--- title: "Proboscis Monkey (Nasalis larvatus) | AnimalTracks.wiki" description: "An oversized nose that works as both a visual badge and a vocal amplifier, webbed fingers and toes that help it swim across rivers, and a cow-like habit of bringing food back up to chew it again." image: "https://animaltracks.wiki/images/animals/proboscis-monkey-1.webp" published: "2026-09-01" updated: "2026-09-16" --- # Proboscis Monkey (*Nasalis larvatus*) > **Status**: Checked against 8 sources, listed under Sources below. > **Tagline**: An oversized nose that works as both a visual badge and a vocal amplifier, webbed fingers and toes that help it swim across rivers, and a cow-like habit of bringing food back up to chew it again. > **Soundtrack Vibe**: Jazz-Funk, Soul & Lounge Fusion // Les Baxter, "Tropicando" > **Soundtrack Links**: [Spotify](https://open.spotify.com/track/63TCv4M85eKqUWT6Etu3UN) | [YouTube](https://www.youtube.com/watch?v=-2cmRd0DrVQ) > **Vibe Match**: Lush vibraphone melodies and brassy, eccentric trumpet honks, for a male whose nasal cavity is shaped to make loud, deep-sounding calls. ## Biological Superpowers & Stats - **Taxonomy**: *Nasalis larvatus* - **Danger Level**: Low - **Conservation Status**: Endangered ([IUCN Red List](https://doi.org/10.2305/iucn.uk.2021-1.rlts.t14352a195372486.en)) - **Superpower**: An oversized nose that amplifies a male's calls, making them louder than a female's and useful for warning the group of danger. - **Habitat**: Mostly coastal mangrove forests and lowland rainforest along rivers on Borneo, in Malaysia, Indonesia and Brunei - **Diet**: Mostly leaves and fruit, preferring young leaves and unripe fruit, plus flowers, bark and insects - **Tags**: primate, freshwater, wetlands, rainforest ## Natural History & Behavior ## A Nose Built to Be Heard Male proboscis monkeys (*Nasalis larvatus*) grow a large, bulbous nose unlike any other primate's. It droops over the mouth and sometimes tops 4 inches (10.1 cm). Many groups have one adult male, several females and their young, while other males live in bachelor groups. Earlier studies found males in breeding groups have bigger noses than bachelors, and bigger-nosed males tend to have more adult females in their group. The nose may let males make louder or deeper honks and roars. A 2024 study of skulls strongly backed both roles, display and sound. A male's bony nose opening keeps growing after his adult teeth are in, which fits a display. His nasal cavity is shaped to make loud, deep-sounding calls. Males can weigh up to 50 pounds (22 kg) and measure 29 to 30 inches (73 to 76 cm) from head to belly, with a tail nearly as long as the body. Females are much smaller, averaging 22 pounds (10 kg) and 24 to 25 inches (61 to 64 cm). In captivity, the record lifespan is 25.1 years. The species lives only on Borneo, in Malaysia, Indonesia and Brunei. It is found mostly in coastal mangrove forests or in lowland rainforest along rivers. ## A Monkey That Chews Like a Cow One group studied along a river in Sabah, Malaysia, spent about three-quarters of its time resting and a fifth feeding. Young leaves took nearly two-thirds of that feeding time and fruit about a quarter, and over 90% of the fruit feeding was on unripe fruit. When proboscis monkeys do eat ripe fruit, they usually pick out the seeds and leave the rest, because its sugars can cause severe indigestion. Their big bellies hold a stomach with several chambers that helps them digest fiber-rich plants. > **A first for primates** In 2011, scientists reported 23 wild proboscis monkeys bringing food back up from the stomach to chew it again, the first time this had been seen in a primate. Ruminants such as cattle do it far more consistently. Scientists watched one wild male for 169 days and saw him do it on 11 of them, mostly in the morning. Researchers call it a "facultative" strategy, meaning the monkeys use it only some of the time. A 2015 study of four captive monkeys found their digestion lacks the typical features of a ruminant's, which may explain why. Their droppings hold smaller food particles than other primates', one clue that they rechew. ## Built to Cross Rivers Proboscis monkeys rarely come down from the trees. When they do, it's usually to escape a predator or cross a river. Webbed fingers and toes, rare among primates, help them swim. Often they leap far out from high in the canopy to keep the swim short, splaying their arms and legs, then tucking them in just before they hit the water. Clouded leopards and crocodiles may be important predators. A 2008 study in Sabah recorded clouded leopards killing two young females from one group, an infant and a juvenile. It suggested adult males in one-male groups act as protectors. ## Under Threat The IUCN Red List classifies the proboscis monkey as Endangered, and its numbers are falling. Habitat loss is a major cause. Across Borneo, forests are being cleared for timber and farms, palm oil and rubber plantations have replaced large areas, and mangroves are being cut down for shrimp farms. ## Frequently Asked Questions ### Why do male proboscis monkeys have such enormous noses? The nose seems to do two jobs. As a visual signal, males in breeding groups have bigger noses than males in all-male groups, and bigger-nosed males tend to have more adult females in their group. As a sound signal, the nose may let males make louder or deeper honks and roars. A 2024 study of skulls found strong support for both jobs. *(Source: [Balolia & Fitzgerald 2024]())* ### Why can proboscis monkeys live on a diet that would upset other monkeys? Their stomach. Proboscis monkeys are one of the only primates able to digest the plants of Borneo's mangrove forests, which are rich in tannins, bitter chemicals that can be toxic. Their chambered stomach breaks down the tannins along with the huge amount of fiber they eat. Some researchers think this is why the species first lived in coastal mangroves, and the same ability let it spread to forests further inland. *(Source: [New England Primate Conservancy]())* ### How do proboscis monkeys escape predators like clouded leopards? By dropping into the water. Groups resting in trees tend to pick branches directly above the water. The slender branches shake when a predator such as a clouded leopard comes too close, which works as an alarm. If the monkeys have to flee, they can drop into the water and swim to safety. *(Source: [New England Primate Conservancy]())* ## Sources 1. [Proboscis Monkey, Nasalis larvatus. New England Primate Conservancy.]() 2. [Nasalis larvatus. AnAge: The Animal Ageing and Longevity Database, Human Ageing Genomic Resources.]() 3. [Boonratana et al. (2021). Nasalis larvatus. The IUCN Red List of Threatened Species 2021: e.T14352A195372486.]() 4. [Balolia & Fitzgerald (2024). Male proboscis monkey cranionasal size and shape is associated with visual and acoustic signalling. Scientific Reports.]() 5. [Matsuda et al. (2011). Regurgitation and remastication in the foregut-fermenting proboscis monkey (Nasalis larvatus). Biology Letters.]() 6. [Matsuda et al. (2015). Excretion patterns of solute and different-sized particle passage markers in foregut-fermenting proboscis monkey (Nasalis larvatus) do not indicate an adaptation for rumination. Physiology & Behavior.]() 7. [Matsuda, Tuuga & Higashi (2009). The feeding ecology and activity budget of proboscis monkeys. American Journal of Primatology.]() 8. [Matsuda, Tuuga & Higashi (2008). Clouded leopard (Neofelis diardi) predation on proboscis monkeys (Nasalis larvatus) in Sabah, Malaysia. Primates.]() *Published September 1, 2026. Last updated September 16, 2026.* ```json { "@context": "https://schema.org", "@graph": [ { "@type": "Article", "@id": "https://animaltracks.wiki/animals/proboscis-monkey/#article", "isPartOf": { "@id": "https://animaltracks.wiki/#website" }, "headline": "Proboscis Monkey (Nasalis larvatus) | AnimalTracks.wiki", "description": "An oversized nose that works as both a visual badge and a vocal amplifier, webbed fingers and toes that help it swim across rivers, and a cow-like habit of bringing food back up to chew it again.", "image": [ "https://animaltracks.wiki/images/animals/proboscis-monkey-1.webp" ], "datePublished": "2026-09-01", "dateModified": "2026-09-16", "author": [ { "@type": "Organization", "name": "AnimalTracks.wiki Editorial Team", "url": "https://animaltracks.wiki" } ], "publisher": { "@type": "Organization", "@id": "https://animaltracks.wiki/#organization", "name": "AnimalTracks.wiki", "url": "https://animaltracks.wiki", "logo": { "@type": "ImageObject", "url": "https://animaltracks.wiki/icon-512.png" } }, "mainEntityOfPage": "https://animaltracks.wiki/animals/proboscis-monkey/", "citation": [ { "@type": "CreativeWork", "name": "Proboscis Monkey, Nasalis larvatus", "url": "https://www.neprimateconservancy.org/proboscis-monkey", "publisher": { "@type": "Organization", "name": "New England Primate Conservancy" } }, { "@type": "CreativeWork", "name": "Nasalis larvatus", "url": "https://genomics.senescence.info/species/entry.php?species=Nasalis_larvatus", "publisher": { "@type": "Organization", "name": "AnAge: The Animal Ageing and Longevity Database, Human Ageing Genomic Resources" } }, { "@type": "ScholarlyArticle", "name": "Nasalis larvatus. The IUCN Red List of Threatened Species 2021: e.T14352A195372486", "url": "https://doi.org/10.2305/iucn.uk.2021-1.rlts.t14352a195372486.en", "author": "Boonratana et al.", "datePublished": "2021", "isPartOf": { "@type": "Periodical", "name": "The IUCN Red List of Threatened Species" }, "identifier": "doi:10.2305/iucn.uk.2021-1.rlts.t14352a195372486.en" }, { "@type": "ScholarlyArticle", "name": "Male proboscis monkey cranionasal size and shape is associated with visual and acoustic signalling", "url": "https://doi.org/10.1038/s41598-024-60665-8", "author": "Balolia & Fitzgerald", "datePublished": "2024", "isPartOf": { "@type": "Periodical", "name": "Scientific Reports" }, "identifier": "doi:10.1038/s41598-024-60665-8" }, { "@type": "ScholarlyArticle", "name": "Regurgitation and remastication in the foregut-fermenting proboscis monkey (Nasalis larvatus)", "url": "https://doi.org/10.1098/rsbl.2011.0197", "author": "Matsuda et al.", "datePublished": "2011", "isPartOf": { "@type": "Periodical", "name": "Biology Letters" }, "identifier": "doi:10.1098/rsbl.2011.0197" }, { "@type": "ScholarlyArticle", "name": "Excretion patterns of solute and different-sized particle passage markers in foregut-fermenting proboscis monkey (Nasalis larvatus) do not indicate an adaptation for rumination", "url": "https://doi.org/10.1016/j.physbeh.2015.05.020", "author": "Matsuda et al.", "datePublished": "2015", "isPartOf": { "@type": "Periodical", "name": "Physiology & Behavior" }, "identifier": "doi:10.1016/j.physbeh.2015.05.020" }, { "@type": "ScholarlyArticle", "name": "The feeding ecology and activity budget of proboscis monkeys", "url": "https://doi.org/10.1002/ajp.20677", "author": "Matsuda, Tuuga & Higashi", "datePublished": "2009", "isPartOf": { "@type": "Periodical", "name": "American Journal of Primatology" }, "identifier": "doi:10.1002/ajp.20677" }, { "@type": "ScholarlyArticle", "name": "Clouded leopard (Neofelis diardi) predation on proboscis monkeys (Nasalis larvatus) in Sabah, Malaysia", "url": "https://doi.org/10.1007/s10329-008-0085-2", "author": "Matsuda, Tuuga & Higashi", "datePublished": "2008", "isPartOf": { "@type": "Periodical", "name": "Primates" }, "identifier": "doi:10.1007/s10329-008-0085-2" } ], "about": { "@type": "Taxon", "name": "Proboscis Monkey", "scientificName": "Nasalis larvatus", "description": "An oversized nose that amplifies a male's calls, making them louder than a female's and useful for warning the group of danger." } }, { "@type": "FAQPage", "@id": "https://animaltracks.wiki/animals/proboscis-monkey/#faq", "mainEntity": [ { "@type": "Question", "name": "Why do male proboscis monkeys have such enormous noses?", "acceptedAnswer": { "@type": "Answer", "text": "The nose seems to do two jobs. As a visual signal, males in breeding groups have bigger noses than males in all-male groups, and bigger-nosed males tend to have more adult females in their group. As a sound signal, the nose may let males make louder or deeper honks and roars. A 2024 study of skulls found strong support for both jobs.", "citation": { "@type": "ScholarlyArticle", "name": "Male proboscis monkey cranionasal size and shape is associated with visual and acoustic signalling", "url": "https://doi.org/10.1038/s41598-024-60665-8", "author": "Balolia & Fitzgerald", "datePublished": "2024", "isPartOf": { "@type": "Periodical", "name": "Scientific Reports" }, "identifier": "doi:10.1038/s41598-024-60665-8" } } }, { "@type": "Question", "name": "Why can proboscis monkeys live on a diet that would upset other monkeys?", "acceptedAnswer": { "@type": "Answer", "text": "Their stomach. Proboscis monkeys are one of the only primates able to digest the plants of Borneo's mangrove forests, which are rich in tannins, bitter chemicals that can be toxic. Their chambered stomach breaks down the tannins along with the huge amount of fiber they eat. Some researchers think this is why the species first lived in coastal mangroves, and the same ability let it spread to forests further inland.", "citation": { "@type": "CreativeWork", "name": "Proboscis Monkey, Nasalis larvatus", "url": "https://www.neprimateconservancy.org/proboscis-monkey", "publisher": { "@type": "Organization", "name": "New England Primate Conservancy" } } } }, { "@type": "Question", "name": "How do proboscis monkeys escape predators like clouded leopards?", "acceptedAnswer": { "@type": "Answer", "text": "By dropping into the water. Groups resting in trees tend to pick branches directly above the water. The slender branches shake when a predator such as a clouded leopard comes too close, which works as an alarm. If the monkeys have to flee, they can drop into the water and swim to safety.", "citation": { "@type": "CreativeWork", "name": "Proboscis Monkey, Nasalis larvatus", "url": "https://www.neprimateconservancy.org/proboscis-monkey", "publisher": { "@type": "Organization", "name": "New England Primate Conservancy" } } } } ] }, { "@type": "MusicRecording", "name": "Tropicando", "byArtist": { "@type": "MusicGroup", "name": "Les Baxter" }, "genre": "Jazz-Funk, Soul & Lounge Fusion", "url": "https://open.spotify.com/track/63TCv4M85eKqUWT6Etu3UN" } ] } ```