UP Biologists found Philippine Tarsier behaviors that defy expectations, and could suggest a new species.听
Found along the coast of Northern Mindanao, the 50-hectare Initao-Libertad Protected Landscape and Seascape (ILPLS) in Misamis Oriental may seem like an unlikely place to study wildlife. This limestone forest is split into an ecotourism zone with matching infrastructure, bordered by plantations, and sliced in two by a national highway. That makes it not only a fragmented forest, but also a small one, being roughly the size of 鈥渏ust ten Sunken Gardens.鈥�
For a PhD student, Simeon Gabriel 鈥楽ig鈥� Bejar, and his mentor, Dr. Mariano Roy Duya from the UP Diliman Institute of Biology (IB), however, the ILPLS is a laboratory and a playground. Despite its shortcomings, the forest has the advantage of being safe for researchers and is full of large, centuries-old trees with a heavy understorey of vines and liana. That makes it the perfect place for them to study a true national icon, Carlito syrichta or the Philippine tarsier.听
It might surprise people to know that despite its immortalization in Philippine ecotourism, very little is actually known about the Philippine tarsier. According to Bejar, many of our assumptions on their habits and social behavior come from two Bohol and Leyte-centered papers in 2001 and 2002. Duya and his team knew this would not be enough; so, taking inspiration from plans by the late Dr. Perry Ong, they set out to study tarsiers around the country and outside captivity. This would lead them in 2015 to the ILPLS, where Bejar, Duya and their colleagues found tarsiers, as expected. What they did not expect was how strangely these tarsiers would act.
The Philippine tarsier
To preface the group鈥檚 findings, we need a rundown of what we knew about Philippine tarsiers up to that point. While other tarsier species can be found in places like Sulawesi and Borneo, the nocturnal Philippine tarsier is, as the name suggests, found only here.
Like other animals, Philippine tarsiers have a home range, typically 6.45 hectares for males and 2.25 hectares for females. 鈥淭hink of a home range as the whole area where they eat, sleep and mate,鈥� Bejar explained. Scientists generally believe that Philippine Tarsiers are both solitary and territorial; they do not share these home ranges and actively defend them from others.
Within these ranges, they also have 鈥渃ore areas,鈥� or places they predominantly favor over others, such as favorite sleeping spots, which can be found up to 5 meters above ground.
One way to distinguish primate species is how gregarious they are, or in the case of Philippine tarsiers, are not. Tarsier pairs like mother-offspring have occasionally been observed sleeping together, but there has been very little evidence of complex group behavior beyond this. Contrast this with Eastern tarsiers of Sulawesi, which are known for grooming, babysitting, and other 鈥榗aring鈥� behaviors. Male Philippine tarsiers are also not known to give any parental care at all, even when captivity keeps individuals close together.听
Babysitting fathers
What little we did know about Philippine tarsiers was further called into question in late 2024, when Duya, Bejar, and colleagues from the IB and the UP Institute of Environmental Science & Meteorology (IESM) released two papers on the tarsiers of ILPLS in the International Journal of Primatology.
For these studies, Bejar and the team hand-captured or used mist nets to catch eight tarsiers and attach very-high-frequency (VHF) radio tags to them from 2016 to 2018. Using these, team members were able to triangulate the position of each tarsier, extrapolating the sizes of their home ranges and observing how they behaved inside them, particularly in their sleeping sites.
What emerged from their tireless tracking was a description of behavior that diverges from that found in the Bohol-centered literature. 鈥淲hat was most interesting for me was that their home ranges overlapped,鈥� Bejar said of these forest-fragment specimens. Whether this flexibility was an adaptation to a smaller, discontinuous habitat is still unclear; but he thinks these tarsiers might be taking turns in common areas to avoid conflict. This seems to be supported by the fact that while tarsier home ranges overlapped, their core or 鈥榝avorite鈥� areas seemed not to.
Furthermore, unlike tarsiers that typically sleep up to a height of 5 meters, ILPLS tarsiers were observed sleeping in thickets up to 8 meters or more in giant 鈥榗entury trees鈥� that they access through vines. 鈥淭his,鈥� Bejar noted, 鈥渟olidifies the importance of these large trees. It doesn鈥檛 mean that since we used to see them favor smaller trees, that larger trees are not important to their survival. This (behavior) might change depending on their predators or other disturbances in the area and begs the question: what threats or dangers are they avoiding here?鈥�
Last but definitely not least, while their tarsiers were still being observed to be sleeping alone, Bejar and the team also found them in groups of up to four individuals, composed of one adult male, one adult female, and two subadults. The adult female was observed nursing and grooming at least one of the subadults; but, much to their surprise, they also saw the adult male huddling with and babysitting other members of the group.听
This caring and gregarious behavior to what the group believes was its family unit flies in the face of the image of tarsiers, especially adult males, as solitary or absentee parents. Furthermore, this same male was seen paired with another female, suggesting a network of relationships more complex than had been previously imagined.
One or three?
What are the implications of these findings? For Bejar, this level of behavioral flexibility by Philippine tarsiers suggests that there may be not just one species of the Philippine tarsier, but three. It so happens, Bejar said, that tarsiers are 鈥渃ryptic species,鈥� meaning that the morphological differences between them are so fine, you usually need other techniques to tell them apart.
For his PhD, Bejar wants to put this three-species idea to the test, comparing tarsiers from Bohol to Dinagat Island, all the way down to Misamis and Zamboanga Sibugay, based on their calls, physical features, and their genes. 鈥淲e have initial data that suggest that the calls of tarsiers from Misamis have a different frequency from the ones in Bohol,鈥� he said, which makes evidence from techniques in a field called 鈥渂ioacoustics鈥� very important, techniques Bejar hopes to put to good use soon.
Moreover, a 2014 study by Brown and colleagues found clues of species distinction using tarsier mitochondrial DNA markers. Bejar hopes to get more samples and use better genetic markers to build on these findings. 鈥淲hile we can use better DNA markers to definitively say, 鈥榯hese specimens are really different,鈥欌�� he said, 鈥�(evidence from mitochondrial DNA) is definitely enough to say, 鈥榣ook here, we have something here!鈥欌��
Regardless, whether we have one species or three, one might still ask: why care about these details at all? For Bejar鈥檚 mentor, Duya, each publication goes towards standardizing our knowledge on the Philippine tarsier and creating a Species Action Plan for it based on hard science. 鈥�Actually, organizations like the Department of Environment and National Resources (DENR), they have priorities but it鈥檚 hard to determine your actions without a roadmap.鈥� If there are indeed more than one species of Philippine tarsier, you would need taxonomic data, and lots of it, to find out what their needs are and how to best conserve them.
Once we know more about the Philippine Tarsier, Duya hopes that more collaborations can help government and state universities and colleges (SUCs) push forward tarsier research and protect conservation where they are found. 鈥淯P Diliman is just UP Diliman,鈥� he said. 鈥淭here are so many places we want to go to. But once we standardize things, it should be SUCs implementing things in their mangroves and their forests.鈥�
鈥淪o as much as possible, if we can make the science easy for them, we will do it.鈥�
For updates on the research team’s latest discoveries, follow their official Facebook page:
Read their paper on Philippine Tarsier ranging behavior in Misamis Oriental 听
Read their paper on sleeping sites, sleep-related behavior and social systems 听
