Rat fight
The term “rat” encompasses 56 known species, but two are more widespread than any other: the black rat (Rattus rattus) and the brown rat or Norway rat (Rattus norvegicus)—both originally native to different regions of Asia and both now invasive worldwide. Through historical records, it’s long been known that black rats were the first to arrive in North America, stowing away on the ships of Columbus and other European colonists to the Caribbean in the 15th Century, and spreading from there. Brown rats showed up in the Americas later, though exactly how much later has gone unresolved.
Many historical accounts indicate an arrival date sometime around U.S. independence in 1776, says Guiry. Yet the new research suggests brown rats were in North America much sooner than that. It can be difficult to accurately date brown rat remains at archaeological sites because the rodents burrow (in contrast, black rats climb), and so more recently living brown rats can end up infiltrating older sites. Plus, radiocarbon dating isn’t particularly precise for things less than 300 years old. But the shipwreck data provides clear proof that brown rats were being carried across the Atlantic by 1760 at the latest. Numerous findings from the terrestrial sites further suggest the species established in North America as early as 1731.
Once here, brown rats rapidly took over black rats’ turf, dominating in just a few decades, per the study.
To distinguish between the historical remains of black and brown rats, the researchers used a molecular analysis protocol called ZooMS that identifies different species based on the amino acid makeup of collagen proteins inside bone. They found that, by the mid-1700s, black rats went from the sole or dominant species in site samples to rare compared to their brown counterparts. Only five black rat specimens were identified from samples after 1760, and just two samples out of 108 showed black rats occuring after 1800. Meanwhile, brown rat samples proliferated over the same time period. The findings provide firm scientific support for anecdotal evidence brown rats had become dominant, outcompeting black rats in most early North American coastal cities by the 1800s. Today, brown rats account for the vast majority of rats in North American cities, with few exceptions