants that ducks feed themselves on while dabbling or diving, and swapping bread for greens still supports populations of feral ducks. Even simply putting out a tub of water may seem like a harmless way to help ducks, but the only species who benefit from this are feral ducks, who prefer to stay in their local area and essentially take it over. Native ducks on the other hand simply fly away if they’re thirsty or hungry. The best way to help all Tasmanian ducks, is to let them find their own food and water.

What concerns me the most about the number of mallards in Tasmania, is the hybridisation impact on native Pacific Black Ducks (PBD). Mallards and PBDs are closely related and can interbreed easily, which results in lots of fertile hybrid offspring. Crossbreeding is very common, with larger male mallards skipping the courtship rituals of PBDs and simply forcing themselves on native female PBDs. Some PBD x mallard hybrids are easily spotted by their bright orange legs, blotchy bills or larger bodies, but many of the traits are subtle and take practice to identify. Due to the success of these

hybrids, it’s difficult to spot a genetically pure PBD in the Derwent Estuary and many other Tasmanian waterways. This hybridisation has resulted in the near-extinction of lots of duck species around the world. In New Zealand, the problem is so widespread that native PBDs have almost completely been replaced by hybrids! PBDs are now rare on Macquarie, Lord Howe and Norfolk Islands due to mallard cross-breeding. Around the world, the mallard hybridisation problem is always more severe on islands. The fact that Tasmania is smaller than New Zealand is very concerning for the future of our Pacific Black Duck.

To best look after our native Tasmanian ducks, we need to enjoy them by identifying them, learning about them, and by simply watching them going about their business. As a reformed duck feeder, I guarantee that this is much more educational, rewarding and fun. RPSCA Victoria and Birdlife Australia have created a great website that I encourage everyone to check out, all about our Australian ducks: www.discoverducks.org.au.

Jason Graham

Bachelor of Natural Environment & Wilderness Studies
Registered native duck carer

Anotado en 11 de septiembre de 2021 a las 11:49 PM por jason_graham jason_graham | 1 comentario | Deja un comentario

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