How brown rats crawled off ships and conquered North American cities – Orange County Register

By LAURA UNGAR | AP Science Editor

Brown rats are the undisputed winners of the real rat race.

New research suggests they crawled out of ships arriving in North America earlier than previously thought and outcompeted their rodent rivals – something that infuriated and disgusted generations of city dwellers and became so ubiquitous that They are known as common rats, street rats or sewer rats.

It didn’t take long for them to ward off the black rats that had likely arrived with Columbus and were thriving in colonial cities.

After first appearing on the continent before 1740, Norway rats succeeded black rats on the East Coast “within just a few decades,” said Michael Buckley, one of the authors of a study published Wednesday in the journal Science Advances .

Norway rats are larger and more aggressive than roof rats — and they want to be close to human populations, said Matthew Frye, a researcher and community educator at the New York State Integrated Pest Management Program at Cornell University. .

Through this research, “we know the more exact time they arrived and what they were doing once they got here,” said Frye, who was not involved in the study. “Having this picture of the rat population helps us better understand what they are doing and perhaps how we can manage them.”

Neither rat species is native to North America, said Buckley, of the University of Manchester in the United Kingdom. Scientists thought Norway rats arrived around 1776. The new study pushes that date back more than 35 years.

Buckley and his colleagues analyzed rodent bones previously excavated by archaeologists. The remains came from 32 settlements in eastern North America and the Gulf of Mexico, dating from the founding of Jamestown in 1607 until the early 1900s. Other samples came from seven shipwrecks dating from around 1550 to 1770.

The data suggests that shipping networks across the Atlantic Ocean “essentially functioned as rat superhighways,” with brown rats gaining a foothold in early coastal shipping centers, said Ryan Kennedy, an author of the study at the Indiana University that studies animal remains at archaeological sites.

One likely reason for their dominance, researchers say, is that they were eating food that black rats would have otherwise consumed – which may have reduced reproduction among black rats. Historical anecdotes support this discovery, describing the virtual disappearance of black rats from cities in the 1830s.

Today, both types of rats exist in North American cities, although Norway rats are more common. Certain urban centers are particularly invaded. New York City, for example, hired a “rat czar” last year to tackle a growing problem.

The biggest problem ? Rats can carry diseases. Norway rats are known to spread a bacterial disease called leptospirosis, caused by bacteria found in the urine of infected animals. They can also help spread murine typhus and foodborne germs like salmonella.

Experts said knowing which type of rat is leading the pack helps cities control pests, even if it sometimes doesn’t seem like it.

For example, Norway rats like to hang out on or near the ground rather than in trees or other high places, where roof rats often prefer to stay.

Black and brown rats are omnivorous, but Norway rats are particularly fond of animal products, meaning that reducing those present in food waste “should have the greatest chance of reducing the value of urban habitats for rat populations,” Buckley said.

Frye said any efforts to reduce available food waste are helpful.

“Availability of food is the main reason Norway rats are present,” he said. “Any effort to prevent rats from accessing food sources is an effective measure.”


The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Education Media Group. The AP is solely responsible for all content.

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