Sloths are famously known as the slow-moving, quiet inhabitants of the Central and South American rainforest canopy. This stillness leads many to assume these arboreal mammals are completely silent. However, sloths are not mute creatures. They possess a distinct, though infrequent, repertoire of vocalizations used for specific communication needs within their dense jungle homes.
Sloth Vocalizations: The Primary Sounds
The sounds sloths produce are highly specialized. The most recognizable vocalization is a high-pitched call, often described as a bleat, whistle, or a shrill eeeh sound. This piercing call is particularly associated with three-toed sloths (Bradypus). The sound is loud enough to travel through the thick vegetation, allowing for communication over a distance.
Baby sloths are notably more vocal than adults, relying on sound to signal their needs to their mothers. Infants emit high-pitched cries and squeaks when distressed or seeking attention. Adult sloths, when threatened, may produce a low hiss or a soft grunt as a defensive warning. Two-toed sloths (Choloepus) tend to rely less on vocalizations for locating mates compared to their three-toed relatives.
Communication Contexts
Sloth vocalizations are reserved for moments revolving around reproduction and survival. The loudest sound is the female three-toed sloth’s mating call, which zoologists have described as a “scream.” When ready to breed, the female climbs high into the canopy and emits a series of loud, drawn-out calls to advertise her availability to males. This screaming can occur every 10 to 15 minutes for several days, effectively broadcasting her reproductive status.
The sound acts as a beacon, guiding potential male partners through the trees. Once males arrive, the situation can escalate into a territorial dispute, involving low growls and hisses from the competing individuals. A defeated male may signal his loss with a high-pitched cry similar to the female’s estrus call. This use of sound is essential for bringing solitary animals together in a vast environment.
Why Sloths Are Considered Silent
The perception that sloths are silent comes from the infrequency and context of their vocalizations. Sloths prioritize stealth over sound, a survival strategy tied to their slow metabolism. Moving quietly through the high canopy helps them avoid detection by predators like jaguars and harpy eagles, which hunt by sight and sound. Loud vocalizations would immediately break their camouflage and attract unwanted attention.
Their arboreal habitat further contributes to their perceived silence, as most human observation occurs far below their typical resting height. Sloths conserve energy by minimizing movement and noise, reserving vocal effort for pressing needs like mating or distress. Two-toed sloths minimize vocal announcements of reproductive status by using scent marking—rubbing anal glands on branches—instead of sound. Their quiet demeanor is an adaptation for a successful, energy-efficient existence in the rainforest.