Walnuts, including the thin-shelled English variety and the dense Black walnut native to North America, are a concentrated source of energy for wildlife. The nutmeats are packed with fats, protein, and essential nutrients, making them a highly sought-after food source. This nutritional reward is protected by a tough shell, requiring animals to possess specialized physical adaptations or clever behavioral strategies to access the contents.
The Primary Mammalian Consumers
Rodents are the most persistent and successful mammalian consumers of walnuts, with squirrels and chipmunks leading the effort. Gray and Fox squirrels, equipped with continuously growing incisors and powerful jaw muscles, access the nutmeat by gnawing through the shell. They often use a methodical approach, holding the nut with their forepaws and creating a small hole or carefully peeling back the shell along its natural seam to avoid shattering the contents.
Immediate consumption is contrasted by scatter-hoarding, where squirrels bury individual walnuts across a large territory for later retrieval. Other species, like the smaller Red squirrel, practice larder-hoarding, storing a large collection of nuts in a single, protected location. This caching activity aids walnut seed dispersal, as many buried nuts are never recovered, allowing the trees to propagate. Secondary consumers, such as mice and rats, usually target nuts that have already been cracked open or gnaw on the exposed nutmeat after the initial husk has been breached.
Avian Strategies for Opening Walnuts
Birds that consume walnuts typically rely on environmental manipulation rather than physical gnawing to overcome the shell. American crows and ravens, members of the intelligent corvid family, are well-known for their inventive techniques. These birds frequently drop walnuts from a considerable height onto hard surfaces, such as rocks or roadways, relying on the impact to fracture the shell.
For the hard Black walnut, the dropping height is often adjusted, with crows selecting greater altitudes to increase the force of impact. In dense urban areas, Carrion crows have been observed placing walnuts directly into traffic lanes and waiting for passing cars to crush them. Other nut-eating birds, including certain woodpeckers and jays, may use “wedging,” jamming a nut into a crevice to hold it steady while they hammer it open with their beaks.
Regional and Occasional Feeders
Beyond the primary consumers, a variety of larger mammals opportunistically feed on walnuts. Raccoons, opportunistic omnivores with strong jaws and dexterous front paws, consume walnuts they find on the forest floor. They may employ a technique similar to the crow’s, using rocks or other hard objects to assist in cracking the shell.
In forested areas of North America, black bears forage for walnuts, especially during the fall as they seek to build up fat reserves for hibernation. While bears possess the crushing power to deal with the shell, walnuts are a minor component of their seasonal diet. Deer are also occasional feeders, though they are more likely to consume the tender leaves, twigs, and young shoots of the walnut tree rather than the nutmeat.