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Two-toed sloth
Two-toed sloth
Two-toed sloth
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Two-toed sloths[1]
Hoffmann's two-toed sloth (C. hoffmanni)
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Pilosa
Superfamily: Mylodontoidea
Family: Choloepodidae
Gray, 1871[2]
Genus: Choloepus
Illiger, 1811[1]
Type species
Bradypus didactylus
Linnaeus, 1758
Species

Choloepus is a genus of xenarthran mammals from Central and South America within the monotypic family Choloepodidae, consisting of two-toed sloths,[3] sometimes also called two-fingered sloths.[4] The two species of Choloepus (which means "lame foot" in Ancient Greek[5]), Linnaeus's two-toed sloth (Choloepus didactylus) and Hoffmann's two-toed sloth (Choloepus hoffmanni), were formerly believed on the basis of morphological studies to be the only surviving members of the sloth family Megalonychidae,[6] but have now been shown by molecular results to be closest to extinct ground sloths of the family Mylodontidae.[4][3]

Extant species

[edit]
Genus Choloepus – Illiger, 1811 – two species
Common name Scientific name and subspecies Range Size and ecology IUCN status and estimated population
Linnaeus's two-toed sloth

Choloepus didactylus
(Linnaeus, 1758) 		Northern South America, found in Venezuela, the Guyanas, Colombia, Ecuador, Peru, and Brazil north of the Amazon River
Map of range 		Size:

Habitat:

Diet: 		 LC 


Hoffmann's two-toed sloth

Choloepus hoffmanni
Peters, 1858

Five subspecies
  • C. h. hoffmanni, Peters, 1858 – Honduras, Nicaragua, Costa Rica, Panama
  • C. h. agustinus, Allen, 1913 – Venezuela, western Colombia, northern Ecuador
  • C. h. capitalis, Allen, 1913 – western Ecuador
  • C. h. juruanus, Lönnberg, 1942 – Brazil, Bolivia, extreme eastern Peru
  • C. h. pallescens, Lönnberg, 1928 – Peru
Central America and northwestern South America
Map of range 		Size:

Habitat:

Diet: 		 LC 



Evolution

[edit]

A study of retrovirus and mitochondrial DNA suggests that C. didactylus and C. hoffmani diverged 6 to 7 million years ago.[7] Furthermore, based on cytochrome c oxidase subunit I sequences, a similar divergence date (c. 7 million years ago) between the two populations of C. hofmanni separated by the Andes has been reported.[8] Their ancestors evolved with marine vertebrae, the three toed-sloth and the manatee are the only other mammals with similar vertebrae.[9]

Relation to the three-toed sloth

[edit]

Both types of sloth tend to occupy the same forests; in most areas, a particular species of the somewhat smaller and generally slower-moving three-toed sloth (Bradypus) and a single species of the two-toed type will jointly predominate. Although similar in overall appearance, the relationship between the two genera is not close. Recent phylogenetic analyses[10] support analysis of morphological data from the 1970s and 1980s, indicating the two genera are not closely related and adapted to their arboreal lifestyles independently. It was unclear from this work from which ground-dwelling sloth taxa the three-toed sloths evolved. Based on the morphological comparisons, it was thought the two-toed sloths nested phylogenetically within one of the divisions of Caribbean sloths.[11] Though data has been collected on over 33 different species of sloths by analyzing bone structures, many of the relationships between clades on a phylogenetic tree were unclear.[12]

Much of the morphological evidence to support the hypothesis of diphyly has been based on the structure of the inner ear.[13] Most morphological studies have concluded that convergent evolution is the mechanism that resulted in today's two genera of tree sloths. This means that the extant genera evolved analogous traits, such as locomotion methods, size, habitat, and many other traits independently from one another as opposed to from their last common ancestor. This makes tree sloths “one of the most striking examples of convergent evolution known among mammals”.[12]

Recently obtained molecular data from collagen[3] and mitochondrial DNA[4] sequences fall in line with the diphyly (convergent evolution) hypothesis, but have overturned some of the other conclusions obtained from morphology. These investigations consistently place two-toed sloths close to mylodontids and three-toed sloths within Megatherioidea, close to Megalonyx, megatheriids and nothrotheriids. They make the previously recognized family Megalonychidae polyphyletic, with both two-toed sloths and the Caribbean sloths being moved out of that family and away from Megalonyx. Caribbean sloths are placed in a separate, basal branch of the sloth evolutionary tree.[3][4]

The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data (see Fig. 4 of Presslee et al., 2019).[3]

Folivora

† Megalocnidae (Caribbean sloths)

Characteristics

[edit]
Display of two "fingers" on forelimbs and three toes on hindlimbs

The name "two-toed sloth" was intended to describe an anatomical difference between the genera Choloepus and Bradypus, but does so in a potentially misleading way. Members of Choloepus have two digits on their forelimbs (the thoracic limbs) and three digits on their hindlimbs (the pelvic limbs), while members of Bradypus have three digits on all limbs. Although the term "two-fingered" sloth is arguably less misleading, the shorter "two-toed" is much more widely used.[note 1]

Members of Choloepus are larger than three-toed sloths, having a body length of 58 to 70 centimetres (23 to 28 in), and weighing 4 to 8 kilograms (8.8 to 17.6 lb). Other distinguishing features include a more prominent snout, longer fur, and the absence of a tail.[14]

Behaviour

[edit]

Two-toed sloths spend most of their lives hanging upside down from trees. They cannot walk, so they pull hand-over-hand to move around, which is at an extremely slow rate. Almost all of their movement comes from this suspended upside down position, at a higher degree than even three-toed sloths. As a result, they tend to gravitate towards less vertical portions of trees.[15][16] Being predominantly nocturnal, their fur, which grows greenish algae to blend in, is their main source of protection.[17] Their body temperatures depend at least partially on the ambient temperature; they cannot shiver to keep warm, as other mammals do, because of their unusually low metabolic rates and reduced musculature.[14] Two-toed sloths also differ from three-toed sloths in their climbing behavior, preferring to descend head first.

Lifecycle

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Young C. hoffmanni being raised in a wildlife rescue center in the Osa Peninsula, Costa Rica

Two-toed sloths have a gestation period of six months to a year, depending on the species. Their ovarian cycle lasts around 31 to 33 days, independently of the seasons but dependent on the species.[18] The mother gives birth to a single young, while hanging upside down. The young are born with claws, and are weaned after about a month, although they will remain with the mother for several more months, and do not reach maturity until the age of three years, in the case of females, or four to five years, in the case of males.[16] During natal dispersion, two-toed sloths prefer tropical forests over other types of habitat, often using riparian forest buffers to disperse. Although they also occupy shade-grown cacao plantations, they avoid open pastures.[19]

Feeding

[edit]

They eat primarily leaves, but also shoots, fruits, nuts, berries, bark, some native flowers, and even some small vertebrates.[20] In addition, when they cannot find food, they have been known to eat the algae that grow on their fur for nutrients.[21] They have also been observed using mineral licks.[22][23] They have large, four-chambered stomachs, which help to ferment the large amount of plant matter they eat.[24] Food can take up to a month to digest due to their slow metabolism.[14] Depending on when in the excretion cycle a sloth is weighed, urine and feces may account for up to 30% of the animal's body weight.[25] They get most of their fluids from water in the leaves that they eat but sloths have also been observed drinking directly from rivers.[citation needed]

Dentition and skeleton

[edit]

Two-toed sloths have a reduced, ever growing dentition, with no incisors or true canines, which overall lacks homology with the dental formula of other mammals. Their first tooth is very canine-like in shape and is referred to as a caniniform. It is used for tearing small chunks off of their food, as well as for defense against predators.[26] It is separated from the other teeth, or molariforms, by a diastema. The molariforms are used specifically for grinding and are mortar and pestle-like in appearance and function. Thus, they can grind food for easier digestibility, which takes the majority of their energy. The dental formula of two-toed sloths is: 45 (unau)

Two-toed sloths are unusual among mammals in possessing as few as five cervical vertebrae, which may be due to mutations in the homeotic genes.[27] All other mammals have seven cervical vertebrae,[28] other than the three-toed sloth and the manatee.

Musculature

[edit]

Two-toed sloths generally have similar musculature to that of other mammals. This includes their zygomaticus muscles, their superficial masseter, their deep masseter, and their medial and lateral pterygoids. Additionally, a specific section of their anterior temporalis is arranged vertically, to allow them to sharpen their caniniform teeth.[26] They tend to have stronger flexor muscles in their fore- and hindlimbs, as well as their shoulders.[15]

Notes

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References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Two-toed sloth

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from Grokipedia
The two-toed sloth ( Choloepus) comprises two extant species of arboreal xenarthran mammals in the family , distinguished by their possession of only two functional claws on the forelimbs, nocturnal lifestyle, and slow, energy-conserving metabolism adapted for life in the canopy of tropical rainforests. These sloths, native to Central and , are herbivores that primarily consume leaves, fruits, and buds, with specialized digestive systems featuring multi-chambered stomachs to process fibrous vegetation over extended periods of up to 2.5 days per meal. Unlike their three-toed counterparts in the Bradypus, two-toed sloths lack specialized teeth for grinding and exhibit a broader diet that occasionally includes , while their fur often hosts symbiotic that provide through a greenish tint during wet seasons. The two recognized species are Hoffmann's two-toed sloth (Choloepus hoffmanni), ranging from Nicaragua through Central America to northern South America including parts of Brazil and Bolivia, and Linnaeus's two-toed sloth (Choloepus didactylus), found in northern South America from Venezuela to Peru and Brazil. Both species inhabit lowland and montane rainforests up to elevations of 3,000 meters, preferring areas with continuous tree canopy for foraging and resting, though they are capable swimmers and occasionally descend to the ground to defecate roughly once a week. Adults typically measure 58–70 cm in head-body length and weigh 4–8 kg, with dense, coarse fur that slants in the direction of limb movement to shed water and debris, and a body temperature fluctuating between 24–33°C due to their low metabolic rate, which is 40–60% of that expected for mammals of similar size. Behaviorally, two-toed sloths are solitary and territorial, with individuals maintaining home ranges of about 10 acres and moving only 36–38 meters per day in the trees at speeds of 1.8–2.4 meters per minute. They spend 15–18 hours daily sleeping or resting upside down, emerging at night to for 6–11 hours, and communicate minimally through marking or distress calls like hissing or bleating, relying instead on and immobility for defense against predators such as eagles, jaguars, and ocelots. occurs year-round, with females giving birth to a single precocial young after a of 9–11 months; the offspring clings to the mother's for 9–12 months before , and lifespan in the wild averages 15–20 years, extending beyond 30 years in captivity. Conservationally, both species are classified as Least Concern by the IUCN due to their wide distribution and presumed stable populations, though habitat loss from poses a localized , and they are listed under Appendix III in some regions to regulate . Efforts to protect two-toed sloths focus on preservation, as their dependence on intact canopies makes them vulnerable to fragmentation, despite their adaptability compared to more specialized three-toed sloths.

Taxonomy

Extant species

The genus Choloepus includes two extant species of two-toed sloths: Linnaeus's two-toed sloth (Choloepus didactylus) and Hoffmann's two-toed sloth (Choloepus hoffmanni). Choloepus didactylus was originally described by Carl Linnaeus in 1758 based on specimens from South America, while Choloepus hoffmanni was formally described by Wilhelm Peters in 1858, honoring the collector Carl Hoffmann. No subspecies are currently recognized for either species, reflecting their distinct morphological and genetic profiles. The two species can be distinguished primarily by pelage characteristics and geographic distribution. C. didactylus typically exhibits shorter, denser fur that is uniformly brown to grayish-brown, often without prominent markings on the head or s. In contrast, C. hoffmanni has longer, wavier fur that is lighter overall, with a pale throat, darker chest, and gray-brown to tan coloration, sometimes accented by darker shading on the head and back but lacking dark and markings. C. didactylus is distributed in northern north of the , with recent confirmed records (as of 2024) extending into the central-southern Amazon (e.g., , ), up to 820 km south of previous limits. C. hoffmanni occurs from through northern and western south of the Amazon, with partial overlap () in Andean foothills, western Amazonia, and now central-southern regions. Recent molecular analyses, including mitochondrial genome sequencing, have confirmed the genetic distinctiveness and species boundaries of C. didactylus and C. hoffmanni, supporting their separation as valid extant taxa within Choloepus.

Phylogenetic position

Two-toed sloths are classified within the order , suborder Folivora, and family Choloepodidae, which encompasses the genus Choloepus and distinguishes them from the three-toed sloths in the family Bradypodidae. This classification reflects their position as xenarthrans, a unique mammalian superorder that also includes anteaters and armadillos, with Folivora representing the sloth lineage specialized for arboreal folivory. Some sources refer to the family as , but recent phylogenetic studies favor Choloepodidae to distinguish the extant lineage from extinct megalonychid sloths. Genetic studies utilizing mitochondrial and nuclear DNA have established Choloepodidae as a distinct evolutionary lineage within Folivora, diverging from the Bradypodidae clade approximately 29 million years ago during the late Oligocene. For instance, analyses of complete mitogenomes from extant and extinct sloths confirm this split, highlighting widespread morphological convergence between the two families despite their close relationship as the only surviving folivorans. Key molecular markers, such as the cytochrome b gene from mitochondrial DNA, have been instrumental in demonstrating the monophyly of Choloepus, with Bayesian inference supporting robust clustering of the two species and their affinity to mylodontid sloths like Mylodon darwinii. While three-toed sloths represent the closest living relatives of two-toed sloths, molecular phylogenies reveal that Choloepodidae exhibits a stronger genetic affinity to certain extinct sloth groups, particularly the mylodontids, rather than the megalonychids, which align more closely with Bradypus. This positioning underscores the deep divergence within Folivora, where ancient mitogenomic data reposition two-toed sloths within the superfamily Mylodontoidea, separate from the Megatherioidea containing three-toed sloths and their fossil kin.

Evolution

Fossil record

The lineage leading to modern two-toed sloths (genus Choloepus) is part of the mylodontoid radiation within Folivora, with the earliest s of this group appearing in during the Deseadan South American Land Mammal Age, approximately 29–30 million years ago. Choloepus-like forms are represented in the record, around 10–11 million years ago, including enigmatic mylodontoids such as Eionaletherium tanycnemius from the Urumaco Formation in northern . These early relatives were terrestrial , differing from the arboreal lifestyle of extant Choloepus . Key fossils from the and Pleistocene highlight the diversity of Choloepus relatives in the family, such as Mylodon darwinii from southern , known from caves in dated to about 13,000 years before present. Molecular dating suggests the divergence of the Choloepus lineage from the (Bradypus) lineage occurred around 28–36 million years ago, during the . Most fossil relatives of two-toed sloths, including the large ground-dwelling mylodontids, became extinct by the end of the Pleistocene, approximately 10,000–12,000 years ago, coinciding with rapid climate warming at the Pleistocene-Holocene boundary and the arrival of humans in the Americas. The modern arboreal form of Choloepus likely evolved after the late Miocene, adapting to forested environments as ground sloth diversity declined. Recent paleontological research using protein sequences from fossils has provided strong evidence linking extant Choloepus directly to mylodontid , resolving long-standing uncertainties in phylogeny by confirming Choloepus as a surviving mylodontoid rather than a megalonychid. Recent total-evidence analyses (as of 2024) support crown Folivora diversification around 45 Ma, with the Choloepus-Bradypus split circa 25–30 Ma. This analysis, applied to specimens from sites across and the dating from the early to the late , underscores the deep evolutionary continuity within the lineage.

Relation to three-toed sloths

Two-toed sloths (genus Choloepus, family Megalonychidae) and three-toed sloths (genus Bradypus, family Bradypodidae) represent two distinct evolutionary lineages that have converged on similar arboreal adaptations despite their distant relationship. Both groups independently evolved from ground-dwelling ancestors in the order , developing slow metabolic rates, suspensory locomotion, and leaf-based diets as adaptations to life in [tropical forest](/page/tropical forest) canopies. This [convergent evolution](/page/convergent evolution) is evident in their shared morphological traits, such as elongated limbs and curved claws for hanging, which facilitate energy-efficient movement in trees, even though their common ancestor likely lived on the forest floor millions of years ago. Anatomically, notable differences distinguish the two groups, reflecting their separate evolutionary paths. Two-toed sloths typically possess six or seven , limiting head rotation to about 90 degrees, whereas three-toed sloths have eight to ten , enabling nearly 360-degree head mobility that aids in scanning for predators and food without repositioning their bodies. In terms of , both lack incisors and canines in the traditional sense, featuring peg-like, ever-growing teeth suited for grinding foliage; however, two-toed sloths exhibit more developed, canine-like upper teeth and a slightly more complex arrangement (five upper and four lower cheek teeth per side), while three-toed sloths have simpler, uniform peg teeth with vestigial or absent upper canines that are often shed postnatally. Ecologically, two-toed and three-toed sloths occupy overlapping habitats but differ in activity patterns and strategies. Two-toed sloths are primarily nocturnal and exhibit greater mobility, allowing them to cover larger home ranges and occasionally descend to the ground; in contrast, three-toed sloths are mostly diurnal and more sedentary, relying on symbiotic growth in their fur for against predators. Both are folivores, consuming primarily leaves low in nutrients, but two-toed sloths supplement their diet more frequently with fruits, flowers, , and even small vertebrates, enabling slightly higher energy expenditure compared to the stricter leaf diet of three-toed sloths. Molecular evidence indicates a deep between the two genera, with phylogenetic analyses using relaxed molecular clocks estimating their split at approximately 23–30 million years ago at the Oligocene-Miocene boundary. This temporal separation underscores their placement in different families, with no evidence of hybridization between Choloepus and Bradypus species, as confirmed by chromosomal studies showing distinct karyotypes and no shared synapomorphies.

Physical characteristics

External morphology

Two-toed sloths (genus Choloepus) are medium-sized arboreal mammals, with adults typically measuring 58 to 70 cm in head-body length and weighing between 4 and 8 kg. There is no notable in size or external appearance between males and females. Their is coarse and shaggy, providing insulation and a for symbiotic organisms, and is generally grayish-brown in color, though it can appear tan to buffy brown. This often hosts blue-green (), which grow in grooves along the hair shafts, imparting a greenish tint that enhances against the canopy. The grows in the opposite direction to most mammals—from the belly toward the back—to prevent water accumulation during rain and facilitate drying. The head is rounded and flat, featuring a short snub nose, small dark eyes, and tiny rounded ears that are often obscured by . Two-toed sloths lack a entirely, a characteristic for their suspensory lifestyle. Their limbs are long and of nearly equal length, with the forelimbs bearing only two syndactylous digits (fused fingers) tipped by strongly curved claws measuring 8 to 10 cm in length, while the hindlimbs have three clawed digits. These specialized claws enable secure suspension from branches and are subequal in size across the limbs. In terms of sensory adaptations, two-toed sloths possess poor and colorblindness due to rod monochromacy, with vision adapted for dim light. They compensate with a keen , which aids in locating food and navigating their environment, as their hearing is also relatively underdeveloped.

Internal anatomy

The skeletal system of two-toed sloths (genus Choloepus) is highly specialized for an arboreal, suspensory lifestyle, featuring a total of approximately 58 vertebrae that provide flexibility and support during prolonged hanging. The neck is relatively short and robust, with 6-7 —fewer than the typical seven found in most mammals—allowing limited rotation of up to 90 degrees while maintaining essential for upside-down postures. Thoracolumbar vertebrae number 18-27, contributing to an elongated torso that distributes weight evenly across branches, while the robust limbs exhibit thickened bones and fused elements in the carpus and tarsus, enhancing stability and grip strength for suspension without rapid movement. Dentition in two-toed sloths is simplified and adapted for tough, fibrous , lacking incisors and canines entirely, which aligns with their xenarthran ancestry. The dental formula is 5/4, consisting of 4-5 peg-like, cylindrical molars per quadrant that are ever-growing, enamel-free, and composed primarily of orthodentine surrounding softer inner . These teeth function through continuous wear and regrowth, forming blunt grinding surfaces suited to mashing leaves rather than precise cutting. Muscular anatomy emphasizes energy conservation and sustained grip over speed or power, with total muscle mass comprising only 25-30% of body weight—significantly less than the 40-50% typical in other mammals of comparable size. Flexor muscles in the limbs and shoulders are disproportionately powerful, enabling strong, prolonged clinging to branches via hook-like claws, whereas extensor muscles are notably weaker, reflecting reduced need for extension in a primarily suspensory posture. The musculature is dominated by slow-twitch fibers rich in myoglobin and mitochondria, which support low metabolic rates and fatigue-resistant contractions ideal for the sloth's slow lifestyle. The digestive system features a large, multi-chambered stomach divided into four compartments that harbor symbiotic bacteria and protozoa for fermenting cellulose-rich foliage, enabling nutrient extraction from low-energy diets. This fermentation process occurs slowly, with the stomach often holding up to 30% of the animal's body weight in undigested material at any time.

Distribution and habitat

Geographic range

Two-toed sloths, genus Choloepus, are native to Central and northern South America, where they inhabit tropical forest canopies. The two extant species exhibit partially overlapping distributions, with sympatry occurring in the Andean foothills and western Amazon basin. Hoffmann's two-toed sloth (Choloepus hoffmanni) has a disjunct range, with a northern population extending from through , , and in , and into northern including western , northern , and western . A southern population is found in north-central , southwestern , and central . (Choloepus didactylus) occupies northern , ranging from and through , , , , and northern north of the . Both species are restricted to well-forested habitats, with their combined range fragmented by ongoing . These sloths occur from up to elevations of approximately 2,400–3,300 m, depending on the and local . A 2024 study in Biotropica provided evidence of a southern extension for C. didactylus in the Amazon region, documenting new records up to 820 km south of its previously known distribution limits through camera trapping and genetic sampling. Global population estimates for two-toed sloths are unavailable due to their elusive, arboreal nature, which complicates density assessments. Both are classified as Least Concern by the IUCN (assessments 2022), reflecting their wide distributions and suspected stable despite ongoing habitat loss and fragmentation.

Habitat preferences

Two-toed sloths (genus Choloepus) exhibit a strong preference for mature, undisturbed tropical rainforests and cloud forests across their Neotropical range, where they favor canopies dense with lianas and epiphytes that facilitate movement and provide camouflage. These habitats offer the structural complexity needed for their arboreal lifestyle, with records also indicating occasional use of forests in coastal areas, particularly for species like (C. hoffmanni). They avoid open areas, dry forests, and highly fragmented landscapes, selecting instead moist evergreen forests that support high canopy connectivity. In terms of microhabitat use, two-toed sloths are strictly arboreal, occupying heights between 6 and 30 meters in the forest canopy, often in trees 18–27 meters tall with dense crowns and cover. They spend much of their time in the upper canopy layers, sleeping in tangled or crotches of branches, and descend only infrequently for or mineral licks. During natal dispersal, individuals prioritize riparian forest buffers and continuous forested corridors to navigate human-modified landscapes, enhancing connectivity between patches and reducing exposure to ground predators. These sloths are adapted to humid tropical climates characterized by temperatures of 20–30°C and high annual rainfall exceeding 2,000 mm, with their variable body temperatures ranging from 24–33°C reflecting limited thermoregulatory capacity suited to stable, warm environments. However, recent 2024 research highlights their vulnerability to , projecting that metabolic rates in high-altitude populations could become untenable under ambient temperature rises greater than 2°C, as their low-energy lifestyle and poor heat dissipation hinder to warmer conditions. This sensitivity underscores the importance of preserving intact forest habitats to buffer against rising temperatures.

Behavior

Activity patterns

Two-toed sloths (genus Choloepus) exhibit primarily nocturnal activity patterns, with most foraging and movement occurring during nighttime hours, typically beginning about one hour after sunset and ceasing by dawn. They rest during the day, often hanging upside down from tree branches in a state of minimal activity, sleeping and resting for approximately 13 hours per day. This nocturnal rhythm contrasts with the more diurnal or cathemeral tendencies observed in three-toed sloths (genus Bradypus), where activity is less strictly confined to nighttime. Recent field studies using collar-based monitoring have revealed some flexibility, with two-toed sloths showing cathemeral behavior in certain environments, including short bursts of activity (averaging 5-6 minutes) distributed across both day and night without a strict circadian peak. Their low metabolic rate, ranging from 40-45% of that expected for their body size based on standard mammalian scaling, enables extended periods of rest and contributes to their -conserving lifestyle. To further minimize expenditure, two-toed sloths enter torpor-like states, during which their body fluctuates widely between 24-33°C in response to ambient conditions, rather than maintaining a constant internal . This physiological adaptation allows them to tolerate low food intake while avoiding the high costs of typical in other mammals. Seasonal variations influence their activity, with reduced movement and observed during dry seasons compared to wet periods, when they spend more time actively traversing their . Individuals maintain small home ranges of 1-3 ha on average, covering minimal daily distances of 10-40 m, often limited to a few dozen trees within their . A 2023 study in on rehabilitated Hoffmann's two-toed sloths (Choloepus hoffmanni) documented their post-release adjustment to wild patterns, showing increased nocturnal activity and similar to free-ranging individuals, though with overall lower rates due to predation.

Locomotion and social behavior

Two-toed sloths exhibit a distinctive form of characterized by slow, deliberate suspensory movements, including hanging, bridging, and clambering beneath branches using their long limbs and curved claws. This below-branch progression relies on a trot-like for stability during steady-state travel, with maximal speeds reaching up to 0.5 km/h in short bursts, though typical climbing rates are 1.8–2.4 m/min. Unlike true brachiation seen in , their motion involves no pendular mechanics, emphasizing energy-efficient suspension rather than swinging. Ground travel is rare and awkward, occurring primarily for , at speeds of approximately 16 m/hour as they drag their bodies forward. Field observations indicate that two-toed sloths spend approximately 70% of their time hanging motionless, even when awake, to minimize energy expenditure during their low-metabolic lifestyle. Recent 2024 research on sloth metabolism underscores this adaptation, revealing daily energy use as low as 234 kJ/kg for species like Choloepus hoffmanni, which supports their slow movement patterns amid limited caloric intake from folivorous diets. Locomotion is further optimized for vertical and horizontal canopy navigation, covering about 38 m of forest daily on average, with descent from trees occurring weekly. Socially, two-toed sloths are predominantly solitary, with adults maintaining individual home ranges of 1.2–6.5 ha that show overlap between sexes but little interaction beyond occasional encounters at feeding sites. Females with dependent young form the primary social unit, as offspring remain with their mothers for 9–12 months, inheriting parts of the maternal range upon independence. There is no evidence of territoriality or group formation, and aggression is minimal, limited to defensive displays rather than active conflict. Communication occurs mainly through vocalizations for defense and distress, including hisses resembling a deflating , low bleats lasting 30–90 seconds when threatened, and screams or grunts during confrontations. These sounds serve to deter predators or signal alarm rather than facilitate social , aligning with their solitary habits. Infants produce high-pitched bleats when separated from mothers, but adults are generally silent outside of defensive contexts.

Ecology

Diet and foraging

The diet of two-toed sloths (genus Choloepus) is predominantly folivorous, consisting primarily of leaves from various tree species, supplemented by fruits, flowers, and occasional or small vertebrates. Preferred leaf sources include those from Dipteryx panamensis, Anacardium excelsium, Sapium caudatum, and Terminalia amazonia, which provide a high-fiber, low-nutrient suited to their slow metabolic rate. This composition reflects an opportunistic yet selective approach to in the nutrient-poor canopy, where leaves form the bulk of available . Foraging occurs primarily at night through selective , where individuals use their acute to locate and clip tender young leaves and buds, consuming about 30-50 grams of per day (for 4-8 kg adults)—roughly 1-1.5% of their body weight on a dry basis. This low intake aligns with their energy-conserving lifestyle, allowing them to remain stationary for much of the day while expending minimal effort on acquisition. To eliminate waste, two-toed sloths descend to the just 1-2 times per week, a that minimizes exposure to ground predators but limits overall mobility. Additionally, two-toed sloths host symbiotic moths in their fur, which may contribute to nutrient recycling by depositing eggs and providing nitrogen-rich . Digestion in two-toed sloths is adapted for processing fibrous, low-quality via a complex multi-chambered that facilitates . Symbiotic gut microbes play a crucial role in breaking down , enabling nutrient extraction over extended retention times of 4-21 days, which maximizes yield from meager inputs. This process also supports low production through microbial of , reducing the need for high-protein intake and conserving water in their humid habitat. Key nutritional adaptations include urea-nitrogen recycling via stomach , akin to cecotrophy in other herbivores, which enhances protein efficiency from poor-quality leaves. Recent research highlights how this slow , while advantageous for low-energy , increases vulnerability to ; rising temperatures could impair efficiency by exceeding the narrow thermal tolerance of their metabolic pathways, particularly in highland populations.

Predators and defenses

Two-toed sloths face predation primarily from harpy eagles (Harpia harpyja), which target them in the canopy, as well as ground-dwelling predators such as ocelots (Leopardus pardalis), jaguars (Panthera onca), and large constrictors like (Boa constrictor) and anacondas (Eunectes murinus). These predators exploit the sloths' arboreal lifestyle, with eagles ambushing from above and terrestrial carnivores attacking during rare descents. Sloths are particularly vulnerable when they leave the trees to move between them, defecate, or change feeding sites, as their slow ground locomotion—averaging just 16.1 meters per hour—leaves them exposed to ambush by these agile hunters. To counter these threats, two-toed sloths rely heavily on passive defenses centered around concealment and minimal activity. Their fur often harbors and other epibionts, enhancing against the dappled forest canopy and reducing visibility to visually oriented predators like eagles and cats. Immobility serves as their primary anti-predator strategy; sloths typically remain motionless or adopt cryptic postures—hanging limply or blending into branches—for extended periods when potential threats are nearby, leveraging their slow to avoid detection. When camouflage fails, they can actively defend using their long, sharp claws (up to 10 cm) to slash at attackers and strong jaws with specialized canines to bite, though such confrontations are rare due to their generally docile nature. Vocalizations play a limited but targeted role in defense, particularly for family units. Adults may hiss aggressively when threatened, while distressed individuals emit low bleats; separated juveniles produce prolonged, high-pitched bleats lasting 30–90 seconds to signal alarm and attract maternal attention. Mothers provide protection by carrying infants ventrally on their belly for the first five weeks after birth, allowing the young to cling tightly with their own claws while remaining hidden against the parent's body. This ventral carriage shifts to dorsal positioning after begins around 4–5 weeks, but maternal vigilance persists for up to 9–12 months, with females grooming and defending offspring during vulnerable early stages. Predation exerts significant pressure on two-toed sloth populations, particularly among juveniles, where it ranks as a leading cause of mortality alongside natural factors like . In a 2023 study of rehabilitated Hoffmann's two-toed sloths (Choloepus hoffmanni) in central , predation accounted for most of the eight recorded deaths among 14 released individuals, resulting in a monthly of 0.72 ± 0.14—lower than rates observed in wild populations (typically >0.90 for adults). These rehabilitated sloths demonstrated learned anti-predator behaviors, such as increased canopy use and avoidance of open areas, which improved individual compared to pre-release expectations, though overall outcomes highlighted the challenges of post-rehabilitation adaptation in predator-rich habitats.

Reproduction and life cycle

Mating and gestation

Two-toed sloths exhibit a polygynous characterized by males with multiple females without forming pair bonds. During the breeding season, which aligns with the rainy months, males increase their roaming activity to locate receptive females. Olfactory cues play a key role in mate location, as both sexes rub anal on trees to signal availability and territory. The gestation period in two-toed sloths ranges from 6 to 11.5 months. Typically, a single offspring is born, with twins occurring rarely at rates below 5%. Females reach reproductive maturity at approximately 3 years of age, while males mature between 4 and 5 years. Two-toed sloths are polyestrous, with ovarian cycles averaging 31 to 33 days independent of external factors. This allows for potential 1 to 2 litters per year, though actual frequency remains low due to interbirth intervals of 15 to 16 months. Recent research on Choloepus hoffmanni has utilized non-invasive methods like to characterize estrous cycles, revealing average durations of 15 days with behavioral indicators such as vulvar swelling and discharge during peaks. These studies confirm hormonal and physiological changes tied to reproductive phases, often aligning with seasonal breeding patterns in rainy periods.

Development and longevity

Two-toed sloth neonates are born after a period of 7 to 10 months, weighing approximately 340 to 454 grams and measuring about 25 centimeters in length. These well-developed immediately cling to their mother's , relying on her for transport and protection during the early months of life. Mothers provide exclusive , nursing the young for around one month before occurs, though the infants continue to ride on the mother's back or belly for 6 to 9 months. This prolonged physical attachment fosters a strong mother-young bond, maintained through grooming and shared arboreal movement, while the young begin consuming solid food, such as leaves, shortly after birth. Growth in two-toed sloths is characteristically slow, reflecting their low metabolic rate and energy-conserving . Juveniles reach and adult size—typically 60 to 70 centimeters in body length and 4 to 6 kilograms in weight—by around 3 to 5 years of age, with females maturing slightly earlier than males. Full independence from the mother generally occurs between 10 and 12 months, though young may remain in close association for up to 2 years, learning foraging routes and habitat preferences within the maternal home range. In the wild, two-toed sloths have an estimated lifespan of 12 to 20 years, while individuals in can live up to 31 to 41 years due to protection from predators and consistent availability. Juvenile mortality is notably high in the period immediately following independence, primarily from predation and accidental falls from trees during dispersal or exploration. The lifecycle of two-toed sloths features extended juvenile dispersal, where subadults move short distances—typically tens to hundreds of meters—through forested habitats to establish stable adult territories, avoiding open areas like pastures. Adults maintain territorial stability for much of their lives, with females exhibiting no and sustaining fertility without significant age-related decline, potentially reproducing into their later years.

Conservation

Status and threats

The two-toed sloths, comprising (Choloepus hoffmanni) and (Choloepus didactylus), are both classified as Least Concern on the , with assessments conducted in 2022 for both species, and no changes reported as of 2025. Despite this status, populations exhibit declining trends primarily driven by habitat loss, with no recognized as endangered. The primary threats to two-toed sloths stem from human activities, including extensive for , , and urban expansion, which has resulted in significant range contraction across their Central and South American habitats since the mid-20th century. Hunting for and the pet trade, along with incidental during infrequent ground descents to defecate, further exacerbate mortality rates, particularly in fragmented landscapes. poses an additional risk, as projected temperature increases exceeding 2°C by 2100 could overwhelm their low metabolic rates and limited thermoregulatory capacity, rendering survival untenable in current habitats according to a 2024 PeerJ study on sloth physiology in . Habitat fragmentation from deforestation reduces gene flow between populations, isolating groups and heightening vulnerability, with notable declines observed in Central American subpopulations of C. hoffmanni due to severe degradation. In response to rising illegal trade pressures, , , and proposed listing both Choloepus species in Appendix II at the 2025 CoP20 meeting to regulate international commerce. Their low reproductive rates—one offspring every 15-18 months—amplify these threats, slowing recovery despite evidence of resilience, such as the 2024 documentation of a 820 km southern range extension for C. didactylus into the Brazilian Amazon. Overall, these pressures continue to diminish population viability across their distribution.

Protection and research

Protection efforts for two-toed sloths focus on preservation and regulatory measures to curb exploitation. In , Soberanía National Park serves as a key where (Choloepus hoffmanni) has been recorded, contributing to the species' conservation within intact ecosystems. Anti-poaching laws in Central American range countries, such as and , prohibit the capture and trade of sloths, with enforcement efforts targeting illegal pet trafficking that claims hundreds of individuals annually. Reforestation initiatives, including the planting of sloth-preferred tree species, aim to create biological corridors that reconnect fragmented s and facilitate movement between forest patches. At the international level, a 2025 proposal co-sponsored by , , and seeks to list both C. hoffmanni and Linnaeus's two-toed sloth (C. didactylus) in Appendix II to regulate trade and prevent unsustainable exploitation driven by the pet market. Rehabilitation programs emphasize soft-release protocols to improve post-release survival for rescued individuals. The Sloth Conservation Foundation supports release strategies that include acclimation in enclosures and habitat connectivity enhancements to aid reintegration. A 2023 study in central examined the post-release ecology of 11 rehabilitated C. hoffmanni individuals, which were hand-reared for an average of 727 days, radiomarked, and held in a 500 m² outdoor enclosure for three months before release; monitoring revealed their adaptation to wild foraging and arboreal behaviors in nearby . Recent research advances highlight vulnerabilities and monitoring techniques for two-toed sloths. A 2024 PeerJ study modeled metabolic responses in C. hoffmanni, finding that their low and limited could render survival untenable under projected 2°C warming, particularly at higher altitudes where body temperature stress intensifies. Genetic monitoring using analysis has detected population divergence and human-mediated translocations in Costa Rican sloth populations, underscoring the impacts of on . studies have characterized natal dispersal patterns, showing that juvenile two-toed sloths in human-dominated landscapes travel up to several kilometers but face high mortality risks from roads and predators during movement. Future directions include calls for updated IUCN Red List assessments, as the most recent evaluation for C. hoffmanni dates to 2022 and may not reflect emerging threats like climate impacts. Community education programs in range countries, such as those by the Sloth Conservation Foundation, target local schools to raise awareness of sloth ecology and reduce incidental hunting through initiatives.

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