Mouse plague: Bromadialone will wipe out mice, but it will also poison eagles, snakes and owls
(MENAFN – The Conversation) It’s the smell that strikes you first. The smell of urine and rotting bodies. Then you notice other signs: portholes and squeaks, small corpses leaking blood, tails sticking out of hubcaps.
If you have experienced one, you have seen this and smell the stench of the dying mice of poison bait.
As a desperate measure to help tackle the mouse plague that was devastating rural communities in New South Wales, the state government yesterday. This is bait that is generally illegal to deploy on the scale proposed.
It’s a bad idea. While bromadiolone effectively kills mice, it also travels up the food chain to poison predators that eat mice and other species. And these predators, from goannas to goannas, come in droves to feast on their abundant prey.
When your prey is everywhere
Animal pests in Australia are fueled by the “boom and bust” in rainfall.
We have natural, flood-induced population explosions of the native long-haired rat, accompanied by booms of letter-winged kites, their predator. We also have locust invasions when the conditions are right, leading to invasions of antichinus or locust-eating mice.
we have had terrible wounds from the introduced house mouse (Mus musculus). But it has rarely been so bad, with conditions currently looking worse than the last plague of 2011, which caused more damage to crops alone.
Large numbers of birds of prey – nanking kestrels, black-shouldered kites and barn owls – often feast on plague mice.
Snakes, goannas, native carnivores such as quolls, feral cats, and foxes also benefit from the abundant food. Pets, especially cats and some dogs, are also very likely to consume mice under these conditions.
Poison the food web
Placing poison baits is one way people are trying to stop mouse infestations and outbreaks. So-called “anticoagulant rodenticides” are divided into first and second generations, depending on when they were first synthesized and differences in potency.
Wedge-tailed eagles are among the predators that take advantage of house mouse plague. Shutterstock
The second generation anticoagulant rodenticides are higher than the first generation and are fatal after a single meal. First-generation rodenticides, on the other hand, require rodents to feed on them for consecutive days.
But mouse-eating predators are heavily exposed to second-generation rodenticides. For most animal species, the lethal doses of rodenticide are not yet known.
One from 2018 documented the poisoning of 31 species of birds, five mammals, and one species of reptile. Second generation aniticoaugulant rodenticides have been implicated in the deaths of these animals.
Our urban reptiles found from 2020 are also highly exposed to second generation rodenticides. This includes mouse-eating snakes, called dugites, which contained up to five different rodent poisons.
We have also found poisons in tiger frog-eating snakes and omnivorous bobtail skinks that eat fruit, vegetation, and snails. This is even more concerning as it shows how second generation rodenticides can saturate the entire food web, affecting everything from to.
Bobtail skinks do not eat poisonous mice, but they have always been found with poison in their systems. Shutterstock Bromadiolone is particularly dangerous, even for humans
The New South Wales government has secured bromadialone bait as part of its regional communities program.
Five thousand liters of poison about 95 tonnes of grain, and the government will provide it free of charge to primary producers once federal authorities approve its use.
The use of bromadiolone is generally limited in and around buildings. But given the widespread impacts on wildlife, using bromadiolone on the scale proposed will do more harm than good.
Previous research with bromadialone has shown that residues persist for up to 135 days in carcasses of (another rodent species). In international studies, bromadiolone has been present in the livers of a multitude of birds of prey, including a range of species from owls, red kites, hawks, and golden eagles.
Humans can also be exposed by eating the eggs of chickens that ate the mice. Shutterstock
And this is not only a problem for wildlife, they are also at risk of exposure. For example, we may be exposed by eating eggs from chickens that feed on poisoned mice, or more directly by eating other animals that may have ingested poisoned mice.
A examined chicken eggs intended for human consumption and detected bromadialone in the eggs between five and 14 days after the chicken ingested the poison. It is not yet known how many of these eggs we would have to eat to get sick.
So what are the alternatives?
There are very effective first generation rodenticides that provide viable solutions for managing mouse outbreaks. They may take a little longer to kill the mice, but the result is that they do not stay in the environment. A 2020 study found that house mice in Perth were first-generation rodenticides, suggesting they are indeed lethal.
Another approach has been to use zinc phosphide, a poison that is unlikely to secondarily poison other animals that eat the poisoned mice. However, zinc phosphide is still extremely toxic and will kill sheep, cows, if directly eaten.
Deployment of double strength zinc phosphide may be the lesser of ailments causing secondary poisoning, but only if used with great caution.
And another way to help control mouse plague is to limit food resources for mice on farms. Farmers can downplay, and Australia should invest in research into what is less permeable to mice.
Mouse outbreaks are a regular cycle in Australia. Natural predators not only help create healthy natural ecosystems, but they also help control mice. Second generation rodenticides will only destroy and weaken the predator populations we need to help us fight the next plague.
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