By Julia M. Zichello

Julia M. Zichello, Ph.D., is an evolutionary biologist who lives on the Upper West Side. 

Almost a year has passed and I can finally write about it. We had two pet rats, and last fall — they died. First the silver one left us in the morning, and less than a week later, I watched the black-hooded rat take its last breath.

The absurdity of being sad about rat death while living in New York City is substantial, and subversive, and oh-get-over-it, and yet. I regularly walk the Upper West Side and spot swashbuckling rats at all hours, but other times I find them squashed. I don’t exactly feel sad about the dead rats I see on the street. But I also don’t feel nothing. They will always remind me of our short-lived, lively pets that I didn’t even want to begin with. But mostly, the dead street rats make me think about life, death, and, somewhere stuffed between the pavement and the pelage — there is something about love in there too.  

Last week, the New York City Council passed a bill that will replace rat poison with rat contraception in parts of the city. It has been dubbed “Flaco’s Law” in honor of the majestic Eurasian eagle-owl that once lived, and died, on the Upper West Side. During Flaco’s time spent living outside of the Central Park Zoo, when he was on the streets, he hunted. His hunting was a sign that even though he was born in captivity, you can never truly take the wild out of the wild.

When Flaco died, the necropsy showed rat poison in his blood. This unfortunate toxic food web will be mitigated by the rat contraception, is the hope. Birds of prey like Flaco, and the many native red-tailed hawks and owls, will no longer take the rat poison to the skies. And the poison also won’t threaten other animals like all the beloved cats and dogs. 

Rat contraception, a product known as ContraPest, works on both male and female rats. The new rat baits will make the rats infertile, but only temporarily (about 45 days after they consume it). But because their lives are somewhat fleeting as it is, the plan is that this will make a dent in the population. And supposedly the formula for the rat birth control is irresistible to rats. Bon appétit. 

Because we already know that rats are clever, and they even have individual personalities — some are bold, others are cryptic — one wonders how the new rat bait will change the collective behavioral vibe of their population. For example, if the bold individuals are more open to trying new things, like the rat birth control, then will the population become less bold, and more hidden? This is how natural selection can work, though the selective pressure in this case is not totally natural because the birth control is created by humans.

There are an accumulating number of examples of evolution in cities where animals astonishingly adapt to the extreme conditions we create. Knowing evolution, I would bet that rats are no exception. Only time will tell. But not too much time, because a rat’s life is short. 

The lifespan of wild rats is typically around one year. A female rat may give birth to up to approximately 72 pups per year. That’s a lot of offspring, which is an evolutionary tradeoff between lifespan and fertility. This relationship between short lifespan and high number of offspring is a survival strategy. Species with short lifespans tend to have more offspring to maximize the number that survive to the next generation. Live fast, have a lot of babies, and die young (or grow old rapidly). 

Rats, like many animals, can live longer in captivity than in the wild. Pet rats usually live around two years. Our rats lived 2.5 years, but that still felt short. Because they can be such charming and intelligent pets, the relationship between their charm and their lifespan is heartbreakingly asymmetrical. It’s the mammalian equivalent of falling in love with a single butterfly. You will probably see the end. 

If you are someone who is a total “Oh No Way” on the rat conversation, then you probably have not read this far. So, I will use this special space for lovers of even the most unlovable pets. If you spend enough time with any living mammal who relies on you for food and water, is it even possible not to end up loving them? When their little ways fill your days and you watch how they move in your human-made world, how they eat — often with gusto, pretty much always adorable — and, of course, their warm, bright eyes. I found myself in awe of the sensory systems of our pet rats. I watched them sniff, I watched them navigate, I saw them socialize, I heard them vocalize. Those dark sparkling eyes really pay attention and can make you feel “seen,” even if it’s just by a couple of old rats.

One important aspect of the new rat initiative is that, if it becomes more widely used, no rats will die due to poisoning. All the rat deaths now will be natural, or as natural as anything can be in a giant human-made metropolis. And not every single rat will eat the contraception, so, of course, the rats will go on. But I will never have pet rats again because pet death is just too painful. I will settle for keeping up with the rat life cycle that plays out on the streets. I will keep my ear to the ground (but not too close), and my heart in a cage. 

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