By the time you鈥檝e read this, hundreds of thousands of rats will have been born, destined to colonise our congested cities, spreading disease and economic havoc wherever they go. Why is this so? City life and misguided policies mean today鈥檚 rat is more farm animal than urban nightmare. So who鈥檚 to blame and what鈥檚 the solution? Bruce Colvin ought to know. After studying barn owls and the ecology of small mammals, he鈥檚 been battling America鈥檚 rats for 20 years. New York is just the latest in a string of US cities including Boston and Washington DC, to suffer rat hell. Diane Martindale asked Colvin what he鈥檇 do to stop rats from devouring the Big Apple.
Why should the public be concerned about a rising rat population?
Multiple reasons. First, the presence of rats is an economic issue. They damage utility lines and wires, start fires and damage a lot of a city鈥檚 infrastructure in locations we can鈥檛 observe such as in sewer walls or under sidewalks. Secondly, it鈥檚 a public health concern. Rats roam the sewer systems and carry all kinds of germs. With a higher number of rats our chance of coming into contact with those germs increases. Third, it鈥檚 an aesthetic issue. The presence of rats is a common indicator of a degraded environment. Who wants to live on a street or visit a restaurant where there are rats?
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What makes rats so resilient and hard to control?
Their ability to adapt quickly. Adaptability includes the ability to swim, climb, burrow, and make holes, and their great ability to gnaw and access food, even in containers. At the core of their success is their reproductive ability. They can produce between 8 and 10 pups in a litter every 21 days (rats can have sex up to 20 times a day). If the food is available, the population grows very rapidly. Also, rats have become genetically resistant to some of our poisons, especially the first generation anti-coagulants, which cause internal haemorrhaging. And since rats mistrust anything new, today鈥檚 poisons are designed to take effect between three and five days later.
What preys on rats?
In large cities, it鈥檚 cars, people setting traps and poison, and other rats. Cats can go after rats but usually only the small ones. Between the rats and garbage, the cats will choose the garbage, even the cats don鈥檛 want to deal with them. In urban settings, it has no real predator.
Do rats have any one Achilles鈥� heel?
Food. The mainstay of their diet is our food either before we鈥檝e decided to eat it or after we鈥檝e thrown it away. When the food source is taken away, the potential for a rat problem is no longer going to exist.
What鈥檚 the worst rat problem you鈥檝e ever seen?
It was behind a restaurant in Boston. There was an overflowing dumpster full of rats. There were so many that there was nowhere left for them to live, except in the trash.
Do rats really crawl up toilets?
It鈥檚 true. It usually happens in the basement or first-floor level. Rats only need to swim through about 6 inches of water to get in the bowl and for a rat that鈥檚 a piece of cake. This is probably the most frightening kind of encounter with a rat, especially if you鈥檙e sitting on the toilet.
Should people adopt rats as pets?
Domesticated rats from a pet store are OK, but I wouldn鈥檛 recommend taking one in from the streets. These are wild animals and they will bite. Domesticated rats are very adaptable to being around people and make interesting pets. In college, I had a pet rat named Sheldon. He learned a lot of tricks during the two-and-a-half years I had him. He would come like a dog when I called his name. He also constantly tried to assassinate my goldfish.
Not very friendly. So how did you go from studying the ecology of barn owls to control methods for rats?
As an undergraduate I studied the ecology of small mammals, specifically prey and predator relationships in barn owls. That work drew the attention of William Jackson, a pest ecologist at Bowling Green State University, Ohio, who recruited me to do my doctoral work. It all evolved into applied strategies for controlling rodent populations and doing it in an ecologically sound manner. In my spare time I still do wildlife conservation work on owls with the Barn Owl Research Foundation in New Jersey.
Why does New York City have more of a rat problem today than it did 75 years ago?
Using plastic bags to store garbage and putting bags out overnight for pick-up is one big reason. Second, cities are more congested. More people means more restaurants and snack bars and more refuse, but also less space for trashcans and dumpsters. More people also means more cars which serve as cosy rat motels. Third, the sewer system was built 75 years ago and is now ageing badly. Rats burrow into loose bricks and live on the sewage. Basically, we鈥檙e inadvertently doing wildlife management for the rats as if they were an endangered species. We鈥檙e promoting the growth and reproduction of these animals.
Why haven鈥檛 traditional control methods worked there?
The failure of most cities that depend solely on traps and poison is to do with lack of a long-term vision. They just focus on killing the rats they have today. All you鈥檙e doing is harvesting the standing crop of rodents, and those few that are left have less competition for the food that鈥檚 available and so reproduction rates surge.
Boston, on the other hand, called you to help with the Central Artery Tunnel Project in 1991 because officials feared a huge rat problem. What was your strategy?
This was the largest public works construction project in the history of the US, which involved ripping apart the infrastructure of one of the country鈥檚 oldest cities. We knew that any increase in rats would be blamed on the construction. And we didn鈥檛 want the rats moving from construction areas to neighbourhoods or vice versa, so we even specified how construction workers were to dispose of their food. We mapped all sewer and utilities systems and laid poison, which was tracked using computer mapping. And we worked hard with the city of Boston and with agencies responsible for sanitation regulations. The city ended up being my urban lab for 10 years-it took me from the research side of things into the real world.
What did you find out from that research?
The most important thing I learned is that we have to keep asking and answering the question: why are the rats here? We knew that sewers are reservoirs for rats, but to make our poison baiting efforts more effective we needed to know which sewers rats preferred. So we looked at engineering blueprints and worked out how much of our poison baiting was consumed by rats in the many different sewers. Rats prefer sewers that are less than 24 inches in diameter and made of brick. The older brick sewers are more popular than the modern precast concrete variety. We also put out our poison baits in the reservoirs during late winter and early spring before the seasonal breeding took place. This helped curb the numbers dramatically.
How did you involve local people?
After studying over 50 different landscape plots, we found thick shrubs, trees with low growing branches and needle evergreens to be the rats鈥� favourite habitats. We asked everyone to trim their shrubbery. And we studied the rats鈥� ability to excavate gravel because it is often used as mulch around buildings. Five inches of gravel is enough to keep them from burrowing.
Were you successful?
Surface rat population in Boston was reduced by 98 per cent, so I鈥檇 say it was very successful. The Boston project became the model that鈥檚 been shared with other cities in the US and elsewhere.
When Washington DC was battling the rats in 1999, they also called you in. What did you do?
It is unprecedented when a mayor calls an expert on rat control and gives him access to all city agencies, saying: 鈥淒o what needs to be done for environmental management.鈥� So I toured the city, talked to residents and read the records from public hearings to get a feel for what was going on. I told the mayor he needed to reorganise several city departments in order to develop a comprehensive and sustainable programme to manage the environment. The central idea was that one city agency would be responsible but that several agencies had to participate and cooperate, including ones that collect the garbage, handle sanitation, sewers and urban planning. Then we had to integrate all this with the participation and cooperation of the neighbourhood organisations and businesses. So getting a team approach established is the key foundation to a good programme. It will take around five years to see results.
What would be the ideal rat control programme for New York?
Any city that takes the issue seriously will have to adopt a similar programme to Washington if they want a successful and sustainable one. Alternatively, they could spend a lot of money on poison and function like a farmer growing a hay crop where they harvest off so many rats one season and then they regrow and harvest a bunch more and it continues. It鈥檚 like farming rats in US cities. We need to get out of farming. Being able to walk the political minefield that exists in many cities and explain things in a way that motivates residents and businesses is tricky. Rodent control is an issue that鈥檚 swept under the rug.
Will New York win the rat race?
Winning needs to be defined. It鈥檚 not about expecting a whole city to be rat-free-that鈥檚 possible within a building and even in a city block. But if your perspective is the entire city, the win is to keep the rat population very low. As the keynote speaker a recent rat summit in NYC I summed up the situation as this: people provide the food and the rats provide the sex. That鈥檚 the basic equation. Stop chasing the critters. Manage the environment and the numbers will come down.
Have you fought rat wars outside the US?
I鈥檝e lectured in Argentina, China and the Philippines. In these countries the focus is not on urban problems but on the impact of rats on crops and plantations, and warehouses where rice and other grains are stored.
So what can we all do at home to stem the rising rat population?
A sturdy trashcan with a lid and no holes-and not leaving trash out overnight-would help. Then check outside walls for cracks or breaks and repair them so that rats and mice can鈥檛 get in or out of the building. Make sure food isn鈥檛 left out overnight. People must realise the need to improve the urban environment, whether it鈥檚 their own backyard or whether it鈥檚 municipal.