The hippopotamus, one of Africa’s largest land animals, spends its days partially submerged in rivers and lakes, earning it the Greek name meaning “river horse.” These massive semi-aquatic mammals possess a tail, though it is strikingly small compared to their enormous, barrel-shaped bodies. The tail is an active anatomical tool that plays a specialized role in their behavior. Its function is directly tied to the social and territorial needs of the species.
The Tail’s Physical Characteristics
The tail of the common hippopotamus is short, typically measuring 13.75 to 19.75 inches (35 to 50 cm) long. It is thick at the base, tapers toward the tip, and is endowed with strong musculature designed for rapid, forceful movement. Unlike the hippo’s nearly hairless body, the tail often retains a sparse brush of stiff, short hairs near its end. Internally, the coccygeal vertebrae feature robust, elongated transverse processes. This bone structure provides a solid framework to anchor the powerful caudal muscles, supporting the energetic actions the tail performs.
Primary Function Territory Marking
The primary purpose of the hippo’s tail is territory marking, which defines boundaries within their crowded aquatic habitats. When a hippo defecates, it rapidly swishes its short, muscular tail from side to side, acting as a high-speed propeller. This vigorous action scatters feces and urine over a wide area, creating a “dung shower” that broadcasts the hippo’s presence and ownership. This practice, often called “dung spreading,” is primarily performed by territorial males to warn off rivals and communicate their status. The chemical signature within the dung acts as a potent signal that other hippos can recognize. The territorial bull often performs this ritual while exiting the water or along established paths, ensuring the scent is spread across their domain. The act of spreading waste is also used during social interactions as a non-verbal display of aggression or dominance.
Other Key Adaptations for Aquatic Life
The hippo’s physiology reflects its semi-aquatic existence. The placement of its sensory organs allows it to monitor its surroundings while largely submerged. Its eyes, ears, and nostrils are located high on the dome of the head, allowing the hippo to see, hear, and breathe with only a small portion of its body above the waterline. The skin requires constant moisture to prevent dehydration. Lacking sweat glands, the hippo secretes a reddish-orange fluid sometimes called “blood sweat,” which acts as a natural sunblock and antiseptic. This fluid protects its sensitive skin from the African sun when it is out of the water. Despite their massive size, hippos are not buoyant. Their high bone density and low center of gravity cause them to sink, allowing them to walk or “gallop” along the bottom of the riverbed. This ability, combined with the capacity to hold their breath for five minutes or more, enables them to spend nearly all daylight hours safely submerged.