Q: My backyard soil is so rocky that I often need a pickax to dig a hole, yet chipmunks and moles burrow through with apparent ease. How do they do it?
A: Some burrowing mammals have special bones and other structures for moving earth, and some, notably chipmunks, may reuse tunnels cut by others.
In fact, most burrowers choose their habitat for its favorable soil conditions and appear to time their excavations for periods when digging may be easier, like after rain.
The familiar eastern mole, Scalopus aquaticus, digs two kinds of tunnels. The ones often seen near the surface are used for hunting subterranean foods like insects and grubs. Deeper tunnels, perhaps 12 inches down, are to counter seasonal temperature fluctuations and are used for shelter and hunting.
Moles use a digging technique called sand swimming in loose, sandy soil, but they also have the equipment for heavy lifting and shifting in rocky, root-clogged soil.
An overview of burrowing animals in a chapter of the book Current Mammalogy (Plenum, 1990) discusses some of the adaptations involved, including especially powerful humerus bones in the forelegs; quick-growing front claws that are laterally compressed and strengthened with bony extensions; and a hardened, padded structure on the head to help push past obstacles.
ActiveStyle on 07/28/2014