The mouse plague in Western and South Australia is a devastating issue that has been wreaking havoc on the region for months. It's a complex problem with no easy solution, and it's important to understand the reasons behind it and the potential consequences. Here's a deep dive into the situation, with a focus on the new double-strength bait being introduced as a potential solution.
The Breeding Ground
The mouse plague began with the summer grain harvest in Western Australia. Agronomists and farmers raised the alarm in February, but the scale of the problem was already apparent. Mice breed rapidly, with the ability to give birth to up to 10 offspring every 20 days, and they can fall pregnant again immediately after. The perfect storm of conditions, including a record harvest, fewer sheep to clean up spilled grain, and summer rain, created an ideal breeding ground.
The Impact
The impact of the mouse plague is far-reaching. In towns like Northampton and Morawa, mice infestations are so severe that they've spread to public buildings and homes. The surrounding farms are crawling with mice, and community leaders are concerned about potential disease outbreaks. The Department of Health has issued a public health alert, urging increased hygiene measures.
Farmers in South Australia, Western Australia, and parts of northern NSW are experiencing unusually high mouse populations, with estimates of more than 8,000 mice per hectare. The citizen science website FeralScan confirms the presence of mice in every grain-growing state, from west of Brisbane to north of Sydney and close to the Adelaide CBD, with extensive hotspots in WA.
The Standard Bait's Limitations
The standard bait used by farmers contains 25 grams per kilogram of zinc phosphide, a toxin that requires the mouse to eat two or three grains of poisoned wheat to die. However, in fields with abundant food sources, mice may only eat one poisoned grain, feeling sick but not dying. This raises concerns that the mice may learn to avoid the bait, and the large population size means that even if half are removed, the remaining mice will quickly breed and rebuild their numbers.
The Double-Strength Bait
Recognizing the limitations of the standard bait, the Australian Pesticides and Veterinary Medicines Authority (APVMA) issued an emergency permit for double-strength bait. This new bait is more effective because it only requires the mouse to eat one poisoned grain to die. While this should bring mouse numbers down quickly, it's important to note that the bait can only be used on farms, not in urban areas, and it's not a silver bullet solution.
Environmental and Health Risks
The CSIRO's mouse expert, Steve Henry, explains that zinc phosphide doesn't bioaccumulate, meaning most of the toxin is used up by the mouse, and what's left dissipates into the environment. The risk of animals eating poisoned mice and getting sick is considered low. However, there is a concern that birds, such as parrots, may eat the poisoned grains, potentially leading to poisoning. The APVMA has imposed strict conditions on the emergency permit to protect non-target species.
The Damage Caused
The mice are causing significant damage to grain crops, with farmers having to re-seed their paddocks due to mice vacuuming up seeds and chewing on growing crops. They're also damaging cars and farm machinery, eating wiring and hoses, and spreading into towns where food-based businesses are affected. The mental toll on people trapping and baiting the mice for months is also a significant issue.
The Way Forward
Mouse plagues typically end due to a combination of factors, including food shortages, disease, and cold weather. The introduction of the double-strength bait should help reduce mouse numbers, but it's not a long-term solution. Residents will need to continue trapping and baiting the vermin, and the impact on communities that rely on wildflower tourism in winter remains to be seen.
In conclusion, the mouse plague in Australia is a complex and devastating issue. While the introduction of double-strength bait is a step in the right direction, it's a temporary measure. The long-term solution will require a multi-faceted approach, addressing the breeding grounds, food sources, and the impact on affected communities.
