https://phys.org/news/2018-06-pacific-rats-years-human-impact.html

Ancient human impacts are often difficult to identify and measure compared to those happening today or in recent history. A new study published in the Proceedings of the National Academy of Sciences by researchers at the Max Planck Institute for the Science of Human History in Jena and the University of California, Berkeley advances a new method for detecting and quantifying human transformations of local ecosystems in the past. Using state of the art methods, researchers searched for clues about past human modifications of island ecosystems from an unusual source—the bones of long-dead rats recovered from archaeological sites.

One of the most ambitious and widespread migrations in human history began c. 3000 years ago, as people began voyaging across the Pacific Ocean—beyond the visible horizon—in search of new islands. By around 1000 years ago, people had reached even the most remote shores in the Pacific, including the boundaries of the Polynesian region: the islands of Hawai'i, Rapa Nui (Easter Island) and Aotearoa (New Zealand). Not knowing what they would encounter in these new lands, early voyagers brought with them a range of familiar plants and animals, including crops such as taro, breadfruit, and yams, and animals including the pig, dog, and chicken. Amongst the new arrivals was also the Pacific rat (Rattus exulans), which was carried to almost every Polynesian island on these early voyages, perhaps intentionally as food, or equally likely, as a hidden "stowaway" aboard long-distance voyaging canoes.