Rat waste pile

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Ice Age rat heap

The analysis of the rat waste heaps ( English pack rat midden ) of the American bush rats serves the reconstruction of the environmental and climate development ( paleecology , paleoclimatology ) of the desert areas of the southwest of the USA and Mexico .

Character of the bush rat

The American bush rats (English: pack rats ) belong to the genus Neotoma and show a conspicuous collecting instinct for material of all kinds, which they collect from a radius of less than 100 meters to build nests in caves or crevices: small stones, sticks, twigs, parts of plants, Seeds, bones, snail shells and the like. The abundant urine released by the bush rats - they cover their high fluid requirements mainly by consuming succulents  - penetrates and envelops the diverse nest material and crystallizes into a rock-hard, brownish mass that also contains leftover food, feces, skin remains, insects, pollen, spores and so on and preserved. This scrap heap of the bush rat piles up until the rats look for a new nest after a few decades. With protection against mechanical destruction, sun and moisture, special time capsules or climate archives are created that can be over 40,000 years old (measured with the C14 method ).

Archaeobotanists can identify the remains of several dozen plant species from a rat heap and thus have a snapshot of the vegetation around the building at the time it was used. The remains of vertebrates and insects that have been found allow archaeozoologists to draw conclusions about the fauna of that time.

Results of the rat waste pile analysis

The results of the first rat heap analyzes resulted in a complete overturning of the paleoecological history of America's Southwest. The assumption that the desert landscapes were formed a long time ago, which the European settlers found, was no longer tenable. Specifically, it was shown that the rise and fall of the Anasazi in the Chaco Canyon in the period from 600 to 1200 AD was essentially related to the deforestation of the pine and juniper forest of that time .

The rat waste heap analysis is now a widely used tool for the reconstruction of historical environmental conditions and climate development by determining the “frozen” species composition. The determined data and facts are collected in a central archive of the US Department of the Interior ( North American Packrat Midden Database ) and they are widely used scientifically.


  • Diamond Jared: Collapse - Why Societies Survive or Fall . S. Fischer, Frankfurt 2005, ISBN 978-3-10-013904-7 .
  • Julio Betancourt, Thomas van Devender, Paul Martin: Packrat Middens, The Last 40,000 Years of Biotic Change . University of Arizona Press, Tucson 1990, ISBN 0-8165-1115-2 .

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