Photos of fish with mice in their stomachs are spreading across the internet as a mouse plague wreaks havoc in the Australian state of New South Wales.
The plague has been relentless for rural communities in the state, says Steve Henry, a mouse expert and CSIRO researcher.
Photo: CSIRO, CC BY 3.0
Listen to Steve Henry on Afternoons
“In places where [the mice are] really bad, there’s actually wheel tracks on the bitumen that are just covered with mouse spatters... so they are almost like a carpet on the roads,” Steve tells Jesse Mulligan.
“They are in people’s houses; one farmer took 400 out of his house in one night.
“They are destroying haystacks, they’ve destroyed summer crops and now we are flat out trying to protect the winter crop that’s been sown.”
The plague is having a damaging psychological effect, he says.
“One of the really unquantified things about a mouse plague is the psychological effect and people are just weary with dealing with mice all the time.
“They get up in the morning and have to deal with them in the house, and they deal with them out in the paddocks and sheds and they’re there when they get home in the evening.”
The weather conditions which caused the mouse plague are good for farmers in one way, Steve says.
“[These conditions] tend to happen at the end of a run of dry years. When conditions become favourable for growing crops they are also great conditions for mice to breed.
“This year in particular we’ve had a mild, moist summer, so they have continued to breed from early spring right through the summer and into the autumn.”
Concerns have been raised about how poisons used to kill the mice could affect the rest of the food chain.
Zinc phosphide is the usual first line of defence against mice running wild, Steve says.
“Farmers only have one permitted form of control which is zinc phosphide on wheat grain spread at 1 kg per hectare and they spread that through their paddocks as they sow the crop.
“Zinc phosphide is quite a good chemical because the phosphide is converted to phosphine in the acid environment of the mouse’s stomach and goes off through the bloodstream and does major damage to the organs.
“It is used up in the act of killing the animal and what doesn’t get used dissipates into the environment in a gaseous form and so there is no toxin left in the mouse to kill another animal.”
In this sense, zinc phosphide is a relatively benign poison compared to the toxic anti-coagulants permitted for mouse-killing near homesteads, he says.
“After [that has] killed the mouse there is still toxin left in the animals and that can poison other animals that come along and eat those mice.”
Anti-coagulant use is only permitted when occupants can dispose of the dead mice safely to avoid further death of wildlife, Steve says.
As we come into winter, the mouse population should now plateau, he predicts.
As the rate of mouse population increase is determined by how many survive the winter, farmers are hoping for a population crash over the colder months, Steve says.
If weather conditions favour the mice, their population could explode.
“Mice start breeding when they are six weeks old and they can give birth to 6-to-10 pups every 19 to 21 days after that, but the real kicker with them is when they put that first litter on the ground they fall pregnant with the second litter.
“So, while they are weaning the first litter they are gestating the second one and when they pump the first litter out of the nest they give birth to the second one. So, there is no break in pup production through the season.”
Being a mouse expert amidst a plague is keeping Steve busy, and he says he's not squeamish about them.
“They’re just another cool little animal that’s in the wrong spot.”