This guide is about Rattus norvegicus
; the "Norway Rat", "Street Rat", "Sewer Rat" or "Brown Rat". You've probably seen them in pet stores under the handle of "Fancy Rat", and in laboratories across america, an albino variant of them is often called a "Lab Rat".
Although they are technically the same species, the behavior of a Norway rat in a New York alleyway is a lot different than the behavior of a Norway rat you'd buy in a pet store, or a rat out in the woods. I used to work in a pet store, and I can assure you that pet store rats are some of the friendliest, most docile, most loving pets you can find.
However, this guide is not about pet store rats. It's about rats as they act and behave and live on the streets. It's about city rats.
In particular, most of this information comes from Robert Sullivan, who spent an entire year in an alley watching wild city rats in an infested alley in New York. When I ran into conflicts between his accounts and other sources, I tended to favor his accounts, as they were specific to city rats in particular, while other sources spoke of rats in pet settings or in general.
Overview and General Biology:
Rats live wherever human beings live. The live on our garbage, mostly hidden from our sight. Because they are so shy and determined to be hidden, a common rule of thumb that exterminators use is that "for every rat you see, there are at least ten you don't".
They are stocky in build, and average to be a little under a foot and a half long from their nose to the tips of their tails, and usually weigh about a pound. However, in areas where food is plentiful and rats can live long lives, it's not unheard of for them to be found at much larger sizes; over two feet long and over two and a half pounds. (Go ahead, get a ruler and measure two feet long. Now picture a rat that big. Yeah.) Males are usually bigger than females
Rats are most active at night time; to see a rat during the day is a sign of a SERIOUS infestation. About the only time a rat will come out during the daylight is when they are so numerous that it was not able to compete with the night-time foragers. A rat out in the day time is like you going to the grocery store at 3 am because the parking lot is too full the rest of the time.
Although rats have very poor eyesight (About 20/600 and red-colorblind), they have an excellent sense of smell and taste, and can detect poison down to one part per million. To compare this to human ability, we can only smell rotten eggs--to us a very strong odor--at 30 parts per million.
Their ability to run and climb is almost squirrel-like, but unless specifically going after a food source, they generally will not climb due to their poor vision. When a rat decides to run, it is not a skittering or crawling motion--it's a full-on gallop that can reach speeds of 24 mph for short bursts. They are also incredibly strong swimmers, and often will swim through even the nastiest sewer water with no ill effects on their health.
Their teeth are yellow, and the incisors grow at a constant rate; rats must gnaw to wear them down. However, it has been found that rats will gnaw even when their teeth are not in need of "trimming". The strength of a rat's teeth is comparable to steel, with a biting force of 7,000 pounds per square inch. (To compare: a wolf's bite is only about 1,500 pounds per square inch, a human only about 120)
They can (and often do) gnaw through concrete, aluminum, copper, lead, and iron. Rats and mice are for some reason particularly attracted to wires and cables.
Along with gnawing, rats love to dig and tunnel. They often nest under sidewalks, as described by Robert Sullivan in his book, Rats
[quote author=Robert Sullivan]Entrance to a typical under-the-sidewalk rat's nest is gained through a two-inch-wide hole--their skeletons collapse and they can squeeze into a hole as small as three quarters of an inch wide, the average width of their skull. This tunnel then travels about a foot down to where it widens into a nest or den. The den is lined with soft debris, often shredded plastic garbage or shopping bags, but sometimes even grasses or plants; some rat nests have been found stuffed with the shavings of the wood-based, spring-loaded snap-traps that are used in attempts to kill them. The back of the den then narrows into a long tunnel that opens up on another hole back on the street. This second hole is typically called a bolt hole; it is an emergency exit. A bolt hole is typically covered lightly with dirt or trash--camouflage. Sometimes there are networks of burrows, which can stretch beneath a few concrete squares of sidewalk, or a number of backyards, or even an entire city block.
Rats can also nest in basements, sewers, manholes, abandoned pipes of any kind, floorboards, or any hole or depression.[/quote]
Rats are thigmophilic, or touch-loving, and prefer to be in contact with something at all times. Due to their poor vision, they are dependent on their sense of smell and their sense of touch to navigate the world. They tend to travel along curbs, parallel to walls, and along pipes. They are also particularly fond of corners.
The color varieties of tamed Norway rats are very numerous, and are a subject for their own guide. However, wild and sewer rats generally come in one variety: Brown, with yellow or white bellies.
Foraging and Diet:Foraging:
When moving to a food source (typically a dumpster), rats tend to stick close to the walls, and move in sudden bursts with long, careful pauses to survey their surroundings. Older rats get first claim on food sources closer to the nests, so smaller, weaker rats are forced to search farther away from their safe holes when foraging.
Once they get to the trash bag they want, larger rats will typically just rip a hole and go right in, retrieve a tidbit it wants, then come out to eat it. Smaller, lower-ranked rats, however, generally wait patiently outside the bag, eating at the bits of food the larger ones invariably kick out as they enter and leave the bags (whether intentionally or not).
Sometimes a rat will sit right by the bag to eat it's food, and other times it will take the food back to it's nest to eat. Which it does is generally based on two main factors: how safe it feels, and whether or not there are pups back at the nest to be fed. If it's feeding pups, it will take food back for them to eat. If it feels unsafe or threatened, it will also return to the safety of the nest to eat.
But if it has no hungry pups, and feels good and safe right where it is, a rat will sit right there and chow down.
When presented with a new food source, no matter how tempting, rats will almost always stick with their old food source until it runs out. You could offer a rat chicken coated in peanut butter, and it would still keep eating the cardboard it had been eating before, because the cardboard is familiar. This natural neophobia can make poisoning rats quite difficult.Diet:
Rats require two ounces of water a day, but it need not be fresh, or even clean. They will either scoop up bits of it to drink with their paws, or lap it up by dipping their noses in.
As for food, rats eat what people eat. In fact, it is estimated that rats destroy about 1/3 of all food produced world wide, and that's not counting the fact that they eat our leftovers, too.
In the city streets and alleyways, rats thrive on garbage. About a third of what we throw out is edible to rats--even moreso for restaurant garbage. It's been said that every major rat infestation requires one really good chicken restaurant. Chicken is an absolute favorite of rats, though they are often said to be fond of peanut butter.
Rats are incredibly neophobic, and view anything new in their environment with a great deal of suspicion, which makes them incredibly difficult to catch using conventional traps.
They live in colonies with a strict pecking order, usually with one incredibly large dominant male. He gets the best burrows, mates with the most females, and eats the best food. Likewise, large females tend to get better nesting sites than smaller females, and have larger, healthier litters.
Subordinate rats have two main strategies in dealing with dominant rats--either they avoid the dominant ones, or they stay quite close. Rats that stay close to the dominant rat tend to show more submissive behaviors, and are better-tolerated. Rats that avoid them, however, tend to be on the brunt end of more aggression on the rare occasions that they encounter the dominant rats.
When food supplies run short or rats overpopulate, it's the small rats that go hungry first, while larger ones remain well fed. If food runs so low that even the big rats get hungry, they'll start to cannibalize the small rats.
Despite this pick-on-the-little-guy mentality, rats very rarely leave the colony they are born in to. Studies with tracking the movements of city rats have revealed that typically rats will never travel father than 65 feet away from the nest they were born in (males will occasionally roam a little farther than this, females very rarely roam even that far).
If something happens that reduces the population of a colony suddenly (trapping, poisoning, a flood, whatever), the reproductive rate of the rats left behind doubles, and their size and weight greatly increases. The rats that survive any catastrophe become quite strong, and those that died off only made room for the survivor's offspring to thrive.Fighting:
Rats are extremely territorial, and will drive off rats from other colonies that attempt to nest in their spot or eat their garbage. Likewise, a few big rats will think nothing of taking down an intruding dog or cat. Although attacks on humans are rare, there have been a few documented cases of this occurring.
Most rat-on-rat encounters do not result in all-out fights. Usually the smaller rat will either flee, or roll over, exposing it's belly in submission. If it doesn't the rats will stand up on their hide legs and shove and box at each other with their front paws, each attempting to knock the other one down.
If this continues, the rats may escalate further, and lock into a fighting ball. The general goal is to try and sink their fangs into the other rat's rump.
It should be noted that females rarely get into fights with other rats, and males are extremely hesitant to bite a female. Likewise, Juvenile rats are almost never attacked for any reason.
Also, young males will play-fight with each other frequently from about 5 weeks of age until about 6 months. After this age, play fighting drops off and conflicts become much more serious.
Vocalizations and Body Language:Vocalizations:
Here is an excellent site with lots and lots of rat vocalizations, and the context they are heard in:http://www.ratbehavior.org/norway_rat_vocalizations.htmBody Language:
A rat on the defensive will emit loud squeaks and hisses, opening it's mouth to show it's teeth. It's fur will stand on end, and it's tail will lash.
To threaten off an intruder, a rat will stand on it's hind legs, hop forward, and hiss--basically the equivalent of saying "I'm big and I'm mean so back off!"
Rats breed like, well, rats, and are extremely promiscuous. Dominant males breed more than subordinate males; one large male can father over two dozen litters in the space of six hours.
21 days after breeding, the female will give birth to 8 to 10 pups. (She is able to get pregnant again immediately after giving birth). If no male is around for her to breed with (unlikely), she will go into a heat cycle every 4 to 6 days until she becomes pregnant again.Growth Rate:At birth:
Hairless, eyes closed, deaf, no teeth.8 days:
Incisors grow (they're white at this point)9 days:
Fur grows12 days:
Eyes open, ear canals open. Can now see and hear.14 days:
First time leaving the nest for brief periods.19 days:
The rest of the teeth start to come in21 days:
Males are able to breed at 39-47 days of age, while females are ready at 34-38 days.