The Hoh Rainforest, located within Olympic National Park in Washington State, is a unique temperate rainforest. It receives an average of 140 to 170 inches of rain annually, sustaining a massive biomass. This moisture results in a dense, multi-layered forest dominated by towering Sitka Spruce and Western Hemlock trees. Nearly every surface is draped in mosses and ferns, creating a specialized habitat for the fauna. The animals inhabiting the Hoh have adapted to this saturated, old-growth environment, establishing a food web from the river valley floor to the highest canopy.
Large Mammals and Forest Floor Dwellers
The most visible large mammal is the Roosevelt Elk, the largest subspecies of elk in North America. Adult bulls can weigh up to 1,100 pounds. They move through the rainforest in herds, consisting primarily of cows and calves. These non-migratory elk subsist on the lush understory, feeding on ferns, shrubs, and lichens year-round. Their grazing habits shape the forest floor, preventing the undergrowth from becoming too dense and influencing the distribution of other plant species.
The Olympic Black Bear is the only bear species found in the park. These bears are omnivorous, with a diet that includes berries, roots, and fish, and they aid in seed dispersal. Unlike true hibernators, Black Bears enter a state of “carnivore lethargy” during the coldest months, though they can still be active.
The Cougar, or mountain lion, is the apex predator of the Hoh ecosystem, primarily preying on elk and deer. This secretive cat is rarely seen, preferring to stalk prey in dense cover. Smaller inhabitants of the forest floor include the River Otter, which is common along the Hoh River where it hunts fish and amphibians. The Pacific Shrew, a tiny insectivore, relies on the moist environment and decaying logs to hunt slugs, snails, and other invertebrates.
Avian and Arboreal Species of the Canopy
The multi-layered canopy creates a separate habitat zone for arboreal and avian life. The Northern Spotted Owl prefers structurally complex old-growth stands for nesting and roosting, often utilizing large cavities in decaying trees.
The owl’s primary prey is the Northern Flying Squirrel, a strictly nocturnal mammal that glides between trees using a patagium. These squirrels den in tree cavities and subsist largely on fungi and lichens. By consuming truffles, the flying squirrel disperses fungal spores, which is important for forest health.
Woodpeckers, such as the Pileated and Hairy Woodpecker, excavate insects from dead wood. The cavities they create are later adopted as nests and dens by other canopy-dwelling mammals. The Pacific Pine Marten, a member of the weasel family, is an elusive semi-arboreal mammal. Martens are agile hunters that prefer well-established forests and prey on small mammals and birds.
Amphibians and Invertebrate Specialists
The constant humidity makes the Hoh Rainforest an ideal environment for moisture-dependent life, especially amphibians. The Olympic Torrent Salamander is a specialized species endemic to the Olympic Peninsula. It thrives in cold, clear mountain streams and seepages, rarely found far from running water.
The Pacific Tree Frog is a common amphibian, recognizable by its small size and the distinctive dark stripe through its eye. Despite its name, this frog is typically found on the ground or in low vegetation. Other salamander species, such as the Western Red-Backed Salamander, are abundant, living beneath moss and logs.
The most conspicuous invertebrate is the Banana Slug, one of the largest slug species in the world, reaching lengths of up to 10 inches. The slug is an important detritivore, playing a significant role in decomposition by consuming dead organic matter. This process recycles waste that fertilizes the soil and disperses plant and fungal spores.