Through carbon dating of specimens from packrat nests, scientists can put together a portrait of the prevalence of different plant species in an area over time, similar to the long view obtained by drilling into Arctic ice cores for plant samples trapped there.
“There are twigs and seeds and things in the middens that are easy to work with,” Dr. Cole said. “You don’t have to look at some microscopic piece of leaf. The rats collect some of everything. The nest is like a snapshot of that particular spot at some time in the past.”
Oh, well do I remember Don Grayson's western North American class and the dozens of pack rat midden articles we had to read. . . . .
Fascinating stuff though. See here (scroll down to the "Pack Rat Middens" section) for some links.