Bone gnawing in a Japanese squirrel

Abstract

Well-known for consuming tree nuts, seeds, and fruits, squirrels occasionally eat other types of food, including fungi, lichens, and tree bark, especially when their main food sources are scarce. Squirrels adapt their diet to conform to changes in food availability through seasons and across environments. Interestingly, we observed several individuals of the Japanese squirrel (Sciurus lis) gnawing on the jawbones of sika deer (Cervus nippon) in Chino City, Nagano Prefecture, Japan.

Why would squirrels gnaw bones? The key to unraveling this mystery may lie in the fact that most individuals gnawing bones are lactating mother squirrels. In combination with anecdotal reports documenting bone consumption by pregnant and lactating eastern gray squirrels (Sciurus carolinensis) (Science 1940; doi.org/10.1126/science.91.2372.573.b), bone gnawing probably provides squirrels, especially lactating mothers, with important minerals such as calcium and phosphorus. Due to the energetic demands associated with reproduction and milk production, female squirrels have increased mineral requirements during breeding and lactation. It would be worth investigating whether bone consumption increases the reproductive fitness of squirrels.