Mice recently damaged a prison but the invasion of rodents has hit Australia hard for several months now. The situation may last for another year.
The Wellington Correctional Center has to transfer 420 inmates and 200 staff to other detention centers by the end of the month. Mice damaged internal wiring and ceiling panels in the prison facility in New South Wales, a region hit by a giant mouse plague with Queensland.
"The health, safety and well-being of staff and inmates is our number one priority so it’s important for us to act now to carry out the vital remediation work", said Peter Severin, the Corrective Services NSW commissioner.
New South Wales and Queensland states have been hit by a mouse plague for months now, invading prisons, farms, schools and even homes, from the cupboards up to the beds.
At home, mice eat or chew pretty much everything: a carpet, the wooden floor, the ceiling insulation or the electric wires. Although seeing mice have become a common thing among the population, some prefer to wear pants than having a mouse scrambling on their legs. But the smell of death, urine and faeces remains pungent. It affects mental health and morals too, especially the farmers', who also see their crops being destroyed.
Favorable conditions for mouse breeding
Some farmers even burn their production as it has become unsalable and only feed mice. If mouse urine hasn’t infested the harvest, lots are returned because corpses are found in the seeds. It affects machinery, too. Some were on fire because mice chewed electric wires. New South Wales Farmers' Association estimated the plague cost $1 billion AU ($749 million US) in damage to grain growers. The state government so far provided $150 million AU ($112 million US) in support to the farmers.
Australia lives a mouse plague every decade or so, but this one may be the worst in thirty years.
For once, the last harvests were good after several years of drought. As farmers stocked hay for their cattle, it also supplied food for the mice. The conditions have indeed been favorable for the rodents. The droughts in the last four years disseminated their main predators. But mice have a quick reproduction cycle. A mother can give about 10 offsprings every three weeks so they can recover from difficult conditions pretty fast. Last year, the mild, moist summer in December 2019-February 2020 helped yielding a good production for farms and early breeding for mice. Mice continuously bred from the summer until spring. Moreover, for environmental concerns, farmers stopped burning their fields at the end of the harvest to clear the land, which gave more food and shelter for the rodents with the remaining stalks. With no predators, good breeding conditions and abundant food, mice proliferated and started to show up in September-November 2020, during spring.
Environmental and health concerns for the use of poison
To fight the invasion, shops have soon been short of traps and baits. Farmers can use poison: wheat grain coated with a zinc phosphate toxin. At first, it proved ineffective because of the quantity was diluted over all the mice. The state government allowed to double the dose. But the use of poison has also environmental concerns. The seeds may be eaten by other animals, like birds. Dozens of galahs were found dead because of the poison.
The overall impact on the entire ecosystem remains unknown. Some fish have added mice in their food habits. Videos could be seen with Murray cod fish regurgitating dozens of mice from their stomachs. Multiple powerful owls, a species native to Australia, mysteriously died. They suffered from internal bleeding, which is exactly what a powerful poison is supposed to do to mice.
The bromadiolone is currently banned for outdoor use in Australia but the New South Wales government asked for an emergency permit. This poison is an anticoagulant, which in the end would be the equivalent of "napalming" the mice, said Adam Marshall, the state Minister of agriculture. Except that the poison can remain toxic for 6 months in a dead body. The zinc phosphate, the standard poison, turns into phosphate gas and its toxicity is gone in a day.
All hope that the coming winter months will be cold to stop the plague. It will also buy time for the fight. But the Commonwealth Scientific and Industrial Research Organisation warned that the situation could last two years. As the population is large and food remains abundant, breeding could even accelerate next year. Or the population has reached a peak and diseases and cannibalism will bring an end to the plague.
- Murray Cod are being found with a large number of mice in their stomachs, Twitter, June 2021, Free access