Cat Eradication

A CBC “Off the Beaten Track” episode in which I talk about what happens when you bring in cats to eradicate mice. Originally aired on September 22, 2000 on CBC Radio’s Mainstreet program in Prince Edward Island.

The Marion Island Cat Eradication Program

Introduction: In 1949, five domestic house cats were introduced to Marion Island to help control a problem with house mice.  By 1977, these five cats had multiplied to 3,400 cats and had eaten several bird species to extinction.  This situation begat the “Feral Cat Eradication Program,” which, over the course of 19 years eliminated all of the cats from the Island.  This is their story.  WARNING TO AUDIENCE: This feature contains discussion of the killing of house cats.  Sensitive viewers and cat lovers may wish to go away for 5 minutes.

The House Mouse Problem

• The word mouse has no scientific meaning – it’s used generically to describe small rat-like rodents.
• The house mouse is one of a greater family of rodents that includes mice, rats, voles, gerbils and hamsters.
• Your average house mouse is brown or gray, can be up to 8 inches long, including their tail.  
• House mice mature quickly, and can mate 2 to 3 months after birth; gestation takes about 3 weeks, and litters can include up to 12 young.
• The house mouse is native to Eurasia, but has been spread around the world.
• If you do the math, you can see that two mice can produce many millions of ancestors in rather short order – two mice mating can result in 2000 mice six months later.
• Sometime around 1818, sealers using Marion Island as a base inadvertently introduced house mice to the Island.
• House mice feed on invertebrates, which are otherwise an important part of the Island’s food chain.
• And house mice seek the food and shelter of human dwellings, so the mice became a problem for the people manning the South African weather station on Marion Island.

The House Cat “Solution”

• The house cat is a member of a family of animals that includes leopards, cougars, and pumas.
• Your average house cat weighs 6 to 10 pounds, and is 21 to 28 inches long.
• Cats reach puberty at 9 or 10 months, can have up to 3 litters a year, and an average litter contains 4 kittens.
• We humans, it is said, first domesticated cats about 3,500 years ago when Egyptians used them to protect their granaries from mice.
• And in 1949, the South African residents of Marion Island decided to introduce house cats to the Island for the same reason – to rid the island of the house mice that had been there for almost 150 years.
• And so five cats (a neutered orange male tabby cat, a black and white female, and 3 kittens) were brought to Marion Island in 1949.
• How naïve they were…
• Two unexpected things happened:
• The cats liked eating birds more than they liked eating mice – and were eating some species of birds to extinction
• The cats multiplied (maybe not so unexpected!)
• A feral cat is simply a sort of cat that, once domesticated, has returned to the wild.
• The result was that by 1977, there were 3,405 feral cats on Marion Island, and the cats were causing far more ecological damage than the mice they were brought to control.

A Note about Feral Cat Eradication

• The problem of feral cats is one we see all over the world – a world where people don’t spay or neuter cats, and where they thoughtlessly abandon their domestic cats on the edge of town.
• In many cities, their any colonies of feral cats, and these colonies are blamed – rightly or wrongly – for everything from spreading rabies, spreading disease, and eating birds.
• There are two strong factions in the “feral cat problem” world:
• The eradicators think that we should gather up feral cats and kill them.
• The trap-neuter-vaccinate-release people advocate trapping cats, spaying or neutering them, vaccinating them against disease and then releasing them back to the wild.
• In 1977, it was decided to take the eradication route, and thus began the “Marion Island Cat Eradication Program.”

Marion Island Cat Eradication Program

• Step one was to introduce feline panleucopenia into the cat population.
• Feline panleucopenia, commonly known as distemper, is an extremely contagious virus that is, roughly, “the flu for cats.”
• The symptoms are similar to those of the flu in humans: coughing and sneezing, vomiting, and diarrhea.
• It rarely lasts for more than a week, but it has a very high mortality rate.
• Feline panleucopenia was introduced into the cat population on Marion Island, and it killed a lot of cats: by 1982, the population was estimated to have shrunk from 3,400 to 615.
• Then the cats developed immunity to the virus, and with less competition for food, cats with immunity survived and multiplied.
• In 1986, with the population on the rise again, it was decided to hunt the cats as a secondary measure: eight 2-man teams using spotlights and 12-bore shotguns killed approximately 803 cats this way.
• Hunting proved not effective enough to eradicate all of the cats.
• In 1989 and 1991, traps were used to try and capture the remaining cats.
• In April 1991, only 8 cats were trapped.
• It’s now believed that cats have been completely eradicated from Marion Island…
• 19 years later!

The Situation Today

• Now that the cat problem has been solved, researchers are turning again to the problem of house mice.
• Biologist Charl Louw is on Marion Island this year doing research on the house mouse problem, looking at population size and growth, trapping, marking, and releasing mice.
• And the Marion Island Cat Eradication Program is held up by the anti-eradication advocates as an example of why cat eradication won’t work in urban areas (if it took 19 years in a closed system like Marion… etc.)