The silky sifaka (Propithecus candidus), also known as silky simpona, is a large lemur that is native only to the island of Madagascar. This lemur is one of the rarest creatures on earth, because it is so endangered and because of its small range. It is one of only nine sifaka species of lemur, and was previously thought to have been a subspecies of the diademed sifaka until 2007.
Its range is extremely limited to the northeastern strip of a damp forest extending from the southern Maroantsetra north to the Andapa Basin and the Marojejy Massif. Marojejy National Park represents the northern most extent of its range. Maps created in the nineteenth century by Grandidier and Milne-Edwards show that the northern range of the silky sifaka extended as far as the Bemarivo River, which is north of Sambava. It is thought that the Androranga River may represent the northwestern limit of its range within the Tsaratanana Corridor. In 2009, observations were noted of a few small groups of silky sifakas residing in fragmented areas neighboring northeastern Makira, in Antohaka Lava and Maherivaratra. This could possibly extend their range a bit further. It is thought that the boundary for its southern range is the Antainambalana River, in the Makira Conservation Site, but it is not known if its southern range has stretched as far south as the Masoala Peninsula.
The silky sifaka prefers to live at high elevations of up to 6,152 feet within Marojejy National Park and Anjanaharibe-Sud Special Reserve where most of its populations reside. It does live below 2,300 feet, except in Makira where it resides at a level of 980 feet. Within their habitats, they reside in sclerophyllous forest areas, montane rainforest areas, and higher portions of low ericoid bush. It is not known if they avoid habitat edges, but they do not cross fragmented forest areas, as is typical to most lemurs.
The silky sifaka derives its common name from vocalizations that it commonly makes. Sifaka represent the call it emits when alarmed, a harsh, hiss-like “shee-faak. The larger diademed sifaka is known as a simpona on the eastern coasts within its range, and this name sounds similar to the “sneeze” alarm that the lemurs emit as a “zzuss” sound. The scientific species name of candidus means “white” in Latin, while the taxonomic synonym sericeus means, “silk” the Greek language.
In 1871, French naturalist Alfred Grandidier first described the silky sifaka, presenting his work in a published letter to French zoologist Alphonse Milne-Edwards. After observing the lemur in late 1870, north of the Bay of Antongil, he named it Propithecus candidus because of its soft white fur, and he compared it to Verreaux’s sifaka, noting the distinct color differences. A planter in Sambava, named “Monsieur Guinet”, acquired the first individual studied in 1872. This individual allowed Grandidier and Milne-Edwards to better understand the silky sifaka and describe it in more detail. After their observations were complete, they renamed the lemur P. sericeus, although the former name of Propithecus candidus took priority in 1931 when Ernst Schwarz organized lemur taxonomy and classified it as a subspecies.
Schwarz classified sifakas into only two species categories, with four subspecies in each. The larger diademed sifaka, from the eastern rainforests, held that the silky sifaka was a subspecies, due to the variations in color representing only differences between the same species. This thought was upheld through 2001, when Colin Groves reviewed the taxonomic placements of the lemurs, stating that he found them to be accurate. He later suggested that that the color differences did not overlay as once was thought, and that they signified two separate species of sifaka.
The theory that the silky sifaka was a separate species from the larger diademed sifaka was solved in 2004, when Mayor et al revealed that the silky sifaka was genetically distinct from the larger diademed sifaka. The short and nearly lack of a tail, along with other characteristics, supported the silky sifaka’s separate classification, although Groves did not recognize this until 2007 after making observations of his own about its long molar teeth.
The silky sifaka is still recognized within the group of diademed sifakas, along with the diademed sifaka, Milne-Edwards’ sifaka, and Perrier’s sifaka. All experts in the subject have not yet supported the sifaka distinctions, however. Tattersall noted in 2007 that the distinct classifications of Propithecus were made preemptively. Despite this, he sighted what he supposed to be a colored variation of the silky sifaka in in northeast Madagascar, north of Vohemar. He described it in The Primates of Madagascar eight years later, observing the typical creamy fur as well as the unusual tufted ears and spot of orange fur on the crown. In 1986, it was spotted again by the paleoanthropologist Elwyn Simons and his team, who captured specimens for breeding and in 1988, it was classified as the distinct species of golden-crowned sifaka (Propithecus tattersalli).
The silky sifaka ranges in body and tail length equaling 3.1 to 3.4 feet, making it one of the largest of the sifakas. It has an average weight that can be up to fourteen pounds. The long fur is creamy white and silky in quality, as the name suggests. Some color variations do occur, but they are limited to silvery gray or dark patches of fur on the limbs, crown, and back and the base of tail can sometimes be yellowish in color. The distinct, hairless face can sometimes be a mixture of black and pink, all pink, or all black. The eyes are typically reddish orange, and its distinct features provide no room for confusion among other sifakas, as well as its limited range.
Unlike other species of sifakas, it is possible to distinguish between males and females by looking at the chest coloration. Males display a dark reddish brown patch due to the sternal gular gland, a scent gland that grows to encompass the chest and abdomen during mating season. Female silky sifakas have a chest that remains white.
The silky sifaka lives in a variable social structure, with groups that range from two through nine individuals. Groups can contain a male and female pair, one male and many females, or a varied number of males and females. The average home range of a group of silky sifakas is thought to be around 0.13 to 0.18 square miles. Typically, there are no dominance hierarchies within groups, although during mating season they may occur. Aggression is also limited, except during feeding time where females take precedence and there are not always submissive signals.
Recent studied have found that the silky sifaka will spend approximately 44.4 percent of its time resting and 16 percent of its time eating. 16.8 percent of this lemur’s day is dedicated to social behaviors like grooming, social rooming, and playtime. Any amount of time that is left over is spent foraging for food or traveling. Other studies have suggested that the silky sifaka will split its day in half, spending a fourth of its time foraging, and another fourth traveling. This study found that it spent the rest of its day resting. When traveling, the group is typically led by the females, and it can travel up to 2,300 feet in a day. The silky sifaka, like other lemurs, moves vertically through trees through a process known as “clinging and leaping”, and it can travel a height of up to 1,600 feet in one day. Playtime is important to these lemurs, and they will spend thirty minutes or more cavorting in the trees and even on the ground.
The silky sifaka typically begins to forage around dawn, unless it has rained recently. It prefers a diverse diet of leaves and seeds, among other plant materials. A recent two-month study found that this lemur will eat up to seventy-six different species of plant, with a preference for tree plant materials. Approximately thirty seven percent of its feeding time may be spent eating from the plant families of Moraceae, Fabaceae, Myrtaceae, Clusiaceae, and Apocynaceae, in order of preference. Around sixteen percent of feeding time may be spent on eating fruit.
Like other eastern sifakas, the silky sifaka has a slightly large range of calls, at up to seven different kinds. Although the circumstance of the calls is not yet known, it is thought that arousal level may play a role in the frequency and level at which a silky sifaka calls. The main calls, a “hum” or “mum” vocalization, it used when foraging, resting, traveling, and during social activities. Even young sifiakas are known to have several distinct vocalizations.
The silky sifaka will also use different vocalizations when danger is sighted. Although it does not have many predators, it uses two different calls for ground and aerial threats. The main aerial threat, the Madagascar buzzard, will cause the lemur to emit a roar vocalization, alerting others to the presence of the bird. Terrestrial threats include the fossa, a cat like creature native to Madagascar. This threat causes a more general alarm call, a “zzuss” vocalization that is also used in individual aggression among groups. This call’s structure varies in male and female silky sifakas.
Scent marking is another common form of communication between sifakas, and they have advanced olfactory glands that aid in this method. Males have a sebaceous gland on the chest, while both sexes have mixed apocrine-sebaceous glands the genitals. Unlike true lemurs from the genus Eulemur, silky sifakas do not mark members of the group with their scent, but will mark territories and urinating while scent marking is common between both sexes, although they differ in methods of marking. Males will use their chest or genitals to mark something, while the female will use only her genitals. Males have also been known to use their toothcomb to scrape visible markings on trees before rubbing their scent glands on them. This is strictly used for marking, as male silky sifakas do not eat the bark or trees.
Another difference in scent marking occurring between male and female silky sifakas is the frequency of the action. Males tend to scent mark three times more often than females, and will often override a female’s mark with its own. They have been known to mark over other male’s scents, although this does not occur as often. A study conducted over a one-year period showed that a male silky sifaka reacted to seventy-one percent of female markings within sixty-one seconds, while male markings only comprised seventeen percent. It was also found the “totem tree marking” is most commonly executed on the trees within the central area of a territory, rather than the trees along the border of that territory.
The silky sifaka breeding season occurs through the months of December and January, and it is thought that they possibly only breed on one day during those months. Young sifakas are born six months later between the months of June and July. Typically, births consist of only one baby every two years, although more frequent births have occurred. The baby sifaka will latch onto the belly of its mother for up to a month, after which it will move to the mother’s back. As is typical to eastern sifakas, babies mature quickly, and it is thought that is due to alloparenting, when many individuals will care for an infant. Most alloparenting involves grooming and playing, although carrying and nursing can occur. It is thought that lemurs of this species who have reached sexual maturity will leave their endemic group, although this was only observed with one male. Female dispersal has not yet been discovered.
The silky sifaka has been listed on the IUCN Red List as “Critically Endangered” and is one of the “The World’s 25 Most Endangered Primates”. It is estimated the amount of these lemurs in the wild only reaches a number of 1,000, with 250 being mature adults, and there are no individuals in captivity. However, in Marojejy ,which was recently inducted as a part of the World Heritage Site cluster known as the Rainforests of the Atsinanana, the silky sifaka is considered a flag-ship species.
Despite the efforts to save the silky sifaka, it is threatened by habitat destruction due to slash-and-burn agriculture and logging, and by excessive hunting. Unlike the golden-crowned sifiaka, there is no local taboo, or fady, that protects the lemur from being killed for bush meat. It is mainly hunted in parts of the Andapa Basin, as well as in the northern and western parts of Marojejy. Only 350 square miles of its range make up protected areas, and this is thought to be an overestimation due to the particular altitudes at which the silky sifaka resides.
Although hunting is a main threat to the silky sifaka, the main threat is illegal logging throughout its protected range. Trees such as ebony and rosewood are detrimental to the sifaka’s habitat, and this causes an increase of invasive species flourishing and species diversity decreasing. Forest fires are also more common because of selective logging.
Villages that surround the remainder of the silky sifaka’s protected habitat have implemented a two-part educational strategy to help preserve the low numbers of the lemur species. Slide presentations, radio interviews, and conservation literature are among the methods used to educate students in twelve primary and secondary schools in these regions. The second part if these efforts consisted of creating an “emotional link” between children and the silky sifaka, in order to cause awareness of the dwindling numbers and struggles of the sifaka. This was accomplished by taking groups children and teachers on three-day educational tours through the Marojejy National Park, after which both students and teachers showed genuine concern for the silky sifaka’s preservation.
Other efforts include the enlargement of Anjanaharibe-Sud Special Reserve and the linking between it and other protected areas with wildlife corridors including the Betaolana Corridor. This corridor would link Anjananharibe-Sud to Masoala National Park in the south, and currently connects to Marojejy. This joining would not only create more suitable habitat for the silky sifaka, but would also create genetic exchange between other isolated populations of the lemur.
Image Caption: Silky Sifaka Propithecus candidus, Marojejy National Park, Madagascar. Credit: Jeff Gibbs/Wikipedia(CC BY-SA 3.0)