SILKY SIFAKA

Propithecus candidus

Geographic Distribution and Habitat
Silky sifakas, also known as silky simponas, inhabit montane and mid-altitude rainforests. They reside in a restricted range in northeastern Madagascar, mostly in Marojejy National Park and Anjanaharibe-Sub Special Reserve (ASSR). Although populations are more fragmented, they are also found in the Makira Natural Park and the corridor connecting Marojejy and ASSR known as COMATSA-Sud. They prefer to live at high elevations, greater than 2,300 ft (700 m) however, they can be found at elevations from 984 to 6,152 ft (300–1875 m).

TAXONOMIC NOTE

The silky sifaka was once considered to be a subspecies of the diademed sifaka (Propithecus diadema). Since 2007, the silky sifaka has been considered a unique species based on distinct morphological and molecular data when compared to the diademed sifaka.

Silky sifaka range, IUCN 2020

Size, Weight, and Lifespan
Species of sifaka in the genus Propithecus are often grouped according to size and geographic distribution. Larger bodied species like the silky sifaka live in the eastern and northeasters rainforests of Madagascar. Their body length ranges from 17.7 to 21 inches (45–53.5 cm). They weigh between 6.7 and 14.3 lbs (3.04–6.5 kg).

The lifespan of silky sifakas in the wild is unknown and they do not survive long in captivity. Another sifaka species, the Milne-Edwards’s sifaka (Propithecus edwardsi), can live up to 27 years; silky sifakas likely have a similar lifespan.

Appearance
Half of the silky sifakas’ name refers to their long, silky, creamy white pelage. (The other half, “sifaka,” refers to their distinct alarm calls. See Fun Facts on this page.) Their fur coloring ranges from white to silver-gray on their crown, back, and limbs with darker color tones on their lower back and the base of their tail. Sometimes the area at the base of their tail can be yellow.

For the most part, silky sifakas’ orange eyes are set in a bare gray or black face, although some of the silky sifakas found in Marojejy have virtually no facial skin pigment. These unique sifakas have pink or slate-gray faces. All silky sifakas have prominent black ears that peek out from the hair on their heads. 

Male and female lemurs are generally equivalent in body size. This holds true for silky sifakas as well. There is one immediately obvious and unique distinction between the sexes, however. The chests of adult male silky sifakas are stained brown from rubbing their sternal gular gland against tree trunks while scent-marking. The resulting “chest patch” increases in size throughout the mating season. Some chest patches become so large, they cover the entire chest and extend to the abdomen by the end of mating season. 

What Does It Mean?

Anthropogenic:
Environmental disturbance or environmental pollution originating in human activity. 

Allonursing:
Nursing by a female other than the biological mother.

Montane forest:
A forest that grows on the slope of a mountain, regardless of altitude or latitude, within a specific climate, just below the subalpine zone.

Polygynous:
A mating system in which one male mates and lives with multiple females.

Sexually dimorphic:
When males and females have different characteristics (size, color, etc.) other than their reproductive organs.

Visit the Glossary for more definitions

Silky Sifaka adult female carrying her own infant and the infant of another mother

Diet
Silky sifakas are folivorous seed predators, like other eastern sifakas. Most of their diet is comprised of young leaves (48.2%), fruits and seeds (41.8%), as well as flowers and buds (9.8%), and occasionally soil. Although they rely primarily on foliage, particularly in the dry season, they have a surprisingly diverse diet. They feed on more 100 trees, vines, and epiphytes.  Most preferred food tree genera include SymphoniaWeinmanniaLandolphia vines, Albizia, and Plagioscyphus trees.

All sifakas have gastrointestinal and dental specializations for folivory (leaf-eating) such as an enlarged cecum, a long gastrointestinal track, long gut passage time, and shearing crests on their molars.

Behavior and Lifestyle
Generally, all sifakas share a similar body shape, with long tails and legs relative to their torso and arms. Their long strong legs allow them to cling to vertical supports, such as tree trunks, and leap up to 30 ft (9 m) while traveling among the trees. At rest, sifakas cling to a support vertically while tucking their knees tightly to their abdomen and chest. While feeding or playing, they hang with their body suspended below or among tree branches. This is referred to as “suspensory behavior.”

The majority of their time is spent resting and foraging for food. The remaining time is spent socializing, grooming, and playing.  Grooming mostly takes place between the sexes and is initiated by males. Males have been observed engaging in more social behavior than females. Generally agonistic encounters are rare; however, when they occur they are between male-female dyads (or pair) over food resources. A dyad consists of two individuals that maintain a significant relationship such as a brother and sister, or mother and father. Females may behave aggressively towards males during feeding (female feeding priority).

Fun Facts

When leaping through the trees, the silky sifaka has a somewhat mysterious appearance from afar, due to their white fur, and is often called the “ghost of the forests” by locals.

The family name sifaka is due to the characteristic “shee-fak” alarm call.

Daily Life and Group Dynamics 
Group size ranges from two to nine individuals. Smaller groups of only three individuals usually consist of a male-female pair and their offspring. Larger groups usually consist of a single breeding adult male, up to two adult females, juveniles, and infants. Silky sifakas are territorial and home ranges vary by site from 41 to 61 hectares (101-151 acres).

While silky sifakas have not been studied as extensively as other members of the genus Propithecus, immigration and emigration of adult males has been confirmed. Female dispersal has been indirectly observed by the sudden disappearance of a subadult female, not due to predation, who was becoming more peripheral to the main group.

In Milne-Edwards’s sifakas (P. edwardsi)individuals of both sexes migrate from their natal group, with females leaving before maturity and males leaving both before and after maturity. Future research may reveal similar patterns of social behavior in the silky sifaka.

The flexibility in social organization and the mating system may be related to environmental factors such as increased feeding competition for seasonal resources and the presence of predators. Sifakas may balance the need for predator protection with limited feeding competition by keeping group size small and shifting the organization of the group throughout the year to enhance mating opportunities.

Communication
Like most sifakas, the silky sifaka has many forms of communication. Of them all, auditory communication is the most studied form. Adult eastern sifakas have about seven call types; infants have several specialized vocalizations as well. The most frequently emitted calls are low-amplitude, low-frequency, tonal “hum” and “mum” vocalizations. These calls are used in a variety of circumstances such as group movements, foraging, affiliation, or while resting. The loudest vocalizations produced are their alarm calls, which are often emitted by all group members. One of the most distinct alarm call is their sneeze-like “zzuss!” vocalization, which is produced with closed mouths in response to calls or howls by other group members, terrestrial disturbances, predators, or other high arousal situations. Studies have revealed sex and individual differences in “zzuss” vocalizations in silky sifakas.

The fossa (Cryptoprocta ferox) is the only documented predator of the silky sifaka, other than human beings. No aerial predation attempts by raptors have ever been observed, although these sifakas sometimes stare skyward and emit “aerial disturbance” roars in the presence of the Madagascar buzzard (Buteo brachypterus).

Olfactory communication is well-developed in sifakas. Eastern sifakas have several scent-marking glands that include a sebaceous chest gland only found in males, and mixed apocrine-sebaceous genital glands in both sexes. Sifakas, in contrast to Eulemur, do not allomark by directly scent marking conspecifics. Females scent-mark trees by rubbing their genital glands against them in a rhythmic vertical motion. Males, for their part, scent-mark trees in several different ways, by rubbing them with their chest gland, with their genital glands, or with a combination of the two. Males routinely gouge trees or bark bite with their toothcombs just prior to chest-marking, which leaves long-lasting visible marks and may promote scent longevity. Adult males frequently overmark female scent marks as well as other male marks, particularly as mating season approaches, by placing their scent mark directly on top.

Interestingly, female scent-marking rates are not highest during mating season—they peak just before lactation and dispersal season (individuals moving into a new home range or into new social groups). Male rates also peak during dispersal season. Since this is seen in Milne-Edwards’s sifakas (P. edwardsi) as well as other eastern sifakas, it is likely that the silky sifaka participates in similar scent-marking behaviors.

Reproduction and Family
Silky sifakas exhibit variable social structure with smaller groups mating monogamously and larger groups promiscuously with a polygynandrous mating system. However, the single dominant males in each group have been found to father the overwhelming majority of offspring in some sifaka species.

Females are in estrus on only one day the whole year in late December or early January with infants born in June or July. Generally, females give birth to a single infant every two years; only occasionally in consecutive years. Infants initially grasp the fur on their mother’s belly and, about four weeks later, begin to ride jockey-style on their mother’s back.

Most of the information on infant development and parental care in the eastern sifakas comes from what is known about Milne-Edwards’s sifakas. Within a group, births are synchronous (they occur at the same time). Usually this happens within a one-week window, with 6 to 8 births occurring in the group. The mother is the main caregiver, and infants spend more time with their mother than other group members. Non-mothers are also known to engage in infant care and participate in allonursing and carrying. Among sifakas, allonursing has been observed in the silky sifaka and the Milne-Edwards’s sifaka. Less extreme forms of allocare are seen in other sifaka species. 

Ecological Role
As a folivorous species that consumes both seeds and fruits, the silky sifaka is not known to be a seed disperser, although they may pass tiny ficus seeds.  Sifakas are prey for fossa, and defecate at high rates which is utilized by dung beetles and other species.

Conservation Status and Threats
Silky sifakas are one of the rarest and most threatened sifakas. They are listed as Critically Endangered by the International Union of the Conservation of Nature (IUCN, 2019). It is believed that there are fewer than 250 mature individuals, most of whom remain in Marojejy National Park and Anjanaharibe-Sub Special Reserve (ASSR). Although populations are more fragmented, this species is also found in the Makira Natural Park and the corridor connecting Marojejy and ASSR known as COMATSA-Sud.

Habitat destruction by slash-and-burn agriculture and hunting are the primary threats to the silky sifaka. In addition, illegal logging of rosewood and ebony threaten this species—as well as a recent resurgence in illegal mining in Anjanaharibe-Sub Special Reserve. There is no taboo against eating this species, so they are hunted for food. Anthropogenic impacts such as those listed cause extreme fluctuations in the population size of the silky sifaka as well as severely fragmented populations. The current population trend, however, is decreasing due to stress both on the ecosystem and the species.

Conservation Efforts
The silky sifaka is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES). They are found primarily in Marojejy National Park and ASSR. Some groups are found in the Anjanaharibe and Manandriana portions of Makira Natural Park and the COMATSA-Sud corridor. A small number of unexplored forest reserves and classified forests in northeastern Madagascar are assumed to be in their range. These forests have yet to be surveyed. Although they reside in “protected” areas or reserves, they still suffer from drastic habitat loss and hunting.

More efforts are needed to end lemur hunting in the Marojejy region and elsewhere. The Lemur Conservation Foundation (LCF) is currently supporting research and community development projects in Marojejy National Park and ASSR. LCF’s conservation program, which is based on the IUCN’s Lemur Action Plan, emphasize ecotourism, environmental education, forest monitoring, and population-health-environment (PHE). In recent years, Camp Mantella and Camp Marojejia in Marojejy were completely rebuilt and Camp Indri was created in ASSR as the first and only camp for researchers, tourists, and students.

LCF’s conservation programs, which are based on the IUCN Lemur Action Plan, emphasize ecotourism, environmental education, research, park and lemur protection, reforestation, sustainable livelihood, and Population/Health/Environment (PHE) programs. Ecotourism projects have included rebuilding the dining area and bungalows at Marojejy’s Camp Mantella as well as the construction of tent shelters, a dining area, shower, and toilet for Camp Indri, the sole camping site for Anjanaharibe-Sud Special Reserve. The camps not only bring tourists and researchers but give local school groups a chance to view exceptional wildlife in primary forests during overnight fieldtrips led by LCF.

To help preserve the biodiversity of these mountainous rainforest habitats, LCF works in collaboration with Madagascar National Parks to conduct forest monitoring, lemur surveys, and park boundary demarcation. LCF also supports hospital nurses from Marie Stopes who provide family planning counseling and services in remote areas without access to healthcare. To fight deforestation in the SAVA region, LCF manages a reforestation program directly with local reserves and Graine de Vie and provides fuel-efficient cook stoves produced by the Swiss-Malagasy nonprofit ADES. 

OUR THANKS

Our gratitude to Dr. Erik R. Patel, Conservation and Research Director, at the Lemur Conservation Foundation for generously amending this profile in September 2021 with the most current data about this Critically Endangered lemur species. 

The Lemur Conservation Foundation is dedicated to the preservation and conservation of the primates of Madagascar through managed breeding, scientific research, education, and art.

References:

  • http://pin.primate.wisc.edu/factsheets/entry/diademed_sifaka/behav
  • https://metode.org/issues/monographs/dispersal-in-primates/
  • https://animaldiversity.org/accounts/Propithecus_candidus/
  • https://animals.sandiegozoo.org/animals/coquerels-sifaka
  • https://www.iucnredlist.org/species/18360/8142320
  • Patel, ER., Marshall, JJ., & Parathian, H. 2005. Silky Sifaka (Propithecus candidus) Conservation Education in Northeastern Madagascar. 44 (3): 8-11.
  • Patel, ER., Owen, MJ. 2012. Silky sifaka (Propithecus candidus) “zzuss” vocalizations: Sexual dimorphism, individuality, and function in the alarm call of a monomorphic lemur. Journal of Acoustical Society of America. 132 (3): 1799-1810. 
  • Mittermeier, R., Konstant,W., Hawkins, F., Louis,E., Langrand, O.,  Ratsimbazafy, J., Rasoloarison, R., Ganzhorn, J., Rajaobelina, S., Tatersall, I., Meyers, D. 2006. Lemurs of Madagascar. Washington, D.C.: Conservation International.
  • Irwin, M. 2007. Ecologically Enigmatic Lemurs: The Sifakas of the Eastern Forests (Propithecus candidus, P. diadema, P. edwardsi, P. perrieri, and P. tattersalli). 305-326.

Written by Tara Covert, October 2019. Revised September 2021.