Distribution and abundance of Peleng Tarsier (Tarsius pelengensis) in Banggai Island group, Indonesia.

The Peleng tarsier (Tarsius pelengensis) is poorly known primate, with a range limited to Banggai island-group, Central Sulawesi, Indonesia. It was classified as "Endangered" by IUCN in 2017 based on extremely limited demographic and distributional data. The aim of this study was to collect and analyze data on the population and distribution of Peleng tarsiers. Surveys were conducted over approximately 5 months in 2017 and 2018 across Peleng and the neighboring islands of Banggai, Labobo, and Bangkurung. We determined that tarsiers only occur on Peleng and Banggai Island. The average population density in Peleng and Banggai was estimated to be 234 individuals/km2. This is comparable to the broad ranges of tarsier densities throughout Sulawesi and offshore islands. Peleng tarsiers were found in all elevations (0-937 m above sea level) and nearly all vegetated habitats in Peleng island. Using the IUCN criteria for determining conservation status, in conjunction with our new data, we believe that the Peleng tarsier population should be classified as "Vulnerable".

Small, odd and old: The mysterious Tarsius pumilus is the most basal Sulawesi tarsier.

In this study, we present the first genetic evidence of the phylogenetic position of Tarsius pumilus, the mountain tarsier of Sulawesi, Indonesia. This mysterious primate is the only Eastern tarsier species that occurs exclusively in cloud forests above 1800 m.a.s.l. It exhibits striking morphological peculiarities-most prominently its extremely reduced body size, which led to the common name of 'pygmy tarsier'. However, our results indicate that T. pumilus is not an aberrant form of a lowland tarsier, but in fact, the most basal of all Sulawesi tarsiers. Applying a Bayesian multi-locus coalescent approach, we dated the divergence between the T. pumilus lineage and the ancestor of all other extant Sulawesi tarsiers to 9.88 Mya. This is as deep as the split between the two other tarsier genera Carlito (Philippine tarsiers) and Cephalopachus (Western tarsiers), and predates further tarsier diversification on Sulawesi by around 7 Myr. The date coincides with the deepening of the marine environment between eastern and western Sulawesi, which likely led to allopatric speciation between T. pumilus or its predecessor in the west and the ancestor of all other Sulawesi tarsiers in the east. As the split preceded the emergence of permanent mountains in western Sulawesi, it is unlikely that the shift to montane habitat has driven the formation of the T. pumilus lineage.

Nocturnal Primate Communication: Ecology, Evolution and Conservation.

Auditory, visual and olfactory cues play varying roles in non-human primate communication, and these systems have been intensively studied over the last several decades. The use of vocalisations as a primary mode of communication has been the focus of much research, especially in attempts to understand the origins of human language, with a major focus on anthropoid primates and diurnal lemurs. Over the last decade, technological advances have allowed researchers to begin to conduct in-depth investigations into the communication systems exhibited by the nocturnal and cathemeral prosimian primates, including tarsiers, lemurs and lorises. Understanding how nocturnal prosimians use visual, olfactory and auditory cues is vital for reconstructing the origins of primate communication systems. In this special issue, we highlight some of the more exciting advances in the communication strategies of the prosimians. Contributions come from work conducted in Kenya, Tanzania, Senegal, Rwanda, Madagascar and the Indonesian islands of Java and Sulawesi. Topics will include: the description of novel ultrasonic vocalisations, including frequency and function of these newly discovered calls; the possible use of vocalisations to navigate and assemble at sleep sites; the importance of species-specific contact vocalisations for the identification of new species; the use of urinary and glandular signals to communicate and the methods developed to understand this complex communication in the field; the use of vocalisations for niche separation among nocturnal primates from mainland Africa and Madagascar; and whether or not we can use new technologies to discern whether prosimians use vocalisations for individual identification of group members. We discuss the importance of new field methods including novel equipment and techniques, the use of vocalisation to influence conservation practices and the importance of comparing across prosimian taxa to reconstruct the communication systems of our early primate ancestors.

Echolocation in a Nocturnal Primate?

Recently it has been noted that Gursky's spectral tarsier emits ultrasonic calls. Because high-frequency sounds are capable of travelling only short distances, their function is limited by the distance the sound can be discerned. One possible function for these short-distance, high-frequency sounds is that they might be used by the tarsiers to navigate throughout their environment. I conducted this study at Tangkoko Nature Reserve in Sulawesi, Indonesia, from May to August 2017. Using the focal follows, I recorded the start of each locomotor activity to the nearest second. I also simultaneously recorded all ultrasonic vocalisations that the focal individual emitted using a Wildlife Acoustics Ultrasonic Song Meter BAT3. Approximately 42% of the ultrasonic calls that I recorded during this study were given within 1 s prior to engaging in locomotor activity. The tarsiers gave statistically more ultrasonic calls during locomotion than during other behaviours (rest, forage and social). Four types of ultrasonic calls were given while locomoting: whistles, doubles, trills and frequency-modulated calls. Of these, the trill and the frequency-modulated call were only given during locomotion, and trills were only given prior to leaping. These results preliminarily suggest that the tarsiers do use ultrasonic calls for navigation. Studying echolocation in organisms closely related to bats is critical for understanding the evolution of echolocation.

Impact of Typhoon Haiyan on a Philippine Tarsier Population.

Over the last 2 decades the Philippine tarsier (Carlito syrichta aka Tarsius syrichta) has had its conservation status revised from Endangered to Data Deficient to Near Threatened. The last status change was based on a study of the species' population density, which suggested that a single natural catastrophe could potentially wipe out the Philippine tarsier. In 2013 typhoon Haiyan hit Bohol, one of the island strongholds for this species. In this study we compare the density of the Bohol tarsier population within the Philippine Tarsier and Wildlife Sanctuary before and after the typhoon. We demonstrate that the typhoon significantly affected the density of the Philippine tarsier in the sanctuary. Before the typhoon, tarsier density was approximately 157 individuals/km2 whereas after the typhoon the density was a mere 36 individuals/km2. Prior to the typhoon, more Philippine tarsiers were found in older secondary forest than in younger secondary forest, whereas after the typhoon all observed individuals were found in relatively younger secondary forest. Vegetation plots where we observed Philippine tarsiers prior to the typhoon contained a mean of 33 trees/m2, with a mean diameter at breast height (DBH) of 24 cm, and a mean height of 4 m. After the typhoon vegetation plots contained an average of 156 trees, had a mean DBH of 6 cm, and a mean height of 2 m. Based on the IUCN Red List criteria, the reduction and fluctuation in the density of this species suggests that the conservation status of the Philippine tarsier should be changed to Vulnerable. This study indicates natural disasters can have a significant effect on the extinction risk of primates, with implications for future effects of anthropogenic climate change.

Ultrasonic Vocalizations by the Spectral Tarsier, Tarsius spectrum.

Although the vocalizations of spectral tarsiers have been studied for over 3 decades by numerous primatologists, the data in this paper represent the first evidence that this species communicates in the ultrasonic range. In addition, this paper characterizes the types of ultrasonic vocalizations by spectral tarsiers, Tarsius spectrum. Data were collected at Tangkoko Nature Reserve in Sulawesi, Indonesia, from January through April 2013. Recordings were made on a Wildlife Acoustics Ultrasonic Song Meter BAT2 from 10 groups of varying sizes and compositions. The ultrasonic recorder was placed at the base of the group's sleeping tree and recorded from 5.00 to 7.00 h using an omnidirectional microphone. The ultrasonic vocalizations fell into 5 main categories: chirps, twitters, choruses, doubles and whistles. Chirps were the most frequent ultrasonic vocalizations, followed by twitters, choruses, doubles and then whistles. While chirps, twitters and choruses extended from the audible to the ultrasonic range, the doubles and whistles were pure ultrasound. Currently, the function of these ultrasonic vocalizations is not yet clear and requires additional research.

Altitude and forest edges influence the density and distribution of pygmy tarsiers (Tarsius pumilus).

In this study, we examine how high-altitude ecology and anthropogenic edges relate to the density and distribution of pygmy tarsiers. Pygmy tarsiers (Tarsius pumilus) are extremely small-bodied primates (55 g) that are endemic to high-altitude forest and exhibit several differences from lowland Sulawesian tarsier species. From June to September 2010 and January to March 2012, we conducted a population census of pygmy tarsiers across multiple altitudes. Sampling took place within a 1.2 km(2) area encompassing altitudes of 2,000-2,300 m a.s.l. on Mt. Rore Katimbu in Lore Lindu National Park, central Sulawesi, Indonesia. We observed 22 individuals, with an estimated population density of 92 individuals per 100 ha. These results indicate that pygmy tarsiers live at a lower density than lowland Sulawesian tarsier species. Lower density was associated with decreased resources at higher altitudes, including decreased tree size, tree density, and insect biomass. Within the sample area, we found pygmy tarsiers in only 8 of 24 (33%) quadrats, suggesting a nonrandom distribution that probably overinflated this population density estimate. Pygmy tarsiers exhibited a clumped distribution near anthropogenic edges that were associated with increased insect abundance and biomass. Airborne insects were more abundant along forest edges than within the forest interior, and pygmy tarsiers were observed to forage along edges where there was a higher abundance of Lepidoptera and Orthoptera. Tarsiers may mitigate the decreased availability of insects at high altitudes by adjusting their ranging patterns to remain near forest edges.

Population survey of the Philippine tarsier (Tarsius syrichta) in Corella, Bohol.

In 1986, in response to the rapid habitat destruction throughout the archipelago, the Philippine tarsier was classified as endangered. Since that time, this tarsier has been reclassified as data deficient and more recently as near threatened despite a significant lack of information on the population density of the species. Data were collected at the Philippine Tarsier Foundation Sanctuary from June to October 2010. Population density was estimated using a modified form of the quadrat census method. A total of 55 individuals were located within the sampled area. This is equivalent to approximately 1.55 tarsiers per hectare. Ecologically, there were significantly more tarsiers found in the young secondary forest than in areas characterized as old secondary forest. Extrapolating to the entire protected area, as many as 258 tarsiers may reside in the sanctuary. The vegetation plots where tarsiers were found had substantially more trees per plot, contained trees with larger diameters, and contained slightly taller trees than did the plots where no tarsiers were observed.

Function of snake mobbing in spectral tarsiers.

Numerous species are known for their tendency to approach and confront their predators as a group. This behavior is known as mobbing. Snakes seem to be one of the more consistent recipients of this type of predator-directed behavior. This paper explores individual differences (sex and age) in the mobbing behavior of the spectral tarsier toward live and model snakes. This study was conducted at Tangkoko Nature Reserve (Sulawesi, Indonesia) during 2003-2004. During this research, 11 natural mobbing events and 31 artificially induced mobbing events were observed. The mean number of individuals at a mobbing was 5.7. The duration of mobbing events was strongly correlated with the number of assembled mobbers. Adults were more likely than other age classes to participate in mobbings. Males were more likely than females to participate in mobbings. Mobbing groups often contained more than one adult male, despite the fact that no spectral tarsier group contains more than one adult male. No difference in body size between extragroup males and resident males was observed, refuting the "attract the mightier" hypothesis. The number of mobbers did not affect whether the tarsier or the snake retreated first, countering the "move-on" hypothesis. The "perception advertisement" hypothesis was tentatively supported, in that live snakes were rarely seen in the area following mobbing calls, in comparison to when tarsiers either ignored the snake or alarm call.

Associations between adult spectral tarsiers.

While anecdotal observations of gregarious behavior in nocturnal prosimian primates are common, most anthropologists continue to refer to them as solitary, perhaps based on the assumption that the occasional social interactions observed via ad libitum methods represent random chance encounters and not patterned social interactions. In this paper, I test the null hypothesis that nocturnal encounters between spectral tarsier (Tarsius spectrum) group members, outside of the sleeping tree, are the result of chance. Three male-female pairs were radio-collared and observed over a 4-month period, using continuous focal animal sampling at the Tangkoko Nature Reserve (Sulawesi, Indonesia). Using Waser's random gas model, I found that spectral tarsiers spent more time in proximity to other group members than expected by chance, given the size of their home range and nightly path length. Adult group members spent 11% of the night in physical contact and an additional 17% of the night within a 10-m radius of one another. Spectral tarsiers were also observed to significantly increase the amount of time spent foraging when located less than 10 m from another group member. Individuals foraging in proximity to another adult group member had lower insect capture rates compared to individuals who were not foraging in proximity to another adult group member. If living in a group is costly to these tarsiers' foraging efficiency, then why don't they actively avoid one another when foraging? One situation in which it might benefit tarsiers to be gregarious is high predation pressure. Preliminary results suggest that predation pressure by snakes may be the most likely factor selecting for the tarsiers to forage in proximity.

Predation experiments on infant spectral tarsiers (Tarsius spectrum).

In this paper, I investigate how mother and infant spectral tarsiers, Tarsius spectrum, respond to the presence of potential predators. I conducted this study at Tangkoko Nature Reserve in Sulawesi, Indonesia, from June to November 1999. I exposed 2 infants to 3 types of potential predators (large models of birds of prey, large rubber snakes and the vocalizations of large birds of prey) for a total of 18 nights. Infants moved a greater distance from their parked location when exposed to rubber snakes (1.8 m) compared to nights when they were not exposed to potential predators (0.23 m). On the other hand, when large bird of prey models were placed near the parked infant, the infant did not move from its parked locale (0.05 m). Parked infants repeatedly gave alarm calls in response to the presentation of all potential predator types. When an infant produced an alarm call following the presentation of a potential predator, the mother responded with her own alarm call approximately 88% of the time. However, when an infant produced an inappropriate alarm call, the mother responded with her own alarm call only 19% of the time. These results suggest that spectral tarsier infants use alarm calls to ask questions about the things they encounter in their environment. Infants and mothers both produced a twittering alarm call in response to the bird of prey models, whereas they both produced a harsh loud call 3 times in rapid succession in response to the presence of the rubber snakes.