Gorilla

Gorillas are the largest extant genus of primates. They are ground-dwelling, predominantly herbivorous apes that inhabit the forests of central Africa. Gorillas comprise one eponymous genus that is divided into two species and either four or five subspecies. The DNA of gorillas is highly similar to that of a human, from 95–99% depending on what is counted, and they are the next closest living relatives to humans after the bonobo and common chimpanzee.
Gorillas' natural habitats cover tropical or subtropical forests in Africa. Although their range covers a small percentage of Africa, gorillas cover a wide range of elevations. The mountain gorilla inhabits the Albertine Rift montane cloud forests of the Virunga Volcanoes, ranging in altitude from 2,200–4,300 metres (7,200–14,100 ft). Lowland gorillas live in dense forests and lowland swamps and marshes as low as sea level, with western lowland gorillas living in Central West African countries and eastern lowland gorillas living in the Democratic Republic of the Congo near its border with Rwanda.

Etymology

 

The American physician and missionary Thomas Staughton Savage and naturalist Jeffries Wyman first described the western gorilla (they called it Troglodytes gorilla) in 1847 from specimens obtained in Liberia. The name was derived from Greek Γόριλλαι (Gorillai), meaning "tribe of hairy women", described by Hanno the Navigator, a Carthaginian navigator and possible visitor (circa 480 BC) to the area that later became Sierra Leone.

Evolution and classification

 

The closest relatives of gorillas are chimpanzees and humans, all of the Hominidae having diverged from a common ancestor about 7 million years ago. Human genes differ only 1.6% on average from their corresponding gorilla genes in their sequence, but there is further difference in how many copies each gene has. Until recently there was considered to be a single gorilla species, with three subspecies: the western lowland gorilla, the eastern lowland gorilla and the mountain gorilla. There is now agreement that there are two species with two subspecies each. More recently it has been claimed that a third subspecies exists in one of the species. The separate species and subspecies developed from a single type of gorilla during the Ice Age, when their forest habitats shrank and became isolated from each other.

Primatologists continue to explore the relationships between various gorilla populations. The species and subspecies listed here are the ones upon which most scientists agree.

Taxonomy of genus Gorilla[1]	Phylogeny of superfamily Hominoidea
Genus Gorilla Western gorilla (Gorilla gorilla) Western lowland gorilla (Gorilla gorilla gorilla) Cross River gorilla (Gorilla gorilla diehli) Eastern gorilla (Gorilla beringei) Mountain gorilla (Gorilla beringei beringei) Eastern lowland gorilla (Gorilla beringei graueri)	Hominoidea humans (genus Homo) chimpanzees (genus Pan) gorillas (genus Gorilla) orangutans (genus Pongo) gibbons (family Hylobatidae)

The proposed third subspecies of Gorilla beringei, which has not yet received a trinomen, is the Bwindi population of the mountain gorilla, sometimes called the Bwindi gorilla.
Some variations that distinguish the classifications of gorilla include varying density, size, hair color, length, culture, and facial widths. There are now thought to be over 100,000 western lowland gorillas in the wild, with 4,000 in zoos; eastern lowland gorillas have a population of 4,000 in the wild and 24 in zoos. Mountain gorillas are the most severely endangered, with an estimated population of about 620 left in the wild and none in zoos.

Physical characteristics

A skull of a gorilla

Gorillas move around by knuckle-walking, although they sometimes walk bipedally for short distances while carrying food or in defensive situations. Adult males, also called silverbacks, range in height 1.65–1.75 metres (5 ft 5 in–5 ft 9 in), and in weight 140–200 kg (310–440 lb). Adult females are often half the size of a silverback, averaging about 1.4 metres (4 ft 7 in) tall and 100 kg (220 lb). Occasionally, a silverback of over 1.8 metres (5 ft 11 in) and 230 kg (510 lb) has been recorded in the wild. Obese gorillas in captivity have reached a weight of 270 kg (600 lb). Gorillas have a facial structure which is described as mandibular prognathism, that is, their mandible protrudes farther out than the maxilla. Adult males also have a prominent sagittal crest.

The eastern gorilla is more darkly colored than the western gorilla, with the mountain gorilla being the darkest of all. The mountain gorilla also has the thickest hair. The western lowland gorilla can be brown or grayish with a reddish forehead. In addition, gorillas that live in lowland forests are more slender and agile than the more bulky mountain gorilla. The eastern gorilla also has a longer face and broader chest than the western gorilla.

Studies have shown that gorilla blood is non-reactive to anti-A and anti-B monoclonal antibodies which would, in humans, indicate type O blood. However, due to novel sequences it is different enough to not conform with the human ABO blood group system, which the other great apes fit into. Like humans, gorillas have individual finger prints. Their eye color is dark brown, framed by a black ring around the iris. Similar to humans, the leading cause of death in gorillas is cardiovascular disease.

Behavior and ecology

Young gorilla in tree

Range and habitat

Gorillas have a patchy distribution. The range of the two species is separated by the Congo river and its tributaries. The western gorilla lives in west central Africa while the eastern gorilla lives in east central Africa. Between the species and even within the species, gorillas live in a variety of habitats and elevations. Gorilla habitat ranges from montane forests to swamps. Eastern gorilla inhabit montane and submontane forests between 650–4000 m (2132-13,123 ft). Mountain gorillas live in the montane forests at the higher ends of the elevation range while eastern lowland gorillas live in submotane forests at the lower ends of the elevation range. In addition, eastern lowland gorillas live in montane bamboo forests as well as lowland forests ranging from 600–3308 m (1969-10,853 ft) in elevation. Western gorillas live in both lowland swamp forests and montane forests and live in elevations ranging from sea level to 1600 m (5249 ft). Western lowland gorillas live in swamp and lowland forests ranging up to 1600 m (5249 ft) and Cross River gorillas live in low-lying and submontane forests ranging 150–1600 m (492–5249 ft).

Food and foraging

Gorillas moving in habitat

Gorilla foraging

A gorilla's day is synchronized, divided between rest periods and travel or feeding periods. There are dietary differences between and within species. Mountain gorillas mostly eat foliage such as leaves, stems, pith, and shoots while fruit makes up a very small part of their diet. They primarily eat bamboo. The food that mountain gorillas eat is widely distributed and both individuals and groups do not have to compete with each other. Their home ranges average 3–15 km² (1.16–5.79 mi²), and their movements range around 500 m (0.311 mi) or less on an average day. Despite eating a few species in each habitat, mountain gorillas have a flexible diet and can live in a variety of habitats.
Eastern lowland gorillas have a more diverse diet which varies seasonally. Leaves and pith are commonly eaten but fruits can make up as much as 25% of their diet. Since fruit is less available, lowland gorillas must travel farther each day and have home ranges that vary from 2.7–6.5 km² (1.04 to 2.51 mi²) with day ranges 154–2280 m (0.096–1.42 mi). Eastern lowland gorillas will also eat insects, preferably ants. Western lowland gorillas depend on fruits more than the others and they are more dispersed across their range. They travel even further than the other gorilla subspecies, at 1105 m (0.687 mi) per day on average, and have larger home ranges of 7–14 km² (2.70–5.41 mi²). Western lowland gorillas have less access to terrestrial herbs, although they can access aquatic herbs in some areas. Termites and ants also are also eaten.
Gorillas rarely drink water "because they consume succulent vegetation that is comprised of almost half water as well as morning dew", although both mountain and lowland gorillas have been observed drinking.
One possible predator of gorillas is the leopard. Gorilla remains have been found in leopard scat but it is possible that this may be the result of scavenging. When the group is attacked by humans, leopards, or other gorillas, an individual silverback will protect the group, even at the cost of his own life. George Schaller reported that a "silverback gorilla and a leopard were both found dead from mutually inflicted wounds".

Social structure

Silverback gorilla with one of his females

Gorillas live in groups called troops. Troops tend to be made of one adult male or silverback, multiple adult females and their offspring. However, multi-male troops also exist. Silverbacks are typically more than 12 years of age and named for the distinctive patch of silver hair on their back which comes with maturity. They also have large canine teeth which also come with maturity. Both males and females tend to emigrate from their natal groups. For mountain gorillas, females disperse from their natal troops more than males. Mountain gorillas and western lowland gorillas also commonly transfer to second new groups. Mature males tend to also leave their groups and establish their own troops by attracting emigrating females. However, male mountain gorillas sometimes stay in their natal troops and become subordinate to the silverback. If the silverback dies, these males may be able to become dominant or mate with the females. This behavior has not been observed in eastern lowland gorillas. In a single male group, when the silverback dies, the females and their offspring disperse and find a new troop. Without a silverback to protect them, the infants will likely fall victim to infanticide. Joining a new group is likely to be a tactic against this. However while gorilla troops usually disband after the silverback dies, female eastern lowlands gorillas and their offspring have been recorded staying together until a new silverback transfers into the group. This likely serves as protection from leopards. All male troops have also been recorded.

Silverback gorilla

The silverback is the center of the troop's attention, making all the decisions, mediating conflicts, determining the movements of the group, leading the others to feeding sites and taking responsibility for the safety and well-being of the troop. Younger males subordinate to the silverback, known as blackbacks, may serve as backup protection. Blackbacks are aged between 8 and 12 years of age and lack the silver back hair. The bond a silverback has with his females forms the core of gorilla social life. Bonds between them are maintained by grooming and stay close together. Females form strong relationships with males to gain mating opportunities and protection from predators and infanticidal outside males. However aggressive behaviors between males and females do occur but rarely lead to serious injury. Relationships between females may vary. Maternally related females in a troop tend to be friendly towards each other and associate closely. Otherwise, females have few friendly encounters and commonly act aggressively towards each other. Females may fight for social access to males and a male may intervene. Male gorillas have weak social bonds, particularly in multi-male groups with apparent dominance hierarchies and strong competition for mates. However, males in all-male groups tend to have friendly interactions and socialize through play, grooming and staying together, and occasionally they even engage in homosexual interactions.

Nesting

Gorilla night nest constructed in a tree.

Gorillas construct nests for daytime and night use. Nests tend to be simple aggregations of branches and leaves about 2 to 5 feet (0.61 to 1.5 m) in diameter and are constructed by individuals. Gorillas, unlike chimpanzees or orangutans, tend to sleep in nests on the ground. The young nest with the mother but construct nests after three years of age, initially close to that of their mother. Gorilla nests are distributed arbitrarily and use of tree species for site and construction appears to be opportunistic. Nest building by great apes is now considered to be not just animal architecture but as an important instance of tool use.

Reproduction and parenting

Young gorilla riding on mother

Females mature at 10–12 years (earlier in captivity); males at 11–13 years. A female’s first ovulatory cycle occurs when she is six years of age and is followed by a two year long period of adolescent infertility. The estrous cycle last 30–33 days with outward ovulation signs subtle compared to that of chimpanzees. The gestation period lasts 8.5 months. Female mountain gorillas first give birth at 10 years of age and have four year interbirth intervals. Males can be fertile before reaching adulthood. Gorillas mate year round.
Females will purse their lips and slowly approach a male while and make eye contact. This serves to urge the male to mount her. If the male does not respond, then she will try to attract his attention by reaching towards him or slapping the ground. In multi-male groups, solicitation indicates female preference. However females can be forced to mate with multiple males. Males incite copulation by approaching a female and displaying at her or touching her and giving a "train grunt". Recently, gorillas have been observed engaging in face-to-face sex, a trait that was once considered unique to humans and the bonobo.

Mother gorilla with 10-day-old infant

Gorilla infants are vulnerable and dependant and thus mothers, their primary caregivers, are important to their survival. Male gorillas are not active in caring for the young. However they do play a role in socializing them to other youngsters. The silverback has a largely supportive relationship with the infants in his troop and shields them from aggression within the group. Infants remain in contact with their mothers for the first five months and mothers stay near the silverback for protection. Infants will suckle at least once per hour and will sleep with their mothers in the same nest.
Infants begin to break contact with their mothers after five months but only for brief period each time. By 12 months, infants move up to five meters (16.4 ft) from their mothers. At around 18–21 months, the distance between mother and offspring increases and they regularly spend time away from each other. In addition, nursing decreases to once every two hours. Infants spend only half of their time with their mothers by 30 months. They enter their juvenile period at their third year and this lasts until their sixth year. At this time, gorillas are weaned and they sleep in a separate nest from their mothers. After their offspring are weaned, females begin to ovulate and soon become pregnant again. The presence of play partners, including the silverback, minimize conflicts in weaning between mother and offspring.

Lifespan

A gorilla's lifespan is between 35–40 years, although zoo gorillas may live for 50 years and more. Dallas Zoo's Jenny was the oldest living gorilla in captivity until 2008 when she died at the age of 55. Now it is Colo - on December 22, 2011 she celebrated her 55th birthday in Columbus Zoo.

Communication

Twenty-five distinct vocalizations are recognized, many of which are used primarily for group communication within dense vegetation. Sounds classified as grunts and barks are heard most frequently while traveling, and indicate the whereabouts of individual group members. They may also be used during social interactions when discipline is required. Screams and roars signal alarm or warning, and are produced most often by silverbacks. Deep, rumbling belches suggest contentment and are heard frequently during feeding and resting periods. They are the most common form of intragroup communication. Severe aggression is rare in stable groups, but when two mountain gorilla groups meet, the two silverbacks can sometimes engage in a fight to the death, using their canines to cause deep, gaping injuries. The entire sequence has nine steps: (1) progressively quickening hooting, (2) symbolic feeding, (3) rising bipedally, (4) throwing vegetation, (5) chest-beating with cupped hands, (6) one leg kick, (7) sideways running, two-legged to four-legged, (8) slapping and tearing vegetation, and (9) thumping the ground with palms to end display.

Intelligence

Gorillas are considered highly intelligent. A few individuals in captivity, such as Koko, have been taught a subset of sign language. Like the other great apes, gorillas can laugh, grieve, have "rich emotional lives," develop strong family bonds, can make and use tools, and can think about the past and future. Some researchers believe that gorillas have spiritual feelings or religious sentiments. Gorillas have been shown to have cultures in different areas revolving around different methods of food preparation, and gorillas will show individual color preferences.

Tool use

A female gorilla exhibiting tool use by using a tree trunk as a support whilst fishing herbs.

The following observations were made by a team led by Thomas Breuer of the Wildlife Conservation Society in September 2005. Gorillas are now known to use tools in the wild. A female gorilla in the Nouabalé-Ndoki National Park in the Republic of Congo was recorded using a stick as if to gauge the depth of water whilst crossing a swamp. A second female was seen using a tree stump as a bridge and also as a support whilst fishing in the swamp. This means that all of the great apes are now known to use tools.
In September 2005, a two and a half year old gorilla in the Republic of Congo was discovered using rocks to smash open palm nuts inside a game sanctuary. While this was the first such observation for a gorilla, over 40 years previously chimpanzees had been seen using tools in the wild 'fishing' for termites. Great apes are endowed with a semi-precision grip, and have been able to use both simple tools and even weapons, by improvising a club from a convenient fallen branch.

Interactions with humans

 

Studies

The word "gorilla" comes from the history of Hanno the Navigator, a Carthaginian explorer on an expedition on the west African coast. They encountered "a savage people, the greater part of whom were women, whose bodies were hairy, and who our interpreters called Gorillae". The word was then later used as the species name, though it is unknown whether what these ancient Carthaginians encountered were truly gorillas, another species of ape or monkeys, or humans.
American physician and missionary Thomas Staughton Savage obtained the first specimens (the skull and other bones) during his time in Liberia in Africa. The first scientific description of gorillas dates back to an article by Savage and the naturalist Jeffries Wyman in 1847 in Proceedings of the Boston Society of Natural History, where Troglodytes gorilla is described, now known as the Western Gorilla. Other species of gorilla are described in the next couple of years.
Explorer Paul du Chaillu was the first westerner to see a live gorilla during his travel through western equatorial Africa from 1856 to 1859. He brought dead specimens to the UK in 1861.
The first systematic study was not conducted until the 1920s, when Carl Akeley of the American Museum of Natural History traveled to Africa to hunt for an animal to be shot and stuffed. On his first trip he was accompanied by his friends Mary Bradley, a mystery writer, and her husband. After their trip, Mary Bradley wrote On the Gorilla Trail. She later became an advocate for the conservation of gorillas and wrote several more books (mainly for children). In the late 1920s and early 1930s, Robert Yerkes and his wife Ava helped further the study of gorillas when they sent Harold Bigham to Africa. Yerkes also wrote a book in 1929 about the great apes.

Drawing of French explorer Paul du Chaillu at close quarters with a gorilla

After World War II, George Schaller was one of the first researchers to go into the field and study primates. In 1959, he conducted a systematic study of the mountain gorilla in the wild and published his work. Years later, at the behest of Louis Leakey and the National Geographic, Dian Fossey conducted a much longer and more comprehensive study of the mountain gorilla. It was not until she published her work that many misconceptions and myths about gorillas were finally disproved, including the myth that gorillas are violent.

Conservation status

The eastern gorilla is listed as endangered on the IUCN Red List, with the mountain gorilla listed as Critically Endangered. The western gorilla and its subspecies are also listed as Critically Endangered. Threats to gorilla survival include habitat destruction and poaching for the bushmeat trade. In 2004, a population of several hundred gorillas in the Odzala National Park, Republic of Congo was essentially wiped out by the Ebola virus. A 2006 study published in Science concluded that more than 5,000 gorillas may have died in recent outbreaks of the Ebola virus in central Africa. The researchers indicated that in conjunction with commercial hunting of these apes, the virus creates "a recipe for rapid ecological extinction." Conservation efforts include the Great Ape Survival Project, a partnership between the United Nations Environment Programme and the UNESCO, and also an international treaty, the Agreement on the Conservation of Gorillas and Their Habitats, concluded under UNEP-administered Convention on Migratory Species. The Gorilla Agreement is the first legally binding instrument exclusively targeting Gorilla conservation and came into effect on 1 June 2008.

Genome sequencing

The gorilla became the next last great ape genus to have its genome sequenced. This has given scientists further insight into the evolution and origin of humans. Despite the chimpanzees being the closest extant relatives of humans, it was found that 15% of the human genome is more like that of the gorilla. In addition 30% of the gorilla genome "is closer to human or chimpanzee than the latter are to each other; this is rarer around coding genes, indicating pervasive selection throughout great ape evolution, and has functional consequences in gene expression." Analysis of the gorilla genome has cast doubt on the idea that the rapid evolution of hearing genes gave rise to language in humans as it also occurred in gorillas.

Cultural references

Since they came to the attention of western society in the 1860s, gorillas have been a recurring element of many aspects of popular culture and media. For example, gorillas have featured prominently in monstrous fantasy films such as King Kong, and pulp fiction such as the stories of Tarzan and Conan the Barbarian have featured gorillas as physical opponents to the titular protagonists.

Giant Otter

The giant otter (Pteronura brasiliensis) is a South American carnivorous mammal. It is the longest member of the Mustelidae, or weasel family, a globally successful group of predators. Unusual for a mustelid, the giant otter is a social species, with family groups typically supporting three to eight members. The groups are centered on a dominant breeding pair and are extremely cohesive and cooperative. Although generally peaceful, the species is territorial, and aggression has been observed between groups. The giant otter is diurnal, being active exclusively during daylight hours. It is the noisiest otter species, and distinct vocalizations have been documented that indicate alarm, aggressiveness, and reassurance. The giant otter ranges across north-central South America; it lives mostly in and along the Amazon River and in the Pantanal.
Its distribution has been greatly reduced and is now discontinuous. Decades of poaching for its velvety pelt, peaking in the 1950s and 1960s, hugely diminished population numbers. The species was listed as endangered in 1999 and wild population estimates are typically below 5,000. The Guianas are one of the last real strongholds for the species, which also enjoys modest numbers - and significant protection - in the Peruvian Amazonian basin. It is one of the most endangered mammal species in the neotropics. Habitat degradation and loss is the greatest current threat. The giant otter is also rare in captivity; in 2003, only 60 animals were being held.
The giant otter shows a variety of adaptations suitable to an amphibious lifestyle, including exceptionally dense fur, a wing-like tail, and webbed feet. The species prefers freshwater rivers and streams, which are usually seasonally flooded, and may also take to freshwater lakes and springs. It constructs extensive campsites close to feeding areas, clearing large amounts of vegetation. The giant otter largely subsists on a diet of fish, particularly characins and catfish, and may also eat crabs. It has no serious natural predators other than humans, although it must compete with other species, including the neotropical otter and caiman species, for food resources.

Naming

 

The giant otter has a handful of other names. River wolf (Spanish: lobo de río) and water dog (Spanish: perro de agua) are used occasionally, though the latter has many other meanings) and may have been more common in the reports of explorers in the 19th and early 20th centuries. All three names are in use in Spanish and Portuguese, with a number of regional variations. "Giant otter" translates as nutria gigante and lontra gigante in Spanish and Portuguese, respectively; a fourth name, ariraí or ariranha is also in use in South America. Among the Achuar people, they are known as wankanim, and among the Sanumá as hadami. The genus name, Pteronura, is derived from the Ancient Greek words pteron/πτερον (feather or wing) and ura/ουρά (tail), a reference to its distinctive, wing-like tail.

Taxonomy and evolution

 

Giant otter head from the Museu Paraense Emílio Goeldi research institute

The otters form the Lutrinae subfamily within the mustelids and the giant otter is the only member of the genus Pteronura. Two subspecies are currently recognized by the canonical Mammal Species of the World, P. b. brasiliensis and P. b. paraguensis. Incorrect descriptions of the species have led to multiple synonyms (the latter subspecies is often P. b. paranensis in the literature). P. b. brasiliensis is distributed across the north of the giant otter range, including the Orinoco, Amazon, and Guianas river systems; to the south, P. b. paraguensis has been suggested in Paraguay, Uruguay, southern Brazil, and northern Argentina, although it may be extinct in the last three of these four. The World Conservation Union (IUCN) considers the species' presence in Argentina and Uruguay uncertain. In the former, investigation has shown thinly distributed population remnants. P. b. paraguensis is supposedly smaller and more gregarious, with different dentition and skull morphology. Carter and Rosas, however, rejected the subspecific division in 1997, noting the classification had only been validated once, in 1968, and the P. b. paraguensis type specimen was very similar to P. b. brasiliensis. Biologist Nicole Duplaix calls the division of "doubtful value".
An extinct genus, Satherium, is believed to be ancestral to the present species, having migrated to the New World during the Pliocene or early Pleistocene. The giant otter shares the South American continent with three of the four members of the Lontra genus of otters: the neotropical river otter, the southern river otter, and the marine otter. It seems to have evolved independently of Lontra in South America, despite the overlap. The smooth-coated otter (Lutrogale perspicillata) of Asia may be its closest extant relative; similar behaviour, vocalizations, and skull morphology have been noted. Both species also show strong pair bonding and paternal engagement in rearing cubs.
Phylogenetic analysis by Koepfli and Wayne in 1998 found the giant otter has the highest divergence sequences within the otter subfamily, forming a distinct clade that split away 10 to 14 million years ago. They noted the species may be the basal divergence among the otters or fall outside of them altogether, having split even before other mustelids, such as the ermine, polecat, and mink. Later gene sequencing research on the mustelids, from 2005, places the divergence of the giant otter somewhat later, between five and 11 million years ago; the corresponding phylogenetic tree locates the Lontra divergence first among otter genera, and Pteronura second, although divergence ranges overlap.

Biology and behavior

 

The giant otter is large, gregarious, and diurnal (active through the day). Early travellers' reports describe noisy groups surrounding explorers' boats, but little scientific information was available on the species until Duplaix's groundbreaking work in the late 1970s. Concern over this endangered species has since generated a body of research.

Physical characteristics

A wild giant otter "periscoping" in Cantão State Park in Brazil, showing its identifying throat 

marks

Skull seen from the side
Short-snouted as usual in mustelids, it has a pronounced sagittal crest in this species, allowing for a very powerful bite

The giant otter is clearly distinguished from other otters by morphological and behavioral characteristics. It has the greatest body length of any species in the mustelid family, although the sea otter may be heavier. Males are between 1.5 and 1.7 m (4.9 and 5.6 ft) in length from head to tail and females between 1 and 1.5 m (3.3 and 4.9 ft). The animal's well-muscled tail can add a further 70 cm (28 in) to the total body length. Early reports of skins and living animals suggested exceptionally large males of up to 2.4 m (7.9 ft); intensive hunting likely reduced the occurrence of such massive specimens. Weights are between 26 and 32 kg (57 and 71 lb) for males and 22 and 26 kg (49 and 57 lb) for females. The giant otter has the shortest fur of all otter species; it is typically chocolate brown, but may be reddish or fawn, and appears nearly black when wet. The fur is extremely dense, so much so that water cannot penetrate to the skin. Guard hairs trap water and keep the inner fur dry; the guard hairs are approximately 8 millimeters (one-third of an inch) in length, about twice as long as the fur of the inner coat. Its velvety feel makes the animal highly sought after by fur traders and has contributed to its decline. Unique markings of white or cream fur color the throat and under the chin, allow individuals to be identified from birth. Giant otters use these marks to recognize one another, and upon meeting other otters, they engage in a behavior known as "periscoping", displaying their throats and upper chests to each other.
Giant otter muzzles are short and sloping and give the head a ball-shaped appearance. The ears are small and rounded. The nose (or rhinarium) is completely covered in fur, with only the two slit-like nostrils visible. The giant otter's highly sensitive whiskers (vibrissae) allow the animal to track changes in water pressure and currents, which aids in detecting prey. The legs are short and stubby and end in large webbed feet tipped with sharp claws. Well suited for an aquatic life, it can close its ears and nose while underwater.
At the time of Carter and Rosas' writing, vision had not been directly studied, but field observations show the animal primarily hunts by sight; above water, it is able to recognize observers at great distances. The fact that it is exclusively active during the day further suggests its eyesight should be strong, to aid in hunting and predator avoidance. In other otter species, vision is generally normal or slightly myopic, both on land and in water. The giant otter's hearing is acute and its sense of smell excellent.

Vocalizations

The giant otter is an especially noisy animal, with a complex repertoire of vocalizations. All otters produce vocalizations, but by frequency and volume, the giant otter may be the most vocal. Duplaix identified 9 distinct sounds, with further subdivisions possible, depending on context. Quick HAH! barks or explosive snorts suggest immediate interest and possible danger. A wavering scream may be used in bluff charges against intruders, while a low growl is used for aggressive warning. Hums and coos are more reassuring within the group. Whistles may be used as advance warning of nonhostile intent between groups, although evidence is limited. Newborn pups squeak to elicit attention, while older young whine and wail when they begin to participate in group activities.

Social structure

The giant otter is a highly social animal and lives in extended family groups. Group sizes are anywhere from two to 20 members, but likely average between three and eight. (Larger figures may reflect two or three family groups temporarily feeding together.) The groups are strongly cohesive: the otters sleep, play, travel, and feed together.

Giant otters leave a pool together at the Philadelphia Zoo. The species is extremely social, a rarity amongst mustelids, and family groups are cohesive.

Group members share roles, structured around the dominant breeding pair. The species is territorial, with groups marking their ranges with latrines, gland secretions, and vocalizations. At least one case of a change in alpha relationship has been reported, with a new male taking over the role; the mechanics of the transition were not determined. Duplaix suggests a division between "residents", who are established within groups and territories, and nomadic and solitary "transients"; the categories do not seem rigid, and both may be a normal part of the giant otter life cycle. One tentative theory for the development of sociality in mustelids is that locally abundant, but unpredictably dispersed, prey causes groups to form.
Aggression within the species ("intraspecific" conflict) has been documented. Defense against intruding animals appears to be cooperative: while adult males typically lead in aggressive encounters, cases of alpha females guarding groups have been reported. One fight was directly observed in the Brazilian Pantanal in which three animals violently engaged a single individual near a range boundary. In another instance in Brazil, a carcass was found with clear indications of violent assault by other otters, including bites to the snout and genitals, an attack pattern similar to that exhibited by captive animals. While not rare among large predators in general, intraspecific aggression is uncommon among otter species; Ribas and Mourão suggest a correlation to the animal's sociability, which is also rare among other otters. A capacity for aggressive behavior should not be overstated with the giant otter. Researchers emphasize that even between groups, conflict avoidance is generally adopted. Within groups, the animals are extremely peaceful and cooperative. Group hierarchies are not rigid and the animals easily share roles.

Reproduction and life cycle

A giant otter den dug on a lake shore at Cantão State Park - the newly dug white sand is a sign of recent activity at this den.

Giant otters build dens, which are holes dug into riverbanks, usually with multiple entrances and multiple chambers inside. They give birth within these dens during the dry season. In Cantão State Park, otters dig their reproductive dens on the shores of oxbow lakes starting around July, when waters are already quite low. They give birth between August and September, and the young pups emerge for the first time in October and November, which are the months of lowest water and fish concentrations in the dwindling lakes and channels are at their peak. This makes it easier for the adults to catch enough fish for the growing young, and for the pups to learn how to catch fish. The entire group, including nonreproductive adults, which are usually older siblings to that year's pups, collaborates to catch enough fish for the young.
Details of giant otter reproduction and life cycle are scarce, and captive animals have provided much of the information. Females appear to give birth year round, although in the wild, births may peak during the dry season. The estrous cycle is 21 days, with females receptive to sexual advances between three and 10 days. Study of captive specimens has found only males initiate copulation. At Tierpark Hagenbeck in Germany, long-term pair bonding and individualized mate selection were seen, with copulation most frequently taking place in water. Females have a gestation period of 65 to 70 days, giving birth to one to five pups, with an average of two. Research over five years on a breeding pair at the Cali Zoo in Colombia found the average interval between litters was six to seven months, but as short as 77 days when the previous litter did not survive. Other sources have found greater intervals, with as long as 21 to 33 months suggested for otters in the wild.

Captive giant otters have contributed greatly to scientific knowledge of the species by providing readily available subjects for research on the species' reproduction and life cycle.

Mothers give birth to furred and blind cubs in an underground den near the river shore and fishing sites. Males actively participate in rearing cubs and family cohesion is strong; older, juvenile siblings also participate in rearing, although in the weeks immediately after birth, they may temporarily leave the group. Pups open their eyes in their fourth week, begin walking in their fifth, and are able to swim confidently between 12 and 14 weeks old. They are weaned by 9 months and begin hunting successfully soon after. The animal reaches sexual maturity at about two years of age and both male and female pups leave the group permanently after two to three years. They then search for new territory to begin a family of their own.
The giant otter is very sensitive to human activity when rearing its young. No institution, for example, has successfully raised giant otter cubs unless parents were provided sufficient privacy measures; the stress caused by human visual and acoustic interference can lead to neglect, abuse and infanticide, as well as decreased lactation. In the wild, it has been suggested, although not systematically confirmed, that tourists cause similar stresses: disrupted lactation and denning, reduced hunting, and habitat abandonment are all risks. This sensitivity is matched by a strong protectiveness towards the young. All group members may aggressively charge intruders, including boats with humans in them.
The longest documented giant otter lifespan in the wild is eight years. In captivity, this may increase to 17, with an unconfirmed record of 19. The animal is susceptible to a variety of diseases, including canine parvovirus. Parasites, such as the larvae of flies and a variety of intestinal worms, also afflict the giant otter. Other causes of death include accidents, gastroenteritis, infanticide, and epileptic seizures.

Hunting and diet

A captive giant otter, when feeding, grasps prey in its forepaws and begins eating immediately, at the head.

The giant otter is an apex predator, and its population status reflects the overall health of riverine ecosystems. It feeds mainly on fish, including cichlids, characins (such as piranha), and catfish. One full-year study of giant otter scats in Amazonian Brazil found fish present in all fecal samples. Fish from the order Perciformes, particularly cichlids, were seen in 97% of scats, and Characiformes, such as characins, in 86%. Fish remains were of medium-sized species that seem to prefer relatively shallow water, to the advantage of the probably visually oriented giant otter. Prey species found were also sedentary, generally swimming only short distances, which may aid the giant otter in predation. The giant otter seems to be opportunistic, taking whatever species are most locally abundant. If fish are unavailable, it will also take crabs, snakes, and even small caimans and anacondas.
The species can hunt singly, in pairs, and in groups, relying on sharp eyesight to locate prey. In some cases, supposed cooperative hunting may be incidental, a result of group members fishing individually in close proximity; truly coordinated hunting may only occur where the prey cannot be taken by a single giant otter, such as with anacondas and the black caiman. The giant otter seems to prefer prey fish that are generally immobile on river bottoms in clear water. Prey chase is rapid and tumultuous, with lunges and twists through the shallows and few missed targets. The otter can attack from both above and below, swiveling at the last instant to clamp the prey in its jaws. Giant otters catch their own food and consume it immediately; they grasp the fish firmly between the forepaws and begin eating noisily at the head. Carter and Rosas have found captive adult animals consume around 10% of their body weight daily—about 3 kilograms (7 lb), in keeping with findings in the wild.

Ecology

 

Habitat

The species is amphibious, although primarily terrestrial. It is found in freshwater rivers and streams, which are generally seasonally flooded. Other water habitats include freshwater springs and permanent freshwater lakes. Four specific vegetation types were found on one important creek in Suriname: riverbank high forest, floodable mixed marsh and high swamp forest, floodable low marsh forest, and grass islands and floating meadows within open areas of the creek itself. Duplaix identified two critical factors in habitat selection: food abundance, which appears to positively correlate to shallow water, and low sloping banks with good cover and easy access to preferred water types. The giant otter seems to choose clear, black waters with rocky or sandy bottoms over silty, saline, and white waters.

A group of four giant otters emerging from the water to patrol a campsite on the riverbank at Cantão State Park

Areas adjacent to rivers are used for the construction dens, campsites, and latrines. Giant otters clear significant amounts of vegetation in constructing their campsites. One report suggests maximum areas 28 m (92 ft) long and 15 m (49 ft) wide, well-marked by scent glands, urine, and feces to signal territory. Carter and Rosas found average areas a third this size. Communal latrines are adopted adjacent to the campsites, and dens with a handful of entrances are dug, typically under root systems or fallen trees. One report found between three and eight campsites, clustered around feeding areas. In seasonally flooded areas, the giant otter may abandon campsites during the wet season, dispersing to flooded forests in search of prey. Preferred locations may be adopted perennially, often on high ground. These can become quite extensive, including "backdoor" exits into forests and swamps, away from the water. Not every site is visited or marked daily, but all are usually patrolled, often by a pair of otters in the morning.
Research generally takes place in the dry season and an understanding of the species' overall habitat use remains partial. Dry season range size analysis of three otter groups in Ecuador found areas between 0.45 and 2.79 square kilometres (0.17 and 1.08 sq mi). Habitat requirements and availability were presumed to be dramatically different in the rainy season: range sizes of 1.98 to as much as 19.55 square kilometres (0.76 to 7.55 sq mi) were estimated for the groups. Other researchers suggest approximately 7 square kilometres (2.7 sq mi) and note a strong inverse correlation between sociality and home range size; the highly social giant otter has smaller home range sizes than would be expected for a species of its mass. Population densities varied with a high of 1.2 /km² (3.1 /sq mi) reported in Suriname and with a low of 0.154 /km² (0.40 /sq mi) found in Guyana.

Predation and competition

Characins such as piranha species are prey for the giant otter, but these aggressive fish may also pose a danger. Duplaix speculated that piranhas may attack giant otters.

Adult giant otters have no serious natural enemies, beyond humans. "Possible and occasional" predation by the jaguar, cougar, and anacondas has been suggested by Duplaix, but based on historical reports, not direct observation. Pups are more vulnerable, and may be taken by the black caiman and other large predators, although adults are constantly mindful of stray young. The spectacled caiman is another potential competitor, but Duplaix found no conflict with the species in Suriname. When in the water, the giant otter faces danger from animals not strictly preying upon it: the electric eel and stingrays are potentially deadly if stumbled upon, and piranha may be capable of at least taking bites out of a giant otter, as evidenced by scarring on individuals.
Even if without direct predation, the giant otter must still compete with other predators for food resources. Duplaix documented interaction with the neotropical otter. While the two species are sympatric (with overlapping ranges) during certain seasons, there appeared to be no serious conflict. The smaller neotropical otter is far more shy, less noisy, and less social; at about a third the weight of the giant otter, it is more vulnerable to predation, hence, a lack of conspicuousness is to its advantage. The neotropical otter is active during twilight and darkness, reducing the likelihood of conflict with the diurnal giant otter. Its smaller prey, different denning habits, and different preferred water types also reduce interaction.
Other species that prey upon similar food resources include the caimans and large fish that are themselves piscivores. Gymnotids, such as the electric eel, and the large silurid catfish are among aquatic competitors. Two river dolphins, the tucuxi and boto, might potentially compete with the giant otter, but different spatial use and dietary preferences suggest minimal overlap.

Conservation status

 

The IUCN listed the giant otter as "endangered" in 1999; it had been considered "vulnerable" under all previous listings from 1982 when sufficient data had first become available. It is regulated internationally under Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES): all trade in specimens and parts is illegal.

Threats

The animal faces a variety of critical threats. Poaching has long been a problem. Statistics show between 1959 and 1969 Amazonian Brazil alone accounted for 1,000 to 3,000 pelts annually. The species was so thoroughly decimated, the number dropped to just 12 in 1971. The implementation of CITES in 1973 finally brought about significant hunting reductions, although demand did not disappear entirely: in the 1980s, pelt prices were as high as US$250 on the European market. The threat has been exacerbated by the otters' relative fearlessness and tendency to approach human beings. They are extremely easy to hunt, being active through the day and highly inquisitive. The animal's relatively late sexual maturity and complex social life makes hunting especially disastrous.
More recently, habitat destruction and degradation have become the principal dangers, and a further reduction of 50% is expected in giant otter numbers within the 20 years after 2004 (about the span of three generations of giant otters). Typically, loggers first move into rainforest, clearing the vegetation along riverbanks. Farmers follow, creating depleted soil and disrupted habitats. As human activity expands, giant otter home ranges become increasingly isolated. Subadults leaving in search of new territory find it impossible to set up family groups. Specific threats from human industry include unsustainable mahogany logging in parts of the giant otter range, and concentrations of mercury in its diet of fish, a byproduct of gold mining. Water pollution from mining, fossil fuel extraction, and agriculture is a serious danger; concentrations of pesticies and other chemicals are magnified at each step in the food chain, and can poison top predators such as the giant otter.
Other threats to the giant otter include conflict with fishermen, who often view the species as a nuisance. Ecotourism also presents challenges: while it raises money and awareness for the animals, by its nature it also increases human effect on the species, both through associated development and direct disturbances in the field. A number of restrictions on land use and human intrusion are required to properly maintain wild populations. Schenck et al., who undertook extensive fieldwork in Peru in the 1990s, suggest specific "no-go" zones where the species is most frequently observed, offset by observation towers and platforms to allow viewing. Limits on the number of tourists at any one time, fishing prohibitions, and a minimum safe distance of 50 metres (164 ft) are proposed to offer further protection.

Distribution and population

The giant otter has lost as much as 80% of its South American range. While still present in a number of north-central countries, giant otter populations are under considerable stress. The IUCN lists Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Peru, Suriname, and Venezuela as current range countries. Given local extinctions, the species' range has become discontinuous. Total population numbers are difficult to estimate. An IUCN study in 2006 suggested 1,000 to 5,000 otters remain. Populations in Bolivia were once widespread but the country became a "black spot" on distribution maps after poaching between the 1940s and 1970s; a relatively healthy, but still small, population of 350 was estimated in the country in 2002. The species has likely been extirpated from southern Brazil, but in the west of the country, decreased hunting pressure in the critical Pantanal has led to very successful recolonization; an estimate suggests 1,000 or more animals in the region.

The Guianas are the last real stronghold of the giant otter. Suriname retains extensive forest cover and many protected areas; it is pictured above. Guyana is immediately to the west and French Guiana is immediately to the east.

In 2006, most of this species lived in the Brazilian Amazon and its bordering areas. A significant population lives in the wetlands of the central Araguaia River, and in particular within Cantão State Park, which, with its 843 oxbow lakes and extensive flooded forests and marshlands, is one of the best habitat patches for this species in Brazil.
Suriname still has significant forest cover and an extensive system of protected areas, much of which protects the giant otter. Duplaix returned to the country in 2000 and found the giant otter still present on the Kaburi Creek, a "jewel" of biodiversity, although increased human presence and land use suggests, sooner or later, the species may not be able to find suitable habitat for campsites. In a report for World Wildlife Fund in 2002, Duplaix was emphatic about the importance of Suriname and the other Guianas:

“

The three Guianas remain the last stronghold of giant otters in South America, with pristine giant otter habitat on some rivers and good giant otter densities overall—still, but for how long? The survival of the giant otter populations in the Guianas is essential to the survival of this endangered species in South America.

”

Other countries have taken a lead in designating protected areas in South America. In 2004, Peru created one of the largest conservation areas in the world, Alto Purús National Park, with an area similar in size to Belgium. The park harbors many endangered plants and animals, including the giant otter, and holds the world record for mammal diversity. Bolivia designated wetlands larger than the size of Switzerland as a freshwater protected area in 2001; these are also home to the giant otter.

Interactions with indigenous peoples

 

Throughout its range, the giant otter interacts with indigenous groups, who often practice traditional hunting and fishing. A study of five indigenous communities in Colombia suggests native attitudes toward the animal are a threat: the otters are often viewed as a nuisance that interferes with fishing, and are sometimes killed. Even when told of the importance of the species to ecosystems and the danger of extinction, interviewees showed little interest in continuing to coexist with the species. Schoolchildren, however, had a more positive impression of the animal.
In Suriname, the giant otter is not a traditional prey species for human hunters, which affords some protection. (One researcher has suggested the giant otter is hunted only in desperation due to its horrible taste.) The animal sometimes drowns in nets set across rivers and machete attacks by fishermen have been noted, according to Duplaix, but "tolerance is the rule" in Suriname. One difference in behavior was seen in the country in 2002: the normally inquisitive giant otters showed "active avoidance behavior with visible panic" when boats appeared. Logging, hunting, and pup seizure may have led groups to be far more wary of human activity.
Local people sometimes take pups for the exotic pet trade or as pets for themselves, but the animal rapidly grows to become unmanageable. Duplaix relates the story of an Arawak Indian who took two pups from their parents. While revealing of the affection held for the animals, the seizure was a profound blow to the breeding pair, which went on to lose their territory to competitors.
The species has also appeared in the folklore of the region. It plays an important role in the mythology of the Achuar people, where giant otters are seen as a form of the tsunki, or water spirits: they are a sort of "water people" who feed on fish. They appear in a fish poisoning legend where they assist a man who has wasted his sexual energy, creating the anacondas of the world from his distressed and extended genitals. The Bororo have a legend on the origin of tobacco smoking: those who used the leaf improperly by swallowing it were punished by being transformed into giant otters; the Bororo also associate the giant otter with fish and with fire. A Ticuna legend has it that the giant otter exchanged places with the jaguar: the story says jaguar formerly lived in the water and the giant otter came to the land only to eat. The indigenous Kichwa peoples from Amazonian Peru believed in a world of water where Yaku runa reigned as mother of the water and was charged with caring for fish and animals. Giant otters served as Yaku runa's canoes.