|Distribution of P. verreauxi|
Verreaux's sifaka (Propithecus verreauxi), or the white sifaka, is a medium-sized primate in one of the lemur families, the Indriidae. It lives in Madagascar and can be found in a variety of habitats from rainforest to dry deciduous forests of western Madagascar and the spiny thickets of the south. Its fur is thick and silky and generally white with brown on the sides, top of the head, and on the arms. Like all sifakas, it has a long tail that it uses as a balance when leaping from tree to tree. However, its body is so highly adapted to an arboreal existence, on the ground its only means of locomotion is hopping. The species lives in small troops which forage for food.
In adulthood, the full head and body length is between 42.5 and 45 cm (16.7 and 17.7 in). The tail of a fully grown Verreaux's sifaka grows to be between 56 and 60 cm (22 and 24 in) long. In weight, adult females reach 3.4 kg (7.5 lb) on average, and adult males 3.6 kg (7.9 lb).
Verreaux's sifaka has a relatively low, flat braincase. The face is broader than that of most other indriids, but its snout is reduced. This species of sifaka is also distinguished by its unique dentition. Its dental formula is 18.104.22.168. The upper incisors are very small and are slightly angled inward towards the gap between I1 and I2. In the mandible, Verreaux's sifaka displays the strepsirhine characteristic: the toothcomb. Formed by the procumbent lower incisor and canine, the toothcomb projects past the front margin of the mouth. P. verreauxi also presents the high, shearing molar crests of a folivore, helping to shread the leaves, fruit and flowers that it eats.
Postcranially, Verreaux's sifaka has a low intermembral index that ranges from 63-66. It has a broader ribcage than most other prosimians, and has many lumbar vertebrae lending it considerable flexibility. The pelvis is high and narrow and the acetabulum is relatively shallow, also allowing for greater flexibility. Like other indriids, P. verreauxi has a short calcaneus, pointed nails, and slightly webbed hands and feet.
Verreaux's sifakas forage for food with their troop, primarily in the morning and late afternoon, so they can rest during the hottest part of the day. They are herbivores; leaves, fruit, bark and flowers are typical components of the diet. However, they are mostly folivorous (leaves represent the majority of the diet over the year, especially in the dry season) and they seem to choose food items based on quality (lower tannin content) rather than on availability.
Verreaux's sifakas are diurnal and arboreal, and engage in sunbathing with outstretched arms and legs. They move through the trees by clinging and leaping between vertical supports. They are capable of making remarkable leaps through the trees - distances of 9–10 m are not uncommon. On the ground, they hop bipedally. They live in family groups, or troops, of 2-12, which may consist of one male and female, or many males and females together. Group and population sex ratio can be more or less skewed toward males. Many groups seem to be effectively harem groups with a single dominant male unrelated with resident female(s). They have a home range of 2.8 to 5.0 ha, and although they are territorial, they defend food sources rather than territorial boundaries, as often boundaries overlap. Females are dominant over males, forming a matriarchal society.
Females use anogenital secretion mainly for territory demarcation whereas males seem to use specialized secretions (via anogenital and throat glands) more for sexual "advertisement" than for territorial purposes. Males show bimorphism, by showing either a clean or stained chest, derived from throat gland secretions and smeared on surfaces by rubbing the upper part of the chest. Stain-chested males engage in the most active marking, and chest staining seems to be related to testosterone levels.
Males and females were found to engage in a biological market, exchanging grooming for grooming during the non-mating period, and grooming ("offered" by males) for reproductive opportunities (sexual access "offered" by females) during the mating period. A study found that females copulate more with stained-chested than with clean-chested males. On the other hand, clean-chested males, with a lower scent-releasing potential, usually offer more grooming to females. This “grooming for sex” tactic allows males with a clean chest to get to copulate with females, even if at low rate.
It has also been discovered that sifaka dyads often engage in post-conflict reunions after aggressive episodes: reconciliation occurs more frequently when food is not involved and for low intensity aggressions. In this species play behavior persists into adulthood where it is used, especially by stranger males during the mating period, as an ice-breaking mechanism to reduce xenophobia.
A study of sifaka vocalizations found that roaring barks are associated with anti-raptor responses in which the Verreaux sifakas looked up and climbed down. On the other hand, the meaning of "tchi-fak" vocalizations and growls varied by population, where a population subject to significant terrestrial predation associated these vocalizations with anti-terrestrial responses in which the sifakas looked down and climbed up, while another population associated the "tchi-fak" with a non-specific flight response, and the growl with mild disturbance.
Around 45% of females breed each year when in oestrous between late January and early February. Females give birth to one infant after a gestation period of 130 days, between June and August. For the first 6–8 weeks, the infant clings to the mother's stomach, but for the following 19 weeks, it clings to her back. About 30% of infants are lost to predation by the Fossa (Cryptoprocta ferox) and a smaller number to raptors like the Madagascar harrier-hawk (Polyboroides radiatus).
Those that do survive reach sexual maturity between 3–5 years. Males generally leave the group to join a neighboring group while adult females tend to stay with their natal group.
Ecology and conservation status
The species is listed in CITES Appendix I, and its IUCN conservation status was updated to Critically Endangered in 2020. In the small spiny forest fragments of South Madagascar, sifaka abundance appears to be influenced by the proportion of large trees (diameter at breast height >=5 cm) and by the abundance of the plant species Allouadia procera, a key species of the spiny forest habitat. A long-term, large-scale demographic study of the species at Beza Mahafaly Special Reserve in southwest Madagascar found that the sifaka population there had a population growth rate of 0.98 (with confidence intervals spanning 1), suggesting that the population was not in danger of imminent extinction. However, both severe droughts and an increased annual variation in rainfall levels can depress the population growth rate.
- Louis, E.E.; Sefczek, T.M.; Bailey, C.A.; Raharivololona, B.; Lewis, R.; Rakotomalala, E.J. (2020). "Propithecus verreauxi". IUCN Red List of Threatened Species. 2020: e.T18354A115572044. doi:10.2305/IUCN.UK.2020-2.RLTS.T18354A115572044.en. Retrieved 19 November 2021.
- "Checklist of CITES Species". CITES. UNEP-WCMC. Retrieved 18 March 2015.
- Groves, C. P. (2005). Wilson, D. E.; Reeder, D. M. (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press. p. 121. ISBN 0-801-88221-4. OCLC 62265494.
- Rowe, N. (1996). The Pictorial Guide to the Living Primates. Pogonias Press. p. 49. ISBN 0-9648825-0-7.
- Ankel-Simons, F. (2007). Primate Anatomy (3rd ed.). San Diego, California: Academic Press. pp. 94–95, 358. ISBN 978-0-12-372576-9.
- Norscia, I.; Carrai, V.; Borgognini-Tarli, S.M. (2006). "Influence of Dry Season and Food Quality and Quantity on Behavior and Feeding Strategy of Propithecus verreauxi in Kirindy, Madagascar". International Journal of Primatology. 27 (4): 1001–1022. doi:10.1007/s10764-006-9056-x. S2CID 38305251.
- Wunderlich R.E., Lawler R.R., Williams A.E. 2011. Field and experimental approaches to locomotor ontogeny in Propithecus verreauxi In Primate Locomotion: Linking Field and Laboratory Research. K.D. D'Aout, E.E. Vereecke (eds.) Springer Science. pp.135–154
- Lawler R.R. (2006). "Sifaka positional behavior: Ontogenetic and quantitative genetic approaches". American Journal of Physical Anthropology. 131 (2): 261–271. doi:10.1002/ajpa.20430. PMID 16596593.
- Richard, A.F. (1985). "Social boundaries in a Malagasy prosimian, the Sifaka (Propithecus verreauxi)". International Journal of Primatology. 6 (6): 553–568. doi:10.1007/BF02692288. S2CID 45299922.
- Norscia, I.; Palagi P. (2008). "Berenty 2006: Census of Propithecus verreauxi and possible evidence of population stress". International Journal of Primatology. 29 (4): 1099–1115. doi:10.1007/s10764-008-9259-4. S2CID 19241893.
- Kappeler, P.M.; Schäffler, L. (2007). "The lemur syndrome unresolved: extreme male reproductive skew in sifakas (Propithecus verreauxi), a sexually monomorphic primate with female dominance". Behavioral Ecology and Sociobiology. 62 (6): 1007–1015. doi:10.1007/s00265-007-0528-6.
- Lewis, R.J. (2005). "Sex differences in scent-marking in sifaka: Mating conflict or male services?". American Journal of Physical Anthropology. 128 (2): 389–398. doi:10.1002/ajpa.20206. PMID 15795894.
- Lewis R.J. (2006). "Scent marking in Sifaka : No one function explains it all". American Journal of Primatology. 68 (6): 622–636. doi:10.1002/ajp.20256. PMID 16715510. S2CID 11806179.
- Lewis R.J. & van Schaik C.P. (2007). "Bimorphism in Male Verreaux's Sifaka in the Kirindy Forest of Madagascar". International Journal of Primatology. 28: 159–182. doi:10.1007/s10764-006-9107-3. S2CID 22773229.
- Lewis R.J. (2009). "Chest Staining Variation as a Signal of Testosterone Levels in Male Verreaux's Sifaka". Physiology & Behavior. 96 (4–5): 586–592. doi:10.1016/j.physbeh.2008.12.020. PMID 19162056. S2CID 11419343.
- Norscia, I.; Antonacci, D.; Palagi, E. (2009). Brosnan, Sarah Frances (ed.). "Mating First, Mating More: Biological Market Fluctuation in a Wild Prosimian". PLOS ONE. 4 (3): e4679. Bibcode:2009PLoSO...4.4679N. doi:10.1371/journal.pone.0004679. PMC 2650411. PMID 19262737.
- Dall'Olio S.; Norscia I.; Antonacci D.; Palagi E. (2012). Proulx (ed.). "Sexual Signalling in Propithecus verreauxi: Male "Chest Badge" and Female Mate Choice". PLOS ONE. 7 (5): e37332. Bibcode:2012PLoSO...737332D. doi:10.1371/journal.pone.0037332. PMC 3355113. PMID 22615982.
- Palagi, E.; Antonacci, D.; Norscia, I. (2008). "Peacemaking on treetops: first evidence of reconciliation from a wild prosimian (Propithecus verreauxi)". Animal Behaviour. 76 (3): 737–747. doi:10.1016/j.anbehav.2008.04.016. S2CID 53155723.
- Antonacci, D.; Norscia, I.; Palagi, E. (2010). Iwaniuk, Andrew (ed.). "Stranger to Familiar: Wild Strepsirhines Manage Xenophobia by Playing". PLOS ONE. 5 (10): e13218. Bibcode:2010PLoSO...513218A. doi:10.1371/journal.pone.0013218. PMC 2951354. PMID 20949052.
- Fichtel, Claudia; Kappeler, Peter M. (2011). "Variation in the Meaning of Alarm Calls in Verreaux's and Coquerel's Sifakas (Propithecus verreauxi, P. coquereli)". International Journal of Primatology. 32 (2): 346–361. doi:10.1007/s10764-010-9472-9. PMC 3047677. PMID 21475394.
- Garbutt, Nick (1999). Mammals of Madagascar. New Haven: Yale University Press. ISBN 0-300-07751-3. OCLC 41158604.
- Richard A.F. (1976). "Preliminary observations on the birth and development of Propithecus verreauxi to the age of six months". Primates. 17 (3): 357–366. doi:10.1007/bf02382791. S2CID 28469514.
- Norscia, I.; Palagi, E. (2011). "Fragment quality and distribution of the arboreal primate Propithecus verreauxi in the spiny forest of south Madagascar". Journal of Tropical Ecology. 27: 103–106. doi:10.1017/S0266467410000519. S2CID 86626320.
- Elmqvist, T.; Pyykonen, M.; Tengo, N.; Rakotondrasoa, F.; Rabakonandrianina, E.; Radimilahy, C. (2007). Somers, Michael (ed.). "Patterns of Loss and Regeneration of Tropical Dry Forest in Madagascar: The Social Institutional Context". PLOS ONE. 2 (5): e403. Bibcode:2007PLoSO...2..402E. doi:10.1371/journal.pone.0000402. PMC 1853233. PMID 17476324.
- Lawler R.R.; Caswell H.; Richard A.F.; Ratsirarson J.; Dewar R.E.; Schwartz M. (2009). "Demography of Verreaux's sifaka in a stochastic rainfall environment". Oecologia. 161 (3): 491–504. Bibcode:2009Oecol.161..491L. doi:10.1007/S00442-009-1382-1. PMID 19636591. S2CID 22677169.