Uncovering the secret lives of New York’s rats

New system tracks rats underground to curb disease and learn what they’re up to when nobody’s watching.

If you’ve been to New York, you’ve probably become acquainted with a rat or two. The city’s subway system and sidewalk garbage piles seem to be full of them. But the rats we see are only the boldest, those that dare to venture above ground. To truly understand the rodents we share our cities with—and it is important we do given their capacity to spread disease—we need to learn about the majority that stay out of sight. Rodentologist Michael Parsons and his colleagues have come up with a way to do just that. Introduced in a paper published in Frontiers in Public Health, the method entails tagging rats with implanted RFID (Radio-Frequency Identification) microchips and releasing them back into their original environments. The animals’ activity can then be monitored through data collection stations. 

ResearchGate:  How did you come to specialize in urban rat research?

Michael Parsons: I was presented with the perfect storm of opportunity after I moved to New York from Australia, where I did my PhD and postdoc studies. First, I had a keen interest in terrestrial chemical ecology, or the “scents that make sense” to animals. For rodents, the ability to detect and respond to scents within the environment dictates most behavioral decisions such as where to forage, when to find a mate, or how to find harborage. Second, there was opportunity to meet a need. More than 40 percent of all mammals are rodents, yet less than one percent of all mammalogists are rodentologists. Importantly, these rodents depend on humans for food and harborage. Because of that, they stay close enough to humans to cost our economy $19 billion in food losses and infrastructure damages. They also vector a range of diseases. Third, I met and received training from Robert Corrigan, an internationally-renowned rodentologist whose passion for rats is infectious (pardon the pun) and whose company is captivating.

RG: Why is it important to learn about rat activity in urban areas?

Parsons: It is essential we learn more about rats because, despite their great capacity to influence our society, little is known about their behavior or the organisms they vector. With 75 percent of the world’s population expected to live within urban environments by 2050, there will be more and more people packed into tighter living spaces increasing the risks of communicable diseases vectored by rodents, including Toxoplasma, Salmonella, Lyme disease, Rocky Mountain spotted fever, Hemorrhagic fever and many others. Given that humans generate so much rubbish and wastes for rats to feed upon, and the difficulty of changing human behavior, we must learn how to change rat behaviors, or at least mitigate our risks by understanding what diseases they carry. On top of that, climate change will mean shorter cold seasons, potentially leading to more active rodents and more fleas and ticks.

Finally, in 2014, a group of researchers found 18 viruses new to science among only 133 rats sampled in New York City. Our team cannot understand why are we not answering their call to routinely test these animals and to continually document these pathogens and how they change in populations and individuals over time.

microchip
Researchers use a mobile laboratory to implant RFID microchips. (Parsons et al. in Frontiers)

RG: How does the RFID tagging system you present in the paper work? How does it improve on previous methods?

Parsons: Traditional approaches to studying wildlife, like radio-telemetry and GPS collars, don’t work as well in the city due to the infrastructure in the built environment and the subterranean habits of the animals: subways and sewers. If you cannot go the animals, then you must get the animals to come to you. We accomplish this by barcoding rats with a microchip, then using scents from other rats to recruit them back to the antenna on a regular basis, where they announce their presence, and step on a scale for us to learn about any weight gain or loss and regularly recapture them. Their infatuation with their own scents counter-acts the processes of neophobia and habituation. Because males and female rats are attracted—as well as juveniles—it removes the age and sex bias inherent in most trapping.

RG: What did you learn about rat behavior while testing the system?

Parsons: People who see rats in public often form generalizations about the entire species based on a few observations of the boldest of the bold, rats like the ones in the YouTube videos that seem to go viral every summer. To truly understand rats however, they must be observed at the individual level. By microchipping rats, we can learn about variability within the population. For instance, among our populations, we learned how the alpha male hunted, when the omega males came out, and when females foraged. This is something we would not have known without the microchips.

Our system was designed to allow us to study the variation among rats as individuals, not a species. It will allow our colleagues to collect serum, ectoparasites and DNA samples from the same individual over an extended period of time, so that we can learn about any new pathogens, where and when they are being introduced into the population. Our system has been successful in this regard, though we are open to changes to streamline the process.

RG: How does the rat population in New York compare to other cities? Is there demand for this technology elsewhere?

Parsons: No one knows. Estimates vary widely from 2-32 million rats in the five boroughs of New York City. Most rats are hidden and they don’t announce their presence often. Furthermore, due to social concerns like fear of fines, many people don’t report rats near a business or residence. Rat populations can also vary widely from year to year and season to season. Baltimore and Vancouver have also been extensively studied for rats, however the interest in rats does not necessarily relate to the population size. Our technology with RFID and a mobile laboratory is only a proto-type or model for what public health officials in large cities worldwide may wish to adapt. Hopefully we inspire others to improve upon our start.

rfid system
RFID reading station with sensor, data logger, system control unit. (Parsons et al. in Frontiers)

RG: Do the human inhabitants of cities benefit from the presence of rats in any way?

Parsons: Historically, during times of famine, humans have used rats as a food source. In some areas, rats are loved and enjoyed, like in a petting zoo. Rats also outcompete and kill mice, a process called muricide. So for those who hate mice, perhaps rats are the lesser of two evils. Rats are sentient, clever, and sometimes affectionate animals. One of the co-authors has adopted one.

RG: Do you have any advice for New Yorkers, or residents of other cities, about living alongside rat populations?

Parsons: 750,000 people pass through Grand Central Station every day; 5.7 million people use the subway. Should we not take every possible precaution to ensure our safety and that of our families, by learning all we can learn about city rats, and by systematically and longitudinally assaying the pathogens of the animals we are—directly or indirectly—continually coming into contact with?

RG: What does the future hold for rodent research?

Parsons: The aim for our study was to overcome a number of logistic barriers, both social and physical, that limit urban rat studies. We have successfully made some progress. We now want to continue the conversation others have started as to whether we should be routinely test rats for the potential pathogens they might carry.

We’re asking public health officials to be proactive and not reactive. The mayor recently spent three million dollars on a new type of garbage bag that hasn’t been scientifically shown to be more effective than the old bags. Why not take a similar level of funding and invest in rat-related research? A better understanding of the animal would likely lead to better control mechanisms anyway.

Featured image courtesy of Javier Valencia Romero.