Midden
A packrat midden is a debris pile constructed by a woodrat. A packrat midden may preserve the materials incorporated into it for up to 50,000 years. The middens may thus be analyzed to reconstruct their original environment, and comparisons between middens allow a record of vegetative and climate change to be built. Examinations and comparisons of pack rat middens have largely supplanted pollen records as a method of study in the regions where they are available.
In the absence of rock crevices or caves, the dens are often built under trees or bushes. The packrats will also use plant fragments, animal dung and small rocks in building the den. The vast majority of the materials will be from a radius of several dozen yards of the nest. Woodrats often urinate on the debris piles; sugar and other substances in the urine crystallize as it dries out, creating a material known as amberat, which under some conditions can cement the midden together. The resilience of the middens is aided by three factors. The crystallized urine dramatically slows the decay of the materials in the midden; the dry climate of the American Southwest further slows the decay; and middens that are protected from the elements under rock overhangs or in caves survive longer.
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