Propithecus candidus

Geographic Range

Silky sifakas inhabit a limited range in northwestern Madagascar, extending from Maroantsetra to the Andapa Basin. Their range extends to the Antainambalana River in the south and Maraojejy National Park to the north, though they have been spotted as far north as the Bemarivo River near Sambava. Their range is bounded on the northwest by the Androranga River in the Tsaratanana Corridor. Several groups of silky sifakas have also been sighted in northeastern Makira, though these sightings have yet to be confirmed. The majority of silky sifakas are found in two protected areas in Madagascar: Maraojejy National Park and the Anjanaharibe-Sud Special Reserve. Silky sifakas are rare throughout their range and are not sympatric with any other species of sifakas.

• Biogeographic Regions
• ethiopian ethiopian
  • native native

• Other Geographic Terms
• island endemic island endemic

Habitat

Silky sifakas primarily inhabit montane and mid-altitude rainforest in Madagascar, which experiences a mean annual rainfall of about 2,500 cm. They have the most variable range in elevation of any of the sifakas, ranging from 300 m in Andaparaty to 1875 m in Marojejy. Despite this range, silky sifakas generally prefer elevations greater than 800 m. They thus inhabit a number of habitats found only at high elevations, including sclerophyllous forest and low ericoid bush at the highest part of their range.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• rainforest rainforest

Physical Description

Propithecus candida was once considered a subspecies of Propithecus diadema . It has recently been elevated to species status based on morphological and molecular data that suggest it is distinct from P. diadema .

Silky sifakas range in body length from 48-54 cm, in tail length from 45-51 cm, and in weight from 5 to 6.5 kg. Silky sifakas have a long, silky creamy white pelage. Some individuals possess silver-grey coloring on the crown, back, and limbs and darker coloring on the lower back and base of the tail. The region at the base of their tail can sometimes be yellow. Their face is bare and slate-grey black with deep orange eyes, though a few individuals found in Marojejy have no skin pigment in their face and have pink or slate-grey faces. Unlike P. diadema , their bare ears are black and prominent, protruding beyond the fur of the head.

Unlike other species of sifaka, silky sifakas are sexually dimorphic in that males have a chest patch that is brown in color and which increases in size throughout the mating season. Some chest patches can cover the entire chest and extend to the abdomen by the end of the mating season. Other than this chest patch, males and females are monomorphic in terms of size and coloring.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes colored or patterned differently

Reproduction

Not much is known about the mating system of silky sifakas. They are highly variable in their social structure, living in multi-male and/or multi-female groups, male-female groups, or single-male groups. Due to this variety in social structure, silky sifakas can be either polygynous or pair-bonded.

• Mating System
• monogamous monogamous
• polygynous polygynous
• cooperative breeder cooperative breeder

It is thought that mating happens on a few days in November, December, or January every year. Infants are born in June or July. Mothers give birth to single offspring every two years, though births on consecutive years have also been observed. The average interbirth interval for silky sifakas is 1.67 years, which is less than most rainforest sifakas.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• viviparous viviparous

Like all sifakas, silky sifakas display a high degree of maternal care. Infants cling to their mother’s belly after birth. When they reach 4 weeks old, they ride on their mother’s back. Infants sleep with their mothers until they reach maturity.

Non-maternal care has been well documented in silky sifakas; it is typical for all group members to interact with infants. Allocare is performed by adult individuals regardless of age and sex on infants ranging from the first few weeks to twenty four weeks old. Grooming is the most common form of allocare, followed by playing, carrying, and nursing. It has been observed that as an infant ages, the amount of non-maternal grooming decreases and amount of non-maternal playing increases. Propithecus candida and Propithecus edwardsi are the only members of the genus Propithecus where allonursing has been observed.

• Parental Investment
• altricial altricial
• female parental care female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
• extended period of juvenile learning

Lifespan/Longevity

The lifespan of this species in the wild is unknown, and silky sifakas do not survive in captivity. The closest estimate of lifespan thus comes from closely related species of sifaka. Propithecus verreauxi has been observed to live beyond 23 years of age. Silky sifakas likely have a similar life span.

Behavior

Silky sifakas spend the majority of their time resting and foraging. About 45% of each day is spent at rest, while 22% is spent searching for food. The rest of the day is spent on social behavior, such as grooming and playing. A very small part of the day is spent moving. It has been observed that males generally move around and engage in more social behavior than females, while females generally rest more than males.

Silky sifakas are vertical clingers and leapers like all other sifakas. When at rest, they are typically found clinging to vertical tree trunks, with knees flexed and held close to the abdomen. They move through the canopy by quickly extending their legs and jumping from one vertical support to the next. They also exhibit suspensory behavior especially when feeding or playing. Group size ranges from two to nine individuals. Groups of only three or four individuals usually consist of a male-female pair and their offspring, while larger groups probably consist of larger foraging units of more than one breeding pair with offspring and juveniles.

While agonistic encounters are generally rare, the majority of these encounters occur between male-female dyads over contested resources like food. Females generally have feeding priority over males. The outcome of agonistic encounters does not favor either sex. Allogrooming between sexes has been observed, though it is rarer than allogrooming among members of the same sex. In the vast majority of instances where allogrooming between sexes was observed, it was initiated by the male.

Not much is known about individual dispersal between groups of silky sifakas. Dispersal has only been observed once, when a young male entered a group and forced out an older dominant male that had been part of the group for more than seven years. Female-based dispersal, though never observed, probably also occurs similar to that of other species of sifaka.

• Key Behaviors
• arboreal arboreal
• scansorial
• saltatorial saltatorial
• diurnal diurnal
• motile motile
• social social

Home Range

Silky sifaka home ranges are between 34 and 47 ha in area.

Communication and Perception

Silky sifakas, like all lemurs, are varied in their modes of communication. Their most-studied form of communication is auditory. Adult vocalizations include seven distinct calls. Silky sifakas communicate by emitting a distinct zzuss sound. Individuals emit this sound in the following circumstances: when there is a terrestrial disturbance, such as a predator spotting, when responding to the howl of a distant group member, and spontaneously while resting. Under rarer circumstances, individuals emit the zzuss vocalization in response to an aerial disturbance, when other lemur species are present, or during agonistic interactions within a group. The majority of vocalizations occur in the morning, the time of day that the silky sifaka’s main predator, the fossa, is most active. Silky sifakas show sex and identity-related variation in their zzuss sounds.

Silky sifakas also use olfaction and scent-marking as a means of communication similar to other prosimians. All eastern sifakas possess specialized scent-marking glands. Males possess a characteristic sebaceous chest gland and both males and females possess apocrine-sebaceous genital glands. Males scent-mark trees by rubbing their genital gland and/or chest gland vertically against the bark. Males also gouge trees using their toothcombs before scent-marking, an act that is considered to be a form of communication because silky sifakas do not eat tree bark or gums. Both males and females urinate while scent-marking. Male silky sifakas spend more time than females scent-marking, though it has been observed that female scent-marks are more likely to get a response by group members. As with P. edwardsi the most common type of overmarking that occurs is when males overmark a female scent. Though rates of scent-marking are high, silky sifakas have never been observed scent-marking the boundaries of their home ranges.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• scent marks scent marks

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Silky sifakas are mainly folivores. Their diet mostly consists of mature and young leaves, seeds, fruits, and flowers. They also rarely eat flowers, bark, and soil. In one study, more than half (52%) of the silky sifaka’s feeding time was spent eating leaves, while about 34% and 11% of their feeding time was spent eating fruit and seeds, respectively. Silky sifakas feed on a wide range of plants. They have been observed to eat from 76 species, encompassing 42 families of plants. The most important plant families in the silky sifaka’s diet are Moraceae, Fabaceae, Myrtaceae, Clusiaceae, and Apocynaceae. The foods that they prefer to eat the most are Pachytrophe dimepate fruit, Senna seeds, Plectaneia thouarsii leaves, and Eugenia leaves.

• Primary Diet
• herbivore herbivore
  • folivore folivore
  • frugivore frugivore
  • granivore granivore
  • lignivore

• Plant Foods
• leaves
• wood, bark, or stems
• seeds, grains, and nuts
• fruit
• flowers

Predation

The two main predators of the silky sifakas are humans and the fossa Cryptoprocta ferox . Silky sifakas are hunted by humans for food and there is no local taboo against eating silky sifaka meat. The fossa is the largest extant carnivore on Madagascar and it is the most common predator of species of the genus Propithecus . Predation of Propithecus candidus by a fossa has been observed in nature.

Other than humans and the fossa, it is unclear whether silky sifakas are eaten by other predators. Silky sifakas often stare upward and sometimes emit aerial disturbance roars in response to the Madagascar buzzard Buteo brachypterus . This raptor does not feed on lemurs, however, and it is unknown if other birds of prey pose a risk to silky sifakas.

Ecosystem Roles

The role that silky sifakas play in their ecosystem is unknown. As a primarily folivorous organism that eats both seeds and fruits, it is likely that they play an important role in seed dispersal. Silky sifakas are also a food source for humans and fossas.

• Ecosystem Impact
• disperses seeds

Economic Importance for Humans: Positive

Silky sifakas are hunted for food. There are no other known positive effects of this species on humans other than the ecosystem role it provides in seed dispersal.

• Positive Impacts
• food food

Economic Importance for Humans: Negative

Silky sifakas have no known negative impacts on humans.

Conservation Status

The silky sifaka is listed as critically endangered on the IUCN Red List. It is also listed on Appendix I of CITES. Additionally, it was included on both the International Primatological Society and Conservation International lists of the world’s 25 most endangered primates in 2008.

Propithecus candidus is one of the most critically endangered lemurs in Madagascar. There are an estimated 250 adult individuals remaining today, a number that is most probably decreasing. The greatest threats to silky sifakas are habitat disturbance and hunting. There is no local taboo, or fady, against hunting and eating silky sifakas as there is for Indri indri . They even face the effects of habitat destruction and hunting in the two protected areas in which they are found, Marojejy National Park and the Anjanaharibe-Sud Special Reserve.

Additional Links

Encyclopedia of Life

Contributors

Maria Correa (author), Yale University, Eric Sargis (editor), Yale University.

References

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Garbutt, N. 1999. Mammals of Madagascar . New Haven, Connecticut: Yale University Press.

Kelley, E. 2002. Preliminary study of the silky sifaka ( Propithecus diadema candidus ) in northeast Madagascar. Lemur News , 7: 16-18.

Lehman, S., M. Mayor, P. Wright. 2005. Ecogeographic size variations in sifakas: a test of the resource seasonality resource quality hypotheses. American Journal of Physical Anthropology , 126: 318-328.

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Patel, E., M. Owren. 2012. Silky sifaka ( Propithecus candidus ) "zzuss" vocalizations: sexual dimorphism, individuality, and function in the alarm call of a monomorphic lemur. Journal of the Acoustical Society of America , 133: 1799-1810.

Patel, E. 2006. Activity budget, ranging, and group size in silky sifakas ( Propithecus candidus ). Lemur News , 11: 42-45.

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Patel, E. 2009. Silky Sifaka. Pp. 23-26 in Primates in Peril: The World's 25 Most Endangered Primate 2008-2010 . Arlington, VA: Conservation International.

Patel, E. 2005. Silky sifaka predation ( Propithecus candidus ) by a fossa ( Cryptoprocta ferox ). Lemur News , 10: 25-27.

Richard, A., R. Dewar, M. Schwartz, J. Ratsirarson. 2002. Life in the slow lane? Demography and life histories of male and female sifaka ( Propithecus verreauxi verreauxi ). Journal of the Zoological Society of London , 256: 421-436.

Tattersall, I. 1982. The Primates of Madagascar . New York: Columbia University Press.