The South Farallon Islands has a big rodent problem. It has recently become
the most rodent-dense island in the world.
And the U.S. Government had 49 possible solutions. Deadly solutions.
Every acre of the island, which lies 27 miles off the coast of San Francisco, contains 500 European house mice. The island isn’t inhabited by humans, but those who visit to study the island’s ecosystem say that things have gotten so bad that the ground often seems to be moving.
It’s not only creepy, but it’s dangerous to the native ecosystem and threatens the native animals, specifically the ashy storm-petrel (Oceanodroma homochroa) and the Leach’s storm-petrel (Oceanodroma leucorhoa).
“Invasive house mice are taking a serious toll on the seabirds and other wildlife of the Farallon Islands,” Anne Morkill, manager of the San Francisco Bay National Wildlife Refuge Complex, said in a statement. “The ecosystem on the islands is out of balance. We want the public to give us feedback on our proposals for eradicating the mice and restoring that balance.”
That’s why the U.S. Fish And Wildlife Service has crafted a 650 page report on how to get rid of these pesky mice. They ended up with three options: 1) doing nothing, 2) removing the native species, dropping one of two rodent-killing poisons all over the island, then return the native species.
But, the report first rejected 47 other proposed extermination methods:
- Eradibait — a non-toxic, natural food-based rodenticide that completely blocks the digestive system of the mouse, sending them hiding into a coma and eventually death. This probably won’t work because it needs to be the only food source available to the mouse, it can’t get wet, and will .
- Snap Trap — snap traps aren’t able to capture and kill enough of the mice to be effective, and take a lot of personnel efforts — 5,000 traps being checked daily for weeks, or even years, on end.
- Live Trap — like snap trapping, live traps would require an insane amount of manpower.
- Immunocontraception — this means administering birth control to the mice. The problem? No such rodent birth control even exists. And if it did, it would need to be administered for years, since mice live 18 months.
- Disease — a fatal disease would be introduced to the island that would only kill the mice, but an acceptable disease hasn’t been identified yet.
- Genetic Engineering — releasing genetically modified mice into the island to mess with the natural population, say, making them only able to produce sons. This is also only theoretical, and wouldn’t be possible for another 5 to 10 years at least.
- Introduced Non-native Predators — this would let cats loose on the island to kill the mice, though you’d think the cats would then become an issue.
The rest are rodenticides. These chemical compounds kill within a few hours (acute), days (subacute), or more than a few days (chronic, usually by blood coagulation). They can be dispersed from helicopters (aerial broadcast), though bait stations, by hand (workers would have to walk the entirety of the island on foot).
Because of the rough terrain of the islands, all of the hand baiting and bait station options are automatically struck down. Some of the other chemicals won’t work well for other reasons, usually because they don’t meet safety guidelines.
- Aerial Zinc Phosphide (acute)
- Bait Station Zinc Phosphide (acute)
- Hand Zinc Phosphide (acute)
- Aerial Bromethalin (acute)
- Bait Station Bromethalin (acute)
- Hand Bromethalin (acute)
- Bait Station Cholecalciferol (subacute)
- Hand Cholecalciferol (subacute)
- Bait Station Warfarin (chronic coagulant)
- Hand Warfarin (chronic coagulant)
- Bait Station Diphacinone (chronic coagulant)
- Hand Diphacinone (chronic coagulant)
- Bait Station Chlorophacinone (chronic coagulant)
- Hand Chlorophacinone (chronic coagulant)
- Bait Station Brodifacoum (chronic coagulant)
- Hand Brodifacoum (chronic coagulant)
- Bait Station Bromadiolone (chronic coagulant)
- Hand Bromadiolone (chronic coagulant)
- Bait Station Difethialone (chronic coagulant)
- Hand Difethialone (chronic coagulant)
- Aerial Pindone (chronic coagulant)
- Bait Station Pindone (chronic coagulant)
- Hand Pindone (chronic coagulant)
- Aerial 1080 (acute)
- Bait Station 1080 (acute)
- Hand 1080 (acute)
- Aerial Strychnine (acute)
- Bait Station Strychnine (acute)
- Hand Strychnine (acute)
- Aerial Coumatetralyl (chronic coagulant)
- Bait Station Coumatetralyl (chronic coagulant)
- Hand Coumatetralyl (chronic coagulant)
- Aerial Flocoumafen (chronic coagulant)
- Bait Station Flocoumafen (chronic coagulant)
- Hand Flocoumafen (chronic coagulant)
A few of these met all the criteria set out by the EIS, but they haven’t been approved by the EPA for conservation use and rodent eradication:
- Cholecalciferol (subacute)
- Warfarin (1st generation)
- Chlorophacinone (1st generation)
- Bromadiolone (2nd generation)
- Difethialone (2nd generation)
That left only two options, which would need to be dispersed aerially after the removal of the endangered bird species on the islands:
- Diphacionone (1st generation) — this compound is less toxic to birds, but has never been successfully used for rodent eradication, and rodents tend to avoid eating enough of the bait to kill them.
- Brodifacoum (2nd generation) — more than 98 per cent of mouse eradication have used this drug to kill of rodents.
When the mice are gone, the birds can be returned to the island. Other animals that can’t be removed are potentially threatened by the chemicals in these rodenticides.
None of those are as unique as the Navy’s plan to bomb Guam with Tylenol-dosed dead mice to kill off brown snakes that are taking over the island.
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