By Christa Rodriguez || Campus Life Editor

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This past Thursday’s Common Hour speaker, Peter Marra, discussed the negative impacts of cats on biodiversity, based on his book, Cat Wars: The Devastating Consequences of a Cuddly Killer. Marra is the head of the Smithsonian Migratory Bird Center; however, his recent book was formed from work outside his day job.

Marra prefaced his talk by saying, “I didn’t want to write this book.” To him, sometimes scientists get to a point where they see such overwhelming evidence that it would be irresponsible to not make people aware. He confessed that he loves cats and even owns his own. But this does not diminish the fact that they are predators, and, left unattended, their predatory behavior comes out. Left to their own devices outdoors, cats both impact wildlife and spread many diseases by “just doing what comes naturally to them.”

He blame humans as responsible for spreading cats around the world as well as ignoring the problems they cause. Marra argued that we have to be more responsible cat owners, himself included, in order to reduce these issues. The science is a little fuzzy on how wild cats came to be domesticated, but now cats “occur in no native ecosystem around the world,” similarly to pigs and cows. However, they have also reached a popularity in our culture from Garfield to Grumpy Cat that erases their potential harm in the public’s view.

To provide perspective, Marra noted that there are 90 million owned cats in the world. Of those, approximately 66% go outside. Looking at unowned cats, of which there is an estimated 60 to 100 million, comes to a total of anywhere between 90 to 160 million outdoor cats. Marra believes that number is growing. The amount of cats is an issue for biodiversity, especially for birds. He noted that 38% of bird species have declined in the last 40 years. These declines are alarming to Marra, as he said, “If we don’t step in, they’re going to extinct.” In fact, some numbers of a bird species are so low, they are directly threatened by cats. This threat needs to be removed in order to keep these birds in existence.

Furthermore, he added that cats have contributed to at least 63 species extinctions, including birds, reptiles, and amphibians. It is estimated that 1.3 to 4 billion birds are killed by cats per year. But Marra is confident that the real number is closer to 4 billion.

In addition to extinctions, cats also spread parasites and diseases. Marra spoke at length on toxoplasma gondii, which affects both humans and other animals.

One possible solution Marra offers to this cat problem, besides keeping owned cats inside, is treating cats like dogs. It used to be more common for dogs to roam around, carrying rabies and getting hit by cars in the 1960’s in America. Then communities took initiative and became more responsible owners. Marra believes that cats, too, can be kept on leashes when they go outside. Another solution is to build outdoor “catios” for your feline pets. This way, the cat can see the outdoors and breathe fresh air, but they won’t have free reign to roam all over the place.

For unowned cats, Marra suggests that people must stop abandoning their pets as well as neuter cats. He discussed one possible solution, Trap Neuter Return (TNR), which consists of catching a stray cat, neutering and sanitizing it, and releasing it back again. This is problematic to Marra because these cats then are left to die in inhumane ways like getting hit by cars. In addition, the neuter rates must exceed 75% for this method to be successful, which it hasn’t. To him, humans must think about the whole ecosystem that needs to be protected. He made it clear that he is not saying we must get rid of cats, although he did propose that one solution was euthanasia. Marra believes it is OK to kill one species to save another. He noted is already happening in Australia and New Zealand, where unowned cats are being euthanized.

For the time being, Marra remains optimistic to the idea that humans can make positive change, not only for the world at large, but for the betterment of cats as well.

Junior Christa Rodriguez is the Campus Life Editor. Her email is