Propithecus candidus, Grandidier, 1871

Russell A. Mittermeier, Anthony B. Rylands & Don E. Wilson, 2013, Indriidae, Handbook of the Mammals of the World – Volume 3 Primates, Barcelona: Lynx Edicions, pp. 142-175 : 172-173

17.

Silky Sifaka

Propithecus candidus

French: Sifaka soyeux / German: Seidensifaka / Spanish: Sifaca sedoso

Other common names: Silky Simpona

Taxonomy. Propithecus candidus Grandidier, 1871 ,

Madagascar, north of Bay of Antongil.

Variations in this taxon approach P. diadema. P. candidus may be the only member of its genus to show extreme individual variation in partial skin pigmentation loss, known as leucism. Although all infants are believed to be born with predominantly black faces, with age some individuals lose their pigmentation and show varying degrees of pink patches. The first western explorer to observe P. candidus was A. Grandidier in 1871, and he believed that it was an albino subspecies of P. diadema . All individuals have some skin pigment, and photo-phobic individuals have never been observed. Monotypic.

Distribution. Restricted and patchy range in NE Madagascar that includes the humid forest belt extending from the Marojejy Massif and the Andapa Basin to Maroantsetra; the Androranga River may be the NE distributional limit in the Tsaratanana Corridor, although further surveys are needed to confirm this, and the Antainambalana River in the Makira Forest protected area is currently regarded as the S boundary. Currently, Marojejy represents the N limit ofits distribution, although historic range maps suggest that it once occurred as far N as the Bemarivo River near Sambava. The NE distributional limit in Makira was only recently established, when a few groups were found in the Antohaka Lava Forest, but informal reports suggest that the unprotected Maherivaratra Forest, outside NE Makira, may also contain Silky Sifakas.

Descriptive notes. Head-body 48-54 cm,tail 45-51 cm; weight 5-6 kg. The Silky Sifaka is a large white sifaka, with notably long and silky fur, which gives this species its common English name. Males and females are similar in size. Females are mainly creamywhite, with some individuals having silvery-gray tints on the crown, back, and limbs. There is usually a patch of rust-red (sometimes yellow) fur on the base of the tail. The muzzle and face are bare and normally slaty-gray-black (often with pinkish mottling around the mouth), but some individuals have all pink or all black faces. Tips of the naked black or pink ears protrude just beyond the white fur of the head and cheeks. Eyes are a deep orange-red. Adult males are readily distinguished from females by the pelage color on the upper chest; they have a large brown patch on the upper chest that results from scent marking with the sternal-gular gland. As rates of scent marking by males increase during the mating season, these chest patches become larger in size and can cover the entire front torso to the abdomen. Some Silky Sifakas in the Marojejy Massif have entirely pinkish faces and dark fur across their upper back and shoulders.

Habitat. Several types of elevation-specific habitats and, despite its extreme rarity, the greatest elevational range of any sifaka. In Marojejy and in Anjanaharibe-Sud, Silky Sifakas are most often encountered in undisturbed humid primary and montane rainforest at elevations of 700-1900 m. They are sometimes found in sclerophyllous forest and even low ericoid bush near their highest elevations. The southernmost Silky Sifakas in Makira adjacent to the Antainambalana River inhabit an unusually low-elevation forest fragment at 300-600 m.

Food and Feeding. The Silky Sifaka is a folivore and seed predator that consumes a wide variety of plant species. A three-month dietary study at Marojejy National Park documented use of 76 species in 42 families (mainly trees but also many lianas and epiphytes). The most important plant families in the diet were Moraceae , Fabaceae , Myrtaceae , Clusiaceae , and Apocynaceae . Fruit from Pachytrophe dimepate ( Moraceae ), seeds from Senna (Fabaceae) , young leaves from Plectaneia thouarsii ( Apocynaceae ), and fruit from Eugenia (Myrtaceae) were the most preferred and accounted for ¢.37% of total feeding time. Overall, 52% of feeding time of Silky Sifakas was spent eating young and mature leaves, 34% ripe fruit, and 11% seeds. Flowers, bark, and soil were rarely eaten.

Breeding. Mating is believed to occur on a single day each year in December—January. Generally, female Silky Sifakas give birth to a single infant every two years and only occasionally in consecutive years. Births take place in June-July, after gestation of ¢.179 days. Infants initially grasp the fur of their mother’s belly and transfer to her back at about four weeks, riding jockey-style. Until they approach maturity, offspring always sleep with their mothers. As is typical of Propithecus , all group members interact with infants. Grooming is the most frequent form of alloparental care, followed by playing and occasional carrying; nursing has been observed in a few remarkable instances. Mothers have been seen simultaneously nursing both newborn and older offspring. Interbirth interval averages 1-7 years, but it is affected by whether or not an infant survives its first year.

Activity patterns. The Silky Sifaka is diurnal and arboreal. Adults spend most of their day resting (44-4%) and foraging (21-9%), but they also devote a substantial amount of time to social behavior (16:8%). Long bouts of terrestrial play involving adults are not uncommon.

Movements, Home range and Social organization. The Silky Sifaka has been discussed in several survey reports and was the subject of two short-term studies. As with other eastern sifakas, it has a variable social structure, living in both pair-bonded and multimale-multifemale groups of up to nine individuals. Smaller groups of 3—4 individuals probably consist of an adult pair plus their offspring, while larger groups likely consist of mutually familiar foraging units that may contain more than one breeding pair and juveniles. Home range size varies by site, ranging 34-47 ha. Daily movement averages 712 m. Exclusive territories are maintained, although there is little aggression over boundaries. Males emigrate at age five to a neighboring group. Although male and female dispersal is typical in eastern sifakas, female dispersal has not been observed. Rates of aggression are low and mainly occur during feeding. Females have feeding priority over males. Two populations from Marojejy National Park had densities of 40 ind/km? and 90 ind/km?, each estimate from a different elevational range. Generally, Silky Sifakas occur at very low densities.

Status and Conservation. CITES Appendix I. Classified as Critically Endangered on The IUCN Red List. The Silky Sifaka is one of the rarest and most endangered sifakas, and it has been on the list of the World’s 25 Most Endangered Primates , produced jointly by the IUCN/SSC Primate Specialist Group, the International Primatological Society, and Conservation International, since its inception in 2000. Main threats are habitat destruction and hunting, which occur even within supposedly protected areas. There is no local “fady” (taboo) against eating Silky Sifakas, as exists for the Indri in at least some parts ofits distribution. The situation has become even more severe since the political upheavals of early 2009. The Silky Sifaka is known to occur in the Anjanaharibe-Sud Special Reserve and Marojejy National Park. Unfortunately, Marojejy was one of the first protected areas to be hit by a wave ofillegal rosewood logging shortly after the coup that ousted President M. Ravalomanana.It is very possible that hunting of Silky Sifakas accompanied these incursions, but this remains to be confirmed. Populations also are found in the forests of Makira (currently under temporary government protection), the Betaolana Corridor, and possibly some unsurveyed forest fragments south-east of Marojejy (e.g. Andranomenabe and Maherivaratra). Efforts should be made to stop the hunting of sifaka in Marojejy and elsewhere. The total world population is believed to number only a few hundred individuals, down from somewhatless than 1000 in 1992.

Bibliography. Cousins (2007), Duckworth et al. (1995), Groves (2001), Kelley & Mayor (2002), Lehman et al. (2005), Mittermeier et al. (2010), Patel (2005, 2006a, 2006b, 2007a, 2007b, 2009a, 2009b, 2010), Patel & Andrianandrasana (2008), Patel et al. (2005), Pochron et al. (2004), Rasolofoson, Rakotondratsimba, Rakotoirainy, Rakotozafy et al. (2007), Rasolofoson, Rakotondratsimba, Rakotoirainy, Rasolofoharivelo et al. (2007), Sterling & McFadden (2000), Tattersall (1982, 1986b), Wilmé & Callmander (2006).

Figures

On following pages: 12. Crowned Sifaka (Propithecus coronatus); 13. Coquerel’s Sifaka (Propithecus coquerell); 14. Tattersall’s Sifaka (Propithecus tattersall); 15. Diademed Sifaka (Propithecus diadema); 16. Milne-Edwards's Sifaka (Propithecus edwardsi); 17. Silky Sifaka (Propithecus candidus); 18. Perrier’s Sifaka (Propithecus perrieri).

Distribution. Restricted and patchy range in NE Madagascar that includes the humid forest belt extending from the Marojejy Massif and the Andapa Basin to Maroantsetra; the Androranga River may be the NE distributional limit in the Tsaratanana Corridor, although further surveys are needed to confirm this, and the Antainambalana River in the Makira Forest protected area is currently regarded as the S boundary. Currently, Marojejy represents the N limit ofits distribution, although historic range maps suggest that it once occurred as far N as the Bemarivo River near Sambava. The NE distributional limit in Makira was only recently established, when a few groups were found in the Antohaka Lava Forest, but informal reports suggest that the unprotected Maherivaratra Forest, outside NE Makira, may also contain Silky Sifakas.