TARSIER BEHAVIOR: SOCIALIZING, MOBBING AND MATING

TARSIER BEHAVIOR

Tarsiers (Tarsiidaetarsiers) are bizarre-looking, lemur-like primates. About the size and shape of an African bush baby or small chipmunk and found only in the rainforests and jungles of Borneo, Indonesia and the Philippines, they have enormous eyes and a gremlin-like smile and can rotate their head nearly 360̊. They forage for food at night and are particularly fond of eating cockroaches Tarsiers are found only in some rainforest in some parts of the Philippines and Indonesia.

Tarsier are arboreal (live mainly in trees), scansorial (able to or good at climbing), nocturnal (active at night), crepuscular (active at dawn and dusk), saltatorial (adapted to leaping), motile (move around as opposed to being stationary), sedentary (remain in the same area), territorial (defend an area within the home range), social (associates with others of its species; forms social groups), and have dominance hierarchies (ranking systems or pecking orders among members of a long-term social group, where dominance status affects access to resources or mates).[Source: Tanya Dewey and Phil Myers, Animal Diversity Web (ADW) /=]

Tarsier are and classified as vertical clingers and leapers. Other modes of locomotion include hopping, quadrupedal (use all four limbs for walking and running)ism, and cantering. Tarsiers spend nearly all of their time in trees and are primarily nocturnal. During the day they usually sleep on vertical tree branches or in the hollow of an old tree. They don’t build nests. Vocalizations include loud shrieks in battles over territory and loud duets between separated males and females.

Sharon Gursky-Doyen wrote in Natural History magazine, Spectral tarsiers “use their urine and various body glands to scent-mark along the boundaries of their home range; they announce their claim with early family choruses; and they vocally confront and chase any members of neighboring groups that threaten to intrude. They exhibit tremendous attachment to a particular site, with individuals and sometimes family groups continually using the same sleeping tree for years. Like many territorial primates, spectral tarsiers return to the same tree when it is time to sleep. They prefer hollowed-out fig trees with multiple entrances and exits. These typically form when a "strangler" fig tree grows around another tree, kills it, and the dead supporting tree rots away, leaving an empty space. In measuring the diameters (at "breast height," 4.5 feet aboveground) and heights of their sleeping trees, I was able to demonstrate that individuals residing in larger sleeping trees were more likely to be found at the same site in later years, while individuals residing in smaller trees were more likely to move. I also discovered that polygynous groups were more likely to have the larger sleeping trees. [Source: Sharon Gursky-Doyen, Natural History magazine, October 2010]

Tarsier Social Behavior and Groups

Tarsiers are found mostly in pairs or groupings of up to eight animals. A tarsier pair occupies a territory of around one to two hectares. ocialization includes grooming each other, scent marking, vocalizing (including duetting), and playing. Males travel longer distances and occupy a larger area, while females hunt more efficiently and consume more insects. Group members mark their territories with urine and scents from various glands. Even so there seems to be a great deal of overlapping of territories. [Source: Sabrina Archuleta, Animal Diversity Web (ADW) /=]

Tanya Dewey and Phil Myers wrote in Animal Diversity Web: Most species live in small social groups, sometimes of just a single male and female but often consisting of a single, dominant male, several females, and their dependent young. Western tarsiers (Tarsius bancanus) seem to be more solitary. Tarsiers are mainly seen alone during their active, nocturnal phase, but often sleep with other individuals during the day, although some species rest alone as well. Social groups and individuals defend territories with scent marking and vocalizations. Scent marks can be quite consistent in some species, indicating very stable home ranges. Males generally have larger home ranges that overlap with those of several females. When social groups get together, they may spend time grooming each other. [Source: Tanya Dewey and Phil Myers, Animal Diversity Web (ADW) /=]

Based on available information from some species, male tarsiers generally have larger home ranges that overlap with those of several females. Males sometimes rest during the day with of one or several females. Social group members may help to care for offspring.

Tarsier Family Groups

Sharon Gursky-Doyen wrote in Natural History magazine, “A majority of the sexually mature adults are monogamous, and mates often stay together for most of their lives, which average seven years. With their immature offspring (as many as two per female) they occupy home territories in small family groups. Although direct paternal care is rare, it is common for a member of the group other than the mother — typically an adolescent sister of the infant — to help with the caretaking. Examples of such "allomothering" include sharing food, babysitting, grooming, and playing. An adolescent female will also transport a young infant by mouth if, say, it falls out of a tree where the mother parked it. [Source: Sharon Gursky-Doyen, Natural History magazine, October 2010]

“How might those patterns of behavior have evolved? When I surveyed the primate literature, I found that three main factors had been hypothesized to lead to sociality, or gregariousness, in primates. One is intanticide: if outsiders of their own species pose a threat, relatives stick together to defend their offspring. Another is food abundance: the patchier the distribution of food in the habitat, the more a group may need to come together to share and defend their resources. And finally there is pre dation pressure: members of a group cooperate to warn and defend against common enemies.

“Infanticide has been observed in captive tarsiers, but does infanticide — or the threat of it — play a role in wild tarsier sociality? I kept track of how much time males spent near females, noting whether or not the females were pregnant or lactating. When a female was lactating — that is, had an infant — the average distance between the male and female of a pair was significantly less than when the female was pregnant or at some other point in her cycle: 85 feet versus 135 feet. By remaining near and traveling with the female and the new infant, her mate could prevent neighboring males from getting too close and killing the infant.

“Given the exceptionally large prenatal investment tarsier females must make, it is not surprising that males must help protect the infant. Newborn infants weigh about a third of the mother's weight — imagine a 120-pound woman producing a 40- pound baby! However, the presence of an infant only explained a small proportion of the gregariousness exhibited by spectral tarsiers, since the majority of social interactions did not involve infants.

“I therefore began examining the role of food abundance. I found that individual tarsiers were more likely to remain near other group members when insect abundance was high rather than low: the average distance between group members was 87 feet compared with 175 feet. Although the level of sociality was increased by food availability, as it was by the presence of an infant, it did not even come close to the coordinated mobbing behavior” when a predator is present.

Tarsier Vocalizations and Ultrasonic Songs

Tarsiers engage in duets (joint displays, usually between mates, and usually with highly-coordinated sounds) and choruses (joint displays, usually with sounds, by individuals of the same or different species). Individuals often vocalize at dawn and dusk and duetting and chorusing are common among members of social groups. Vocalizations at dawn and dusk may represent times when individuals are departing from or arriving at communal resting areas. The majority of their nocturnal, foraging time may be spent alone. Some species are relatively silent except for inter-individual contact calls. [Source: Tanya Dewey and Phil Myers, Animal Diversity Web (ADW) /=]

Tarsiers are among the few dozen species regarded as singers. To make this list and animal has to be able to repeat several series of notes in a recognizable temporal pattern. Tarsier vocalizations include high pitched whistles and chattering melodies. High-pitched whistles are varied from simple calls to predator warnings. Some tarsiers have distinct vocalizations to mob, or ward off, a predator. The duet vocalizations are likely a mating call to lead males to females. Other singer species include titi monkeys of South America, a lemur from Madagascar called the indris, and all 20 species of gibbon. [Source: Sabrina Archuleta, Animal Diversity Web (ADW) /=]

Tarsiers can make sounds beyond the range of human hearing. Josie Garthwaite wrote in Discover: “A saucer-eyed Philippine tarsier opens its mouth wide, squints, and lets out a great burst of . . . silence. The gape-mouthed expression of these primates has long been considered an act of yawning or stretching. But Sharon Gursky-Doyen, a biological anthropologist at Texas A & M University, became convinced the pint-size creatures were actually making ultrasonic screeches. She set up microphones at the Philippine Tarsier Sanctuary and found the animals were emitting sounds up to 75 kilohertz; humans cannot hear past 20 kilohertz. “It was mind-boggling,” she says. “It makes you reevaluate everything you’ve done, heard, and observed.” The shrill call may serve as an alarm signal that is undetectable to approaching predators. [Source:Josie Garthwaite, Discover, October 29, 2012]

Tarsier Reproduction

Tarsiers are usually monogamous (have one mate at a time) but also sometimes polygynous (males have more than one female as a mate at one time). They engage in seasonal breeding and year-round breeding. Most tarsier species seem to reproduce seasonally. Among the few species for which there is information, births peak or occur at the end of the rainy season (generally between February and July but varies regionally). Tarsier females go into estrus for one to three days every 18 to 27 days. An unusual characteristic about tarsier mating behavior is why some individuals choose to be monogamous and others polygynous. Few species have such a variable mating system. Some evidence also suggests that a portion of males are not reproductively active and may represent "spare" males that cannot compete with dominant, reproductively active males. [Source: Tanya Dewey and Phil Myers, Animal Diversity Web (ADW) /=]

Pairs of female and male tarsiers stay together to form close bonds for at least 15 months. In general, tarsier females give birth after a long gestation period. The rate of fetal and postnatal development of tarsiers is among the slowest of all mammals.

Sabrina Archuleta wrote in in Animal Diversity Web: Tarsiers have two mating seasons, in six month intervals. They exhibit mating calls referred to as "duets" to find and monitor mate ranges. All species designate a spot to roost in dense vegetation, usually either in pairs or groups. Occasionally young males seeking a group or mate will be alone for a period of time. Some species that stay in groups will let males join. Other species form groups that are exclusively male or female, and the two sexes only come into contact to breed. Females give birth to one offspring at a time. [Source: Sabrina Archuleta, Animal Diversity Web (ADW) /=]

Tarsier Mating Behavior

Before the onset of female ovulation, both male and female tarsiers groom themselves and mark their environment more frequently with urine and feces. Males have been observed to chase after estrous females while chirping like a bird, and they examine female genitals by sniffing. Vocalizations by both sexes also increase in frequency, and include a "piercing-twittering 'chit-chit'". [Source: Liubin Yang, Animal Diversity Web (ADW) /=]

Sharon Gursky-Doyen wrote in Natural History magazine, “While there are a few primate species that vary in their mating patterns, rarely has the variation been observed within a single population, such as that inhabiting the Tangkoko Nature Reserve. Consequently, I wanted to know what led individual tarsiers to choose monogamy or, much less frequently (about 15 percent of the time), polygyny. In some species, the male's help is required in order to successfully rear offspring, and that favors what Devra G. Kleiman, an ethologist and conservation biologist affiliated with the Smithsonian National Zoological Park and the Uni- versity of Maryland, has called "obligate monogamy." But spectral tarsiers don't provide much direct paternal care, so that is not a factor. Why, then, were polygynous groups not more common? [Source: Sharon Gursky-Doyen, Natural History magazine, October 2010]

“Groups that were fortunate enough to possess territories with large fig trees for sleeping sites were significantly more likely to be polygynous than were groups whose sleeping trees were smaller or of another species. While monogamous groups consistently used only one sleeping site, polygynous groups tended to have multiple sites, giving them more options if something were to happen to one of their sleeping trees. That is a significant issue, because tree falls are frequent, owing to the high winds at Tangkoko Nature Reserve and the diffuse root structure of the fig trees. Although fig trees are fairly common within the reserve, those making the best sleeping sites are relatively rare, which is why polygyny is so much less common than monogamy.

“In choosing a mate, a female spectral tarsier apparently looks not only for a male whose mobbing displays demonstrate his readiness to defend her and her offspring against predators, but also, where possible, for one whose territory includes at least one high-quality sleeping site. Why would such a sleeping site — namely a large, hollow fig tree — be so important? One possible ex-plantation is that its numerous entrances and exits provide more avenues of escape if a predator invades.

“My observations of spectral tarsiers suggest that polygyny — one form of sociality — may have arisen in primates when females chose to be with a male that controlled the best territory. A safe sleeping site could be one measure of the "best" territory, but that is only an example. And the tarsiers' mobbing behavior may be comparable to the way their ancestors and other early primates responded to predators. Snakes are persistent predators of modern placental mammals, and according to Lynne Isbell, an anthropologist at the University of California, Davis, they may have been major driving forces of evolutionary change in mammals. Their ability to hunt, moving silently even in the trees , was and remains a major threat to primates. Mobbing behavior may have evolved as a survival tactic in the face of that threat and, in turn, been a major leap toward group living.”

Tarsier Offspring and Child Rearing

Tarsier have a gestation period of around six months, unusually long for such a small animal. Tarsiers give birth to a single young Young are born with their eyes open and are capable of climbing and making short leaps. Tarsier infants can cling to a vertical surface. Female young often stay with their parents until they are adults. Males usually leave when they are juveniles. Tarsiers are cooperative breeders (helpers provide assistance in raising young that are not their own). [Source: Tanya Dewey and Phil Myers, Animal Diversity Web (ADW) /=]

Prenatal development is incredibly slow in western tarsiers. Offspring are born with approximately 60 to 70 percent of the brain mass and 20 percent of the body mass of an adult. Newborn spectral tarsiers have similarly high infant-to-adult weight ratios of 20 to 33 percent. During the pre-birth stage provisioning and protecting are done by females. During the pre-independence stage provisioning and protecting are done by males and females.

According to Animal Diversity Web:Pregnancy is often very costly for female tarsiers. Pregnant females have low mobility, impaired foraging abilities, and maintain smaller home ranges than their non-pregnant counterparts. Furthermore, postpartum females cannot lactate and transport infants at the same time due to energy restrictions. They often "park" their offspring on a secure branch. Pregnant females were observed in a year-round study, and there appears to be no seasonal variation in mating. [Source: Liubin Yang, Animal Diversity Web (ADW) /=]

Females invest heavily in their single offspring through gestation and lactation. Young are born at a precocial stage, able to cling and climb on the day of their birth. In some species the young are cared for by their mother as well as the dominant male of the group and subadult or secondary females. Information on parental Investment in most species is lacking. Young may associate with their parents for a period of time after weaning. Female progeny stay with their parents until adulthood, whereas young males leave during youth. Tarsier mothers and young have been reported to exhibit reciprocal sniffing after birth as a way of recognition. [Source: Liubin Yang, Animal Diversity Web (ADW) /=]

For the first three weeks of an infant tarsier's life, it is common for the mother to carry them in their mouths whenever they move. In pair-bonded species fathers also carry infants in their mouths. While mothers hunt, the infants are often left on a tree branch for intervals of time. In a monogamous pair both parents will visit the infant during this time. In groups other group members might make brief visits to check up on the infant while the mother is away. Once the infant is about a month old it begins hunting on its own, but remains in the group and within visible range. Females often remain in their parental group throughout their life, unless forming monogamous pairs. Males often leave to live alone or join other groups between one to two years of age. [Source: Sabrina Archuleta, Animal Diversity Web (ADW) /=]

Tarsier Mobbing Behavior

Reporting from a mountainside in Tangkoko Nature Reserve on the Indonesian island of Sulawesi, Sharon Gursky-Doyen wrote in Natural History magazine, “All of a sudden I hear high-pitched shrieks from higher up the mountain.... Somewhere a group of tarsiers is upset, and I want to know why. As I get closer to the commotion, I slow down, not knowing what awaits me. Cautiously, I scan the foliage for tarsiers and for whatever threat has caused them to call with such urgency. Then I see it: a large python coiled up in a tight ball. Four, five, no, six spectral tarsiers — each no bigger than my hand — are sounding the alarm. And they are all leaping toward the python. [Source: Sharon Gursky-Doyen, Natural History magazine, October 2010]

“The tiny tarsiers repeatedly lunge so close to the intruder that I think they are about to become snake dinner, and then they leap out of reach. One individual is truly brazen: he jumps onto the python's back and bites it! The snake's muscles ripple as it tries to capture and strangle the animal on its back. But the daring tarsier is too quick, and darts away. For nearly thirty minutes, the tarsiers lunge and retreat; even the individual I was following earlier arrives to join in the mobbing. Finally the python uncurls — it must be twelve feet long — and slithers away. After calling for another twenty minutes the tarsiers move off But they remain skittish throughout the night, breaking out into alarm calls and frequently returning to the scene of the face-off.

“The spectral tarsiers' mobbing of a predator is a total surprise. What might have prompted such brazen — and coordinated — behavior? I know that a male-female pair and two offspring, a juvenile female and an infant, sleep during the day near the site of the incident. But on my nightly "focal follows," the excursions in which I track the activity of one individual, I rarely encounter more than one or two tarsiers in any one place. Yet I've just seen at least six adults join together in attacking a python. Maybe the species is more gregarious than anyone has realized. And the incident is significant in another way: the vast majority of species known to mob predators are diurnal, not nocturnal. [Ibid]

Studying Tarsier Mobbing

Sharon Gursky-Doyen wrote in Natural History magazine, “As you might imagine, interactions between tarsiers and their predators are relatively rare and difficult to observe. I thus looked for ways to mimic the presence of predators. First, I used physical models of predators, such as carved wooden civets, rubber snakes, and plastic birds of prey; and second, I recorded the vocalizations of predators at zoos and then played them back in tarsier territory. [Source: Sharon Gursky-Doyen, Natural History magazine, October 2010]

“In 74 percent of encounters with a rubber python, the tarsiers alarm-called, and in 42 percent of the incidents, once joined by other individuals, they also mobbed the snake. Such an encounter had a measurable effect on their social behavior throughout the night. The average distance between group members when no rubber snakes were present was 135 feet, but when rubber snakes were planted within the group's territory, that distance shrank by about half, to 67 feet. Upon encountering the model bird of prey (a falcon), their response a little more than half the time was to freeze, on average tor twenty-one minutes. On other occasions they both mobbed and alarm-called. And when raptor vocalizations were played back, the tarsiers responded in 42 percent of the experiments by alarm-calling, and in 38 percent by both alarm-calling and mobbing the speakers.

“The model civet often elicited harsh alarm calls, but it was mobbed in only about 10 percent of the encounters. Thinking the experimental setup might be overlooking the tarsiers' well-developed sense of smell, I organized a new set of tests. I observed the reactions of twenty different adults as each was exposed to four different situations: a wooden civet model covered in civet as their bodies, provide balance when the animals leap in their characteristic upright posture. Below: Asian palm civet is a skillful climber and dangerous to the tree-dwelling tarsiers. The author's experiments show the predator's scent, sight, or call may independently elicit tarsier alarm calls and mobbing responses.

“The results were revealing. The tarsiers never ignored the wooden model with civet urine: it provoked alarm calling every time, and they mobbed it in 77 percent of the encounters. In contrast, when exposed to the wooden civet model without urine, the tarsiers responded with alarm calls 39 percent of the time and with both alarm calls and mobbing 15 percent of the time; during 46 per- cent of the trials, they ignored it. In response to the stick with urine, the tarsiers alarm-called during 93 percent of the trials, but never mobbed; they ignored it in 7 percent of the trials. Unsurprisingly, the stick without urine provoked no response at all.

Explanations for Tarsier Mobbing

Sharon Gursky-Doyen wrote in Natural History magazine, “Mobbing is obviously a risky tactic, yet in both sets of experiments, more adult tarsiers mobbed the ostensible predator than resided in the local territory. What drove other adults to get involved? I observed that adult females regularly attended mobbings, but they were usually pas- sive participants, alarm-calling nearby and watching from a safe distance. The aggressive participants, those lunging at the predator and then retreating, were usually adult and adolescent males. That was an important clue. [Source: Sharon Gursky-Doyen, Natural History magazine, October 2010]

“To my knowledge there were a number of common hypotheses to explain mobbing behavior, all some practical, protective outcome, such as driving away the predator.One rationale, known as "infant silencing," suggests that mobbing distracts predators from young offspring, which learn to remain silent during the exchanges. That hypothesis predicts that mobbing will be restricted to groups with young infants. However, I found that mobbing occurred just as often in groups without immature offspring, thus knocking a hole in that explanation. Another idea is that mobbing instills "site avoidance." That is, individuals will avoid a locale where a predator was previously en- countered and mobbed. But tarsier mothers apparently had no qualms about parking an infant in or near a tree where they were previously exposed to a rubber snake. The data did not support that hypothesis.

“According to the "perception advertisement" hypothesis, the potential prey animals, by openly identifying themselves (in this case through mobbing), inform the predator that it has lost the advantage of surprise. Discouraged, the predator then leaves. Naturally, the opportunity to test that was limited to when an actual snake appeared. But based on preliminary observations, the hypothesis fell flat: there was little evidence that the snake spent significantly less time in the area after being mobbed than when the tarsiers only emitted alarm calls or just ignored it. The same set of observations also rejected the "move-on" hypothesis, which states that because it is discomforted by harassment, a predator entering an area will leave sooner the more intensely it is mobbed.

“Finally, the "cultural transmission" hypothesis states that an individual learns to fear an object when it witnesses other animals mobbing it, and thus learns to avoid it or mob it in the future. However, when studying the response of infants, I found that nursing infants, even in their first week of life, alarm-called when exposed to a model snake, despite never having seen a snake previously. Their awareness of danger from snakes was not culturally transmitted, undermining that hypothesis.

“Because none of the above hypotheses seemed satisfactory, I proposed a new one: spectral tarsiers inob predators as a "costly sig- nal." In effect, the signaler advertises that it can afford to perform an otherwise detrimental act — something that a weaker competitor cannot do as effectively. The classic costly signal is the peacock's tail. The tail makes the bird more vulnerable to predators, but the message to the potential mate is, "I have survived in spite of this huge tail, hence I am fitter." Similarly, while aggregating around a dangerous snake, tarsier males may demonstrate their current physical condition, agility, and speed — and therefore suitability as a mate. According to this hypothesis, the trait of mobbing behavior has evolved in males because it is attractive to females, thus increasing a male's chances of procreating. The driving force is a type of natural selection known as sexual selection.

“Because spectral tarsier groups contain only one adult male, any additional males that show up at a "mob scene" must come from other groups. But I observed that males did not show up at all such events. In 80 percent of the cases, including both experimentally elicited and naturally occurring events, males preferred to join groups that contained adolescent females — they came to impress the gals! By observing the males mobbing, young females can evaluate the ability and willingness of males to pro- tect them and their future offspring against predators.

“Mobbing, then, seems to be a way for a male to get an adolescent female to leave her group and form a new pair. That conclusion naturally made me curious about why tarsiers join groups, leave groups, or remain in their parental group. To this end, I started to explore dispersal — the permanent departure of an animal from its original home.

“Because dispersal involves leaving the protection of a familiar group and territory, an animal that takes the plunge increases its risk of predation and takes a gamble on finding food resources. Therefore the payoff needs to be significant. In mammals, males tend to be the ones to seek new territories. One of the most widely accepted explanations for that is the preponderance of polygynous mating systems — one male siring the offspring of several females in a group. In a polygynous group, the females invest more time and energy in their offspring than the male does. Consequently, they usually have a greater stake in a home range proven to have sufficient resources for successful reproduction, and the males are the ones likely to strike out on their own.

Studying Tarsier Mating Behavior

Sharon Gursky-Doyen wrote in Natural History magazine, “Starting in 1994 and continuing through 2008, 1 tracked seventy-four banded individuals, noting their location relative to their initial sleeping trees. Both sexes proved equally likely to disperse from their natal territories, but males dispersed significantly farther than females, an average of 2,165 feet away, compared with 873 feet for females. One possible explanation for the difference in distance may be that it reduces the chances of inbreeding. [Source: Sharon Gursky-Doyen, Natural History magazine, October 2010]

“I decided to examine possible ecological factors, specifically variation in insect abundance, size of home territory, sleeping trees (size and species), and habitat quality (number of trees, number of tree species, number of large trees). After a field assistant and I spent more than a thousand hours following the movements of adult individuals in ten groups, we were able to conclude that polygyny is not limited by insect biomass, insect abundance, or territory size, but primarily by access to high-quality sleeping sites — that is, tall, wide fig trees. Real estate ruled!

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Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated December 2024