Brown rats hitchhiked to North America in the mid-1700s, triggering a brutal war of the rats that saw a sharp transition from black to brown rat dominance on the continent, a new study finds.
A new analysis suggests brown rats landed on North American soil around 1740 and rapidly pushed black rats out of burgeoning coastal cities. The new invaders may have established dominance by monopolizing food resources, reducing the black rats' reproductive success and gradually shrinking their population.
To retrace brown rats' journey across North America, the researchers examined rodent remains from 32 settlements and seven shipwrecks dating to between 1550 and the 1990s, stretching from the Gulf of Mexico to Canada. The team analyzed bone collagen to identify black and brown rats, as well as different isotopes, or versions, of carbon and nitrogen atoms to reconstruct the rodents' diets.