The Binturong – Arctictis binturong (Raffles, 1821)
Arctictis binturong is a species from the family viverridae, which also includes the civets, genets and mongoose. There are around 35 species in total in this family, all native to the Old World tropics, nearly all of Africa, Madagascar and the Iberian Peninsula. Viverrids are amongst the primitive families of the order Carnivora, with their bone structure having changed little from 50 million years ago. Arctictis binturong is the largest of the viverrids and the most specialised.
The binturong is distributed through Vietnam, Malaysia, Indonesia and Palawan Island. Its habitat is in the trees of the rainforests within these countries. It is known as the Asian Bearcat, or simply the Bearcat, though it is neither bear not car, and the origin of this name is unknown. The binturong remains somewhat of a mystery and their natural behaviour and ecology have not been studied. Binturong are often kept as pets, due to their appearance and general good nature, though they can be aggressive when cornered and have a powerful bite at their disposal. Many zoos house them as exhibits, therefore more is known about their behaviour in captivity. There are currently six known subspecies of Arctictis binturong, and the population of the Palawan Binturong, Arctictis binturong whitei, is currently under threat due to habitat destruction and poaching of the animal for it medicinal uses and its fur. Other populations are presently classed as ‘least concern’ by IUCN.
Binturongs have distinctive physical characteristics. They show sexual dimorphism with the female being on average 20% bigger than the male when maturity is reached. The fur of the animal is in the majority black at the base and in some areas of the body varying proportions of the hair shaft will be ‘tipped’ with different colours; white, gold or brown being most common. Individual colours and patterns will vary, though these different colours are generally displayed in similar areas of the body between individuals, being the tips of the ears, eyebrows, along the backs and sides of the forelegs and on the thighs. Binturong are hard to spot in the wild as they are very well camouflaged within their surroundings.
The tail of the binturong is fully prehensile, which is a specialisation for the arboreal lifestyle of the animal. It is one of only two species of carnivorans that have such a tail, the other being the kinkajou, Potos flavus, which is a rainforest mammal native to South America. Animals with prehensile tails seem to be more common the South American forests and it is thought this could be due to the higher density of trees within these jungles. Forests of Africa and South East Asia tend to be less dense and gliding animals appear to be more common in these areas. The binturong are the only animals of the Old World with a fully prehensile tail. Others with such tails sharing habitat with the binturong are animals from the primate family. This adaptation to the arboreal life style presenting across different families of animals is an example of convergent evolution.
The binturong is poorly adapted to terrestrial living and awkwardly ambles from side to side when walking here, similar to the gait of bears. It spends the majority of its time high up in the canopy. In addition to its prehensile tail, the binturong has other adaptations that enable it to climb with ease. They have sharp claws on both front and hind feet, which are sheathed and semi-retractable, so the animal is able to have control over how much of its curved claw it embeds in any given surface in order to balance, climb and walk along branches effectively. The back legs are most specialised for climbing; they rotate hips and ankles so the soles of the rear feet can face the tail. This means the binturong is able to climb down trees head first with ease. The front paws, as well as aiding climbing, are also adapted to dig, and hold and open fruits, and the pads on the front feet are very soft. Each foot has five digits, with the front feet having one smaller digit, which it is able to use as an opposing thumb when it is grasping objects. The back toes split three to two, so no one digit is taking too much weight when climbing. The body shape of the binturong, being long, low and stocky, provides the animal with a low centre of gravity and even distribution of weight, which provides perfect balance for its arboreal behaviour. Though the binturong is well adapted to travelling among the tree tops, it is even able to walk upside down along branches with the aid of its tail, its movements are usually slow and deliberate.
During the daytime the binturong spends the majority of their time lying in the tree tops. They are nocturnal in the large part, so will pass the day sleeping. Through the night, the binturong will forage for food and spend time travelling around their area of the forest. During Rozhnov’s observations of a wild caught male binturong, he noted that the animal’s locomotor activity in October to November began about half an hour after dusk and the animal remained under cover during the day. The binturong’s pace when moving was around 1.5 metres per second, movements being gentle with the tail constantly employed to aid with balance. Binturong also display comfort behaviour; they will groom their own fur and that of other binturong in their family group. Grassman et al (2005) found five binturong tracked during a time period of 4-23 months had a mean annual range size of 6.2km², with a mean overlap of these ranges of 35%. These observed binturong appeared to be most active at twilight though a daily pattern of behaviour was not greatly distinctive.
The main tools the binturong uses to detect a possible food source at night are its whiskers. The whiskers are thick and sensitive, though not quite long enough to allow the binturong to determine whether a small space is passable or not. Binturong are primarily frugivorous, though they are classed as omnivores. They will also eat leaves, plant sprouts, small birds, eggs, lizards, small mammals, fish and carrion. They have a definite dietary preference for the fruit of the strangler fig, genus ficus, which are the primary canopy plants of their habitat. The wild caught binturong studied by Rozhnov was found to have only the fruits of ficus within its stomach. Binturong play an important role as seed dispersers of this genus of fruit. The outer coating of the seeds is broken down during the binturong’s digestive process in the intestines of the animal by a process called endozoochory. Therefore, when the seeds are passed they are in a form able to germinate. Binturong also play an important role in helping to control rodent populations within the forests they inhabit.
When in the wild, binturong tend to be solitary animals though small family groups are also seen, comprised of a male, female and one or two cubs almost all information known of a binturong’s reproductive behaviour has been gleamed from observations of captive animals, and therefore assumptions are made that this would be similar in wild animals. Within a study of captive binturong, Wemmer and Murtaugh (1981) note that females first copulated at mean age 30.4 months and first conceived at mean 30 months. Males achieved sexual maturity at a slightly younger age than females at mean 27.7 months.
Binturong live to between 10-15 years of age in captivity, their lifespan thought to be slightly less than this in the wild, and females have been observed to be fertile up to 15 years of age. Within captivity, binturong breed year round with a slight peak observed from January to March. Binturong are one of approximately 100 species of mammal capable of embryonic diapauses; the female is able to delay implantation of a fertile embryo in order to time birth to coincide with favourable environmental conditions. On occasion, female binturong show a moderate increase in aggression levels when they come into season. Males and females will mate several times while a female is in season, and this can last for as long as fourteen days. The oestrus cycle of the female had an average duration of 81.8 days (ibid).
The gestation period is around 90 days and females will give birth to 1-2 young. Litters as large as six have been seen in captivity, though survival of a whole litter of this size is not viable. Both parents will take an active role in the upbringing of the cubs until they reach independence at about one year of age. The females will give birth to their young in a protected area, usually some form of den or a tree hollow, providing shelter from the elements and cover from predators. Newborns are helpless, with eyes and ears closed, and emit a loud mewing noise when distressed. Both hands and tail display an innate grasping reflex present from birth. The binturong has focused vision by two to three weeks of age, and has developed sufficient balance for running, climbing and hanging by five weeks of age. The binturong also develops a wide repertoire of vocalisations while growing up, which it utilises when mature, including howling to announce its presence to any other binturong in the area. At six to eight weeks old, the binturong is an accomplished climber and through this achieves some independence from its parents at this age. The cubs will continue to suckle milk from their mother until around 16 weeks of age.
The binturong’s eyesight is not very well developed, and as well as the whiskers the animal also relies heavily on their sense of smell in order to evaluate their environment. Binturong actively scent mark their area and have a large perineal gland; in the male this is situated between the scrotum and the penis and in the female the gland is slightly smaller and anterior to the vulva. The positioning of the perineal gland means it comes into contact with any surface the binturong walks along, therefore they are able to scent mark with minimal effort. The smell of the binturong is very distinctive, though not unpleasant, and has been described to be similar to warm popcorn or corn bread. The binturong is capable of producing other scents; some mothers will mark their offspring with a scent similar to that of strong urine. Binturong can also emit a very pungent odour when extremely frightened; this is distributed as a fine spray of liquid which has an acrid smell and does give a burning sensation if inhaled. This behaviour is more common of the young binturong cubs, though adults are capable of spraying this scent too. It is also thought that the binturong uses its tail to communicate with other binturong in the area; the male will trail his tail through his urine, then brush his tail against trees and leave his scent anywhere he then travels.
Though IUCN presently classes the conservation status of the binturong as ‘least concern’, it is thought that their wild population is in decline. This is in part due to the loss of their habitat, as is the threat to so many animals indigenous to our rainforests. People local to the forests of South East Asia have always hunted mammals found there for food provisions; however there is now an ever-increasing profit to be made from catching and selling these animals to those who operate in the business of Chinese medicine. The penis bones of the binturong are of particular demand; they are ingested as a powder or added to food and thought to help a man stay virile and aid with the production of male children. Binturong are also desired as pets; as of 1998 a young individual of breeding age had a value of $1500 – $2500 in the exotic pet trade in the USA.