The sight of a squirrel, known for its diet of nuts and seeds, gnawing on a bone might seem unexpected. These residents are more than just nut hoarders, exhibiting a flexible diet that sometimes includes animal matter. While their usual forage is rich in fats and proteins, it often lacks certain inorganic materials necessary for survival. This nutritional gap drives a surprising behavior, linking the rodent to the decomposition cycle in the pursuit of a balanced diet.
The Direct Answer: Why Squirrels Engage in Osteophagia
Squirrels intentionally seek out and consume bones to supplement their nutrient intake. This dietary behavior is known as osteophagia, or “bone eating.” The primary motivation is a deficiency of certain salts and minerals in their staple diet of seeds, nuts, and vegetation. This deficiency is particularly noticeable during late winter and early spring when natural food resources are scarce.
Their typical diet, especially nuts, is high in phosphorus but low in calcium. This imbalance creates a physiological need for the missing elements. Consuming bone material is a direct response to a mineral deficit, acting as a necessary survival mechanism.
Essential Minerals Derived from Bone
The two elements squirrels seek from bone material are calcium and phosphorus, which are abundant in vertebrate skeletal structures. Calcium is an important component for maintaining strong bone structure and plays a regulatory role in muscle contraction and nerve signaling. This mineral is particularly important for female squirrels during gestation and lactation, as producing milk rapidly depletes their body’s calcium stores.
Phosphorus, while often present in their regular diet, is needed in a specific ratio with calcium for optimal absorption, ideally around 2:1 (calcium to phosphorus). A diet dominated by seeds throws this ratio out of balance, risking a condition called Metabolic Bone Disease (MBD). By gnawing on bones, the squirrels effectively restore this balance, which is necessary for proper energy transfer and cell repair.
Behavioral Context and Sources of Bone Material
Osteophagia involves a focused gnawing motion that leaves grooves on the bone surface. This act serves a dual purpose, addressing both nutritional and mechanical needs. Gnawing on hard materials is necessary to wear down the squirrel’s four incisors, which grow continuously. Without this grinding, their teeth could grow too long, leading to malocclusion that would prevent them from eating.
In the wild, primary mineral sources come from shed deer antlers, which are rich in calcium and phosphorus, and the dried remains of animal carcasses. Squirrels are often observed transporting these items, sometimes dragging a bone up a tree for a secure feeding location. This behavior is seen more frequently in areas where the soil and local vegetation are naturally low in these minerals.