VISIT Kakadu National Park and you will be greeted by the resonating honking from the thousands of magpie geese (Anseranas semipalmata) which flock here in the wetlands and swamps.
About eighty per cent of the Australian and likely the global population of large black and white magpie geese live in Kakadu during the dry season. They are an important source of food for the Indigenous community, as well as being culturally significant. However, according to CSIRO research, even though current magpie goose populations are large, predicted sea level rises could see the population crash as saltwater inundates their seasonal habitats.
“Saltwater inundation will affect magpie geese nests and the abundance of their dry season food,” says Dr Leo Dutra, CSIRO Research Scientist and lead author of a paper on how sea level rise will affect socio-ecological systems in the region.
This is of particular concern to Traditional Owners.
“Aboriginal people see magpie geese as an indicator of wetland health. When we hunt magpie geese we also see what they eat, which gives us an indication of the health of the wetlands,” says Peter Christophersen, Aboriginal Land Manager and co-author of the paper.
“Livelihoods of Aboriginal people in Kakadu depend on healthy freshwater systems. Magpie geese are one of the numerous values that will be affected by rising seas.”
Threats to magpie geese
Magpie geese depend on freshwater wetland plants. In the dry they eat bulbs of water chestnuts (Eleocharis dulcis) which allows them to put on fat for the wet season, ensuring they are ready for breeding. In the wet season, water chestnut stems are used to build floating nests while wild rice (Oryza sp.) provides food for emergent goslings and adults.
Because Kakadu is very low lying and susceptible to king tides of up to seven metres, a small change in sea level will have a big impact on the ecology of Kakadu. King tides currently push saltwater into the upper reaches of rivers around twice a year, usually July and December.
Sea level rise may result in king tides pushing saltwater further upstream and saltwater inundation will become more frequent and sustained.
According to the Intergovernmental Panel on Climate Change, sea levels are predicted to rise by 0.7 metres by 2070.
Recently-published CSIRO modeling shows that this will result in 42 percent of Kakadu freshwater wetlands being inundated with saltwater by 2070, and 65 percent of Kakadu freshwater floodplains being inundated by 2100.
As a result, fresh water plants won’t have time to recover and more saltwater plants like mangroves may take their place and attract different animals.
The nesting and feeding habitats of the magpie geese along with important cultural, hunting, fishing, and gathering sites will all be affected by saltwater inundation.
“Sea level rise may change the shape of rivers and creeks, and new saltwater plants will bring different animals to the floodplains, “ says Dutra.
Park managers are already dealing with the threat of feral animals and weeds, but sea level rise has now been added to the challenges they face.
Says Christophersen: “A saltwater flush every now and then might be beneficial for water chestnut, but if saltwater inundation occurs too often or becomes permanent, it will kill everything that grows in freshwater.”
“Magpie geese are very adaptable birds. We can see adults changing their eating habits when their preferred food is not available. Our concern is about the availability of quality nesting material, food for goslings and how sea level rise combined with other pressures, such as hunting, might affect magpie geese populations.”
Impact on customary harvesting
Magpie geese are an important resource in Indigenous customary harvesting.
Both the bird and eggs are eaten, however customary harvesting is not just about food – magpie geese also have cultural and spiritual significance.
“There has been a long history of harvesting the birds since the fresh water floodplains evolved several thousand years ago. Both the geese and their eggs are a really valued food source and also have a whole suite of social and cultural values attached to them,” says Emma Ligtermoet, PhD student at the Australian National University and CSIRO.
“In an Aboriginal worldview there are protocols to follow that guide the customary harvesting of magpie geese. They include for example the methods of hunting, cooking, disposal and sharing of harvested adults or eggs. This belief system incorporates consequences for breaking these rules, like the risk of a poor harvest the following season," says Ligtermoet.
As part of her PhD research Ligtermoet spoke with people both in Kakadu and West Arnhem Land to find out what Indigenous people thought about the risk of ongoing sea level rise and found a spectrum of perspectives.
“Some people feel confident in adapting in terms of being able to move to where the animals move – that process of adaption that Aboriginal people have been doing so long,” says Ligtermoet.
“However many people recognise existing environmental pressures are reducing their capacity to hunt. Some people are quite concerned about the impacts of salt water inundation transforming fresh water places and whether there are sufficient alternative areas to access,” says Ligtermoet.
If the sea level does rise, magpie geese hunting grounds might either be lost or emerge in another area, but this area may be looked after by a different clan.
“People have their own clan estates - the country they are responsible for looking after and managing. Some estates may be more affected than others. Maintaining strong relationships between clans is also important for supporting people’s abilities to adapt to climate change impacts,” says Ligtermoet.
Responding to climate change
Understanding floodplain ecology and potential impacts associated with sea level rise on freshwater floodplains and Indigenous values is the first step towards responding to the threat of climate change.
While it is alarming that the magpie geese population in Kakadu may plummet in fifty years time, CSIRO modeling provides an advance warning that will enable Traditional Owners and park managers time to respond.
“A combination of monitoring programs and incorporating Indigenous knowledge into management will help us to better understand the ecological processes that affects this culturally valued species as well as others like the northern longneck turtles,” says Christophersen.
Magpie geese are one species among a number of freshwater animals and plants that have significance for Indigenous people, not just for subsistence but a range of cultural values. The potential loss of freshwater wetlands and the geese they support, risks impacting both Indigenous livelihoods and the ecological character of Kakadu’s wetlands.
By understanding the impact of saltwater inundation and how it affects magpie geese populations, and other critical values in Kakadu, Dutra is hopeful that this in turn will enable Indigenous people to continue to live on country in future.