Ken Baker, Columnist Published 12:27 p.m. ET Jan. 14, 2020

Ken Baker and Cocoa(Photo: Submitted)

According to the Chinese Calendar, the 13 months from Jan.25, 2020, through Feb.21, 2021 will be the Year of the Ratthe Gold Rat.

Each of the 12 Chinese Zodiac signs (rat, ox, tiger, rabbit, dragon, snake, horse, goat, monkey, rooster, dog and pig) is associated with one of five elements: water, wood, fire, earth or metal (gold). So all told, it takes 60 years (12 x 5) to cycle through all possible combinations.

A person born under the sign of the Rat is purported to be quick-witted and resourceful, with a rich imagination though, perhaps, a bit shy in courage. Since Chinese culture attributes diligence and thriftiness to the rat, its expected those born in a Rat year will do pretty well for themselves.

Or so its said.

Setting aside such cultural personifications along with any aversion we might harbor towards the animal, what have we learned about the rats biology and the way it actually lives its life?

In our area and indeed throughout North America and Europe, the species youd be most likely to encounter today is the brown or Norway rat (Rattus norvegicus). But thats only been the case over the last several centuries.

The black rat (Rattus rattus), also known as the roof or ship rat, is thought to have invaded Europe from Southeast Asia sometime between the 4th and 2nd century BC and North America in the 16th century. The somewhat larger and more aggressive Norway rat appears to have reached Europe as stowaways on trading ships from Northern China during the 1500s and North American shores some 200 years later.

In cooler northern climates, the Norway has largely replaced the once abundant black rat, which is still the more common species in tropical areas.

The Chinese Zodiac calendar celebrates 2020 as the Year of the Rat, which gives recognition to this Norway rat.(Photo: Submitted)

It should be noted that there are many other species of larger-than-a-mouse rodents commonly referred to as rats. The genus Rattus alone has over 50 such species and there are interesting beasts called rats in several unrelated genera (Neotoma, Dipodomys and Bandicota, for example).

But the black and Norway are the two species that have played the largest role in human history. In fact to ask about the natural habitat of either mammal poses an interesting challenge. Both have been so closely associated with human habitations for so long that the best description of their normal habitat in nature might simply be wherever people live.

Which is not to say their biology is any less complex and interesting. Female Norway rats, for example, commonly live in colonies of six or so related individuals. Each female will have her own nest chamber within a shared (often underground) burrow. Intriguingly, members of the group will often nurse their young collectively.

While daughters commonly remain with the colony, males disperse soon after being weaned. If the population of rats in the area is relatively low, one adult male will typically dominate the colony, vigorously defending it against other males and mating with its females.

In dense populations, however, there will be too many intruders for him to maintain exclusive control of the colony and he will have to suffer the presence of other males seeking to mate with females when they come into breeding condition (about once every 4 -5 days if not impregnated).

In the wild (that is excluding rats kept as pets or in a scientific laboratory), the average lifespan of a Norway rat is probably less than one year. Studies of several European populations found about 95 percentannual mortality, with just a (very) few venerable old-timers making it to three years.

The rats perception of the world (its mvelt in the language of behavioral biologists) is very different from our own. Their eyesight is quite weak beyond a foot away, they can only detect large shapes and movement and, like most other mammals, they cannot detect the color red.

But this doesnt make them less effective in navigating their environment. Norway rats, which are primarily active at night, live in a world of textures, sounds and smells. When moving about, the Norways long whiskers whisk back and forth several dozen times per second, lightly touching all nearby objects.

They can hear (and communicate with) sounds much higher in pitch than we can detect, and its been estimated that over 1 percentof their genetic material is devoted to the detection of odors.

Finally a word on the connection between rats and the Bubonic Plague that swept through the Eastern Hemisphere in the mid-1300s, killing 25 to 60 percentof the human population of Europe. The so-called Black Death, caused by the bite of a flea carrying the Yersinia pestis bacterium, has long been blamed on the spread of flea-infested black rats.

However more recent studies have strongly suggested Yersinias initial invasion of Europe might be better pinned on gerbils, of all things, which unlike rats can carry the bacteria in their blood for some time without killing them.

Oh, and regardless of its name, the Norway rat has no special association with Scandinavia.

Ken Baker is a retired professor of biology and environmental studies. If you have a natural history topic you would like Dr. Baker to consider for an upcoming column, please email your idea to fre-newsdesk@gannett.com.

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Ken Baker: 2020 is the Year of the Rat, but what do we know about the rodents? - The News-Messenger

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