Lichen is a unique life form, representing a symbiotic relationship between a fungus and a photosynthetic partner, typically an alga or cyanobacterium. This partnership allows the organism to thrive, covering rocks, soil, and trees across the globe. Yes, deer consume lichen, and this behavior is an ecologically significant part of their foraging strategy. The consumption of this dual organism provides deer with a concentrated source of energy when their typical diet is unavailable.
Lichen Consumption During Periods of Scarcity
Deer resort to eating lichen most heavily during the winter months, when preferred browse like leaves, forbs, and tender twigs are scarce or buried under deep snow. This makes lichen a crucial emergency food source, particularly in northern forests and mountainous regions. Consumption is often an opportunistic behavior, where deer take advantage of what is most readily available.
Arboreal lichens, which hang from tree branches, become a primary target in these conditions. Storms and high winds cause “old man’s beard” lichen, such as Usnea and Bryoria species, to fall to the forest floor as litterfall, where deer can easily graze. In some areas, an obvious “browse line” is visible on trees, indicating the maximum height deer can reach to pull the stringy lichen from the lower branches.
The reliance on lichens is especially pronounced in caribou and reindeer, which may rely on terrestrial lichens for up to 90% of their winter diet, often scraping through the snow to find them. While deer do not rely on it as heavily, consumption by white-tailed and mule deer increases significantly during harsher winters when ungulate densities in forested habitats are high.
Nutritional Value and Digestibility
The nutritional value of lichen for deer centers on its high carbohydrate content, which acts as an energy source for surviving the cold. Lichens are composed of a large amount of polysaccharides, including the complex carbohydrates lichenin and isolichenin, which make up a substantial portion of their dry weight. These carbohydrates are highly digestible by ruminants and provide a slow-release energy source, helping deer maintain their body temperature and fat reserves.
Specialized microorganisms within the deer’s four-chambered stomach, or rumen, are adapted to break down these unique lichen polysaccharides effectively. Studies have shown very high dry matter digestibility for some arboreal lichens, exceeding 85%, which is comparable to high-quality forage. However, lichens are generally low in crude protein, often containing less than 7% of the dry matter, which is insufficient for long-term maintenance of a positive nitrogen balance.
Deer cannot survive on lichen alone and must supplement their diet with other browse to acquire sufficient protein and minerals. While lichen can be a source of some trace minerals, its primary function is as a highly concentrated energy ballast. The high digestibility of the carbohydrates, coupled with their availability when other foods are gone, makes lichen a valuable survival ration.
Palatable and Avoided Lichen Species
Deer do not consume all lichen species equally, demonstrating a clear preference based on species-specific chemistry and growth form. The most palatable species are often the arboreal ones that hang from trees, such as the hair-like Bryoria and Usnea species, commonly known as “Old Man’s Beard.” These lichens are readily eaten when they fall to the ground or are within reach.
Terrestrial species, often referred to as “Reindeer Moss” (Cladonia species), are also consumed, though they are more characteristic of caribou and reindeer diets. Preference is influenced by secondary metabolites, which lichens produce for defense. These substances, known as lichen acids, can make a species bitter or toxic.
Deer avoid certain lichens, such as the bright yellow Letharia vulpina (Wolf Lichen) and some Parmelia species, due to the high concentration of these unpalatable or toxic compounds. For example, some lichen acids like usnic acid and atranorin are known to be antibacterial and can be lethal in high doses. This chemical defense mechanism forces deer to be selective, prioritizing high-energy, less chemically defended species during periods of food stress.