PALE FORK-MARKED LEMUR
Geographic Distribution and Habitat
The pale fork-marked lemur (Phaner pallescens), also known as the western fork-marked lemur or pale fork-crowned lemur, is a lemur endemic to the dry western forests of Madagascar. They have the largest range of any of the fork-marked lemurs (those of the genus Phaner), and are distributed in patches from the Fiherenana River to the village of Soalala. The most northern populations are more isolated than the rest, and it’s possible that they may actually be a distinct species or subspecies. Pale fork-marked lemurs are dependent on a few rare tree species for food, and they require continuous canopy coverage. Their reliance on these few tree species coupled with their extremely low reproductive rates means that they are very susceptible to disturbance, and sadly this is reflected in their dwindling population size. Pale fork-marked lemurs are the best studied of the four fork-marked lemur species, which sadly isn’t saying much: there is a severe lack of data and research concerning this unique genus.
Previously regarded as a subspecies of Masoala fork-marked lemurs (Phaner furcifer), pale fork-marked lemurs were elevated to full species status in 2001.
Size, Weight, and Lifespan
Pale fork-marked lemurs are about 9–11 inches (23–29 cm) long from head to rump, with their tail adding another 11–15 inches (29–37 cm). They weigh between 11 and 18 ounces (300–500 g). The typical lifespan of a fork-marked lemur is about 12 years in captivity, and slightly less in the wild.
The soft or spongy tissue of a plant or fruit, which is usually white or pale in color (i.e., the white part between the skin and fruit of an orange).
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Fork-marked lemurs get their name from the black forked strips that extend from their nose, over their eyes, and down their back. Pale fork-marked lemurs, as their name implies, are the palest of the fork-marked lemur species. Their hair is mostly light with a silvery sheen, getting lighter towards their belly and darker towards their hands and feet. Like many other nocturnal prosimians, they are small and have large, protruding eyes that allow them to gather as much light as possible in the dark forest environment.
Their nails are pointed, which helps them to grip onto smooth-barked tree trunks. Their teeth are unique as they have what’s known as a “tooth comb”—a row of incisors that are very long and narrow, and that point forward. They use this to scrape out gum that oozes from trees. Their long tongue also helps them to consume these gums and saps.
Like other forked-marked lemurs, the pale fork-marked lemur’s diet is composed primarily of tree exudates like sap and tree gums. Eight-five percent of their foraging time is devoted to finding and eating these foods. They supplement this diet with insects, fruits, flowers, and nectar. They rely heavily on just five tree species with the most protein-rich gums. The trees are rare and distributed patchily, so the lemurs’ survival is highly contingent on the availability of these trees. There is almost never more than one lemur feeding from the same tree at the same time, as they are highly competitive over food trees. Even mated pairs are almost never found foraging near each other.
Behavior and Lifestyle
Pale fork-marked lemurs are nocturnal, meaning that they are active at night and sleep during the day. Arboreal (tree-dwelling), they are typically found in trees at about 10 to 13 feet (3–4 m), although they may travel on the ground or climb as high as as 33 feet (10 m) up trees. They sleep very high in the trees to avoid competition for sleeping sites with other nocturnal lemurs, sometimes using leaf nests made by Coquerel’s giant mouse lemurs (Mirza coquereli).
Pale fork-marked lemurs wake just before dusk and are most active in the first hour after sunset. They move about quadrupedally (on all fours) and are known for their quick movements—which can differentiate them from other, more slow-moving nocturnal prosimians in the dark—and their unique propensity for bobbing their heads.
Fork-marked lemurs and needle-clawed galagos (those of the genus Euoticus) are excellent examples of convergent evolution. They have remarkably similar anatomy, behavior, and ecology. Both are small, nocturnal primates that specialize in eating tree gum. Despite these similarities, their ranges are about 3,000 miles (4,800 km) apart—about the width of the continental United States—and they are only distantly related!
Pale fork-marked lemurs are known to bob their heads regularly. It’s unknown why they do this. Researchers studying these animals use this to help differentiate pale fork-marked lemurs from other similarly-sized prosimians in the dark nighttime forest.
Pale fork-marked lemurs live in monogamous pairs with their offspring. They are not particularly social with any other lemurs besides their mate and young. They defend a well-defined territory of 7–25 acres (3–10 ha) in size. Only about 20% of their waking time is spent within 80 feet (25 m) of their mate, to avoid feeding competition. Females are dominant over males, getting priority access to feeding sites and being dominant in encounters with unknown males.
Pale fork-marked lemurs are highly vocal and emit four calls, which researchers have labeled the “hon,” “ki,” “kiu,” and “kea” calls. They are able to distinguish these calls from the very similar calls of other fork-marked lemur species. Olfactory communication is also very important as they aggressively defend their territories. Males have a large throat gland under their skin that they rub on the head, shoulders, and back of females during grooming. Grooming is common between mates and with offspring, and body posturing is also likely an important form of communication for pale fork-marked lemurs.
Pale fork-marked lemurs mate in October and November each year, and babies are born a few months later in January and into early March. Females are only in estrus for 3 to 4 days of the year, so they have an extremely narrow window in which they are able to become pregnant. It follows that their reproductive rates are very low, with each female producing an average of 0.3 babies each year. In other words, the average female has a baby only about once every three years. Babies are mostly cared for by their mother, who carries them first on her belly then, when they are slightly older, on her back. Males may play some role in caring for offspring as well.
Pale fork-marked lemurs are likely predated by carnivorous mammals such as fossas, as well as snakes and birds of prey, such as the Madagascar buzzard and Madagascar cuckoo-hawk. They have a unique ecological role due to their reliance on five rare tree species that they are largely dependent on for food.
The International Union for Conservation of Nature lists pale fork-marked lemurs as Endangered (IUCN, 2014), appearing on the IUCN Red List of Threatened Species. In 2008, they were assessed as Least Concern—although it’s likely they were in decline at that point; there was a serious lack of data and information available about them at the time. Their latest assessment is based on a suspected population loss of more than 50% over the last 21 years, or about three generation times. Their primary threats are a decline in quality and area of habitat due to charcoal production, illegal logging, and burns to create land for agriculture. These causes are expected to continue as they are very difficult to reverse. Without immediate and significant conservation action, an additional 50% decline is expected in pale fork-marked lemur population over the next 21 years. Their population densities have likely also taken a sharp decline. In 1993 in the Tsimembo forests, their density was estimated at 770–1000 individuals per square mi (300–400 individuals per square km). In 2018 in the Zombitse National Park, their population density was estimated at just 8.5 individuals per square mile (3.3 individuals per square km). While population density naturally varies geographically, such a stark contrast is an indication of significant population decline. Pale fork-marked lemurs are very sensitive to threats because of their low birth rates and their reliance on just five rare tree species.
Madagascar has seen a shocking amount of deforestation over the last several decades. More than a third (37%) of the forest cover on the island was lost between 1973 and 2014. The remaining forest is severely fragmented, with nearly half (46%) of the forest located less than 330 feet (100 m) from the forest edge, a death sentence for the many species that rely on dense, unfragmented swaths of forest habitat.
Climate change is also a potential threat to pale fork-marked lemurs. Climate change shifts the distribution of many plant species. They may move north or south, uphill or downhill. Additionally, changing temperatures and precipitation patterns may change plants’ “timelines,” causing them to flower sooner or later in the year, have shorter fruiting periods, and many other changes. Even seemingly insignificant changes, perhaps imperceptible to humans, could have profound ecological impacts. For a species like pale fork-marked lemurs that are extremely dependent on just a handful of tree species for survival, even slight ecological changes could spell disaster.
Pale fork-marked lemurs are listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival. They are found in several protected areas, including Tsingy de Bemaraha Strict Nature Research, Kirindy Mitea National Park, and Andranomena Special Reserve. There is a serious need for further research to better understand pale fork-marked lemurs.
- Ettinger, A.K., Buonaiuto, D.M., Chamberlain, C.J., Morales-Castilla, I. and Wolkovich, E.M. 2021. Spatial and temporal shifts in photoperiod with climate change. New Phytol. 230: 462-474. https://doi.org/10.1111/nph.17172
- Forbanka, D.N. 2018. Population surveys of fork-marked dwarf lemurs and needle-clawed galagos. Primates. 59: 355–360. https://doi.org/10.1007/s10329-018-0669-4
Written by K. Clare Quinlan, August 2022