Hazelnuts, often called filberts, are a concentrated energy source highly desirable in natural ecosystems. Packed with nutrition, including high levels of monounsaturated fats and protein, they are valuable for animals preparing for winter or reproduction. The substantial caloric content provides a significant energy payoff for the effort required to break through the hard shell. This rich resource creates intense competition among different wildlife species, each with unique methods for accessing the valuable kernel inside.
Ground-Dwelling Mammals
Small mammals are the most common consumers of fallen hazelnuts, and their distinct feeding signs can be used for species identification. Squirrels, including gray, red, and flying species, possess the strength and dexterity to split the nut neatly in half along the shell’s seam. Their sharp incisors are specialized for this powerful, precise action, leaving behind two clean, symmetrical pieces.
Smaller rodents like mice and voles employ a different gnawing technique, resulting in a circular or ragged hole. A wood mouse, for instance, leaves tooth marks radiating across the edge of the opening as it works to enlarge the entry point.
The bank vole creates a clean-edged, round hole, but its tooth marks appear only on the rim of the hole, not on the shell’s face. Larger, opportunistic consumers like deer or bears may ingest the nuts whole, but the primary pressure on the nut crop comes from these specialized gnawing animals.
Avian Foragers
Birds contribute to hazelnut consumption using methods that rely on their powerful beaks or external tools. Various species of jays, such as the Blue Jay and Steller’s Jay, harvest nuts directly from the tree, often while the shell is still partially encased in its leafy husk. They use their strong, pointed bills to chip away at the shell.
Woodpeckers and nuthatches employ a specialized foraging behavior known as the “anvil” technique. They wedge the nut tightly into a crevice in the bark of a tree trunk or a fence post, effectively securing the hazelnut like a vice. Once the nut is immobilized, the bird repeatedly strikes it with its bill, using the wedge as a stationary surface to crack the shell and access the inner kernel.
Insect Pests of the Nut
Invertebrates pose a threat to the nut crop while it is still developing on the tree, often targeting the soft shell stage. The filbert weevil is a primary pest that drills a small, precise hole into the young nut using its long snout, or rostrum. It then deposits an egg inside the shell, which hardens around the developing larva.
The resulting grub consumes the entire kernel internally before chewing a clean exit hole to drop to the ground and overwinter. Similarly, the filbertworm, the larva of a moth, enters the nut when the shell is soft, feeding on the kernel and leaving behind frass and mold. These internal pests cause significant damage, often leading to premature nut drop and rendering the kernel inedible for other animals.
The Ecological Outcome of Consumption
The relationship between animals and hazelnuts extends beyond simple consumption to a symbiotic ecological function. Many mammals and corvids, such as jays and squirrels, engage in scatter-hoarding, burying individual nuts in numerous locations for later retrieval. This strategy minimizes the risk of losing an entire food cache to a single competitor.
While these animals have excellent spatial memory, a certain percentage of the buried nuts are inevitably forgotten or misplaced. These unrecovered nuts are left in the soil at an ideal depth and location for germination, effectively acting as planted seeds. This caching behavior is the primary mechanism for long-distance seed dispersal and the successful establishment of new hazelnut plants.