Ladies get it on in the daytime, but fellas make their moves at night, discovered researchers at Hofstra University in Hempstead, New York.
The researchers learned this via a new technique they'd developed to gain insight into the lives of New York City's most secretive residents: its rats.
Until now, studying rats in the concrete jungle has been difficult. First you have to find a rat. Despite pizza rat's famed presence in New York City's subway, genus Rattus are surprisingly bashful creatures. Then you have to capture it and take specimen samples—hair, saliva, a bit of blood—without being bitten or scratched. You also need to affix a tracker—one small enough to fit on the back of Mrs. Frisby but strong enough to maintain a signal as she scurries about underground through layers of reception deadening metal and concrete. And then, eventually you have to find and recapture her.
And yet, researchers have found a way to simplify the process.
When we started the project," said Michael Parsons, lead author of the study, published Thursday in Frontiers in Public Health. "it probably took two and a half hours. By the end we got it down to an art—we were at almost 12 minutes per rat."
Parson's and his team use traps baited with pheromones—not food—to capture the rats. They know where to place the traps because rats frequently navigate the dark tunnels where they live not with their eyes, but with their fur. Rubbing themselves against walls creates a trail that's visible with an ultraviolet dark light. According to the study the trail glows blue–white if it's fresh, yellow–white if old. The trap has a sensor attached to it that alerts the researcher by cell phone when a rat has been caught.
Once a rat has been caught, a mobile lab is deployed. Inside researchers wearing thick gloves render the rat unconscious by dipping the rat trap in a plastic induction container filled with isoflurane, a kind of ether. An unconscious rat is an easy rat to draw specimens from. Before it wakes up, the rat blood is drawn and an RFID chip is implanted.
Earlier this year, New York City shelled out $5.6 million to buy mint scented garbage bags to deter rats
When they aren't capturing rats, the bait sits on top of a scale so when the rat returns it can record the weight. Video cameras set-up nearby allow the researchers to study rat behavior.
"They have interesting personalities," said Parsons. 'We have one rat, that we call Stumpy. He became so habituated to our presence that when we were lowering his trap into the induction chamber for the anesthesiology he just sat and groomed himself all the way down. There was just no fear whatsoever."
If this seems like an awful lot of work just to learn about rats, it isn't. According to the study, New York City has between 2 million and 32 million rats, a number which at its upper range would mean that the city's rat population is four times larger than its human population.
The range is so big, in part, because little is known about how urban rats spend their time. This is a problem because rats can carry a host of diseases including leptospirosis, which can cause liver failure, foot and mouth disease, tuberculosis, and perhaps most famously, the Black Death.
They can even carry diseases that we're unaware of—in 2014 researchers studied a sample of 133 New York City rats and discovered 18 pathogens that were previously unknown to science. And a combination of climate change and increased urbanization means that not only will there be more rats than ever, we're more likely to come into contact with them.
"Prior to the earlier 1990s, people who were animal behaviorists really stayed out of working in the urban environment, because animals and people were interacting," said Parsons. They thought that animals had to be studied in their natural environment and people weren't natural. Since the early part of the 21st century, however, there's growing awareness of the need to study animals in conjunction with people.
"Using lab rats to base wild rat knowledge on," said Parsons, "is a little like using the domestic chihuahua to base our studies on the wolf in the wild."
He hopes that his research will get science out of the academy and into the broader world, where it can be used to help control rat populations.
Earlier this year, New York City shelled out $5.6 million to buy mint scented garbage bags to deter rats. "But there's no scientific evidence to say that it works," said Parsons. A better use of those dollars, according to Parsons, would be to "create better attractants and learn what deters them."