The Gursky's Spectral Tarsier is a species endemic to the Indonesian islands of Southeast Asia. Although their fossil relatives have been found in Asia, Europe, North America, and Africa, modern tarsiers are restricted to Pulau Peleng, and Pulau Selajar, although most live on the northern peninsula of Sulawesi Island where they have likely lived for more than 40 million years. Tarsiers evolved from a diurnal, or daytime-dwelling, ancestor, splitting from other monkeys and apes around the time the dinosaurs died out, about 64.2 to 58.4 million years ago. They are found in primary and secondary rainforests, though they prefer secondary growth forests. Their habitat ranges from the lowland evergreen rainforest near sea level to the lower montane rainforest up to 1500 m, although they have also been found in mangroves and scrub forest. These tiny tree-dwellers are among the smallest known primates, and have the biggest eyes of any mammal relative to their body weight. Their head-body length ranges from 9.5 to 14 cm and tail length ranges from 20 to 26 cm, and their eyes are larger than their brain. They have the most acute night vision of all primates, and even if their head is immobile due to large eye size, this is compensated for by the ability to rotate the head 180 degrees. The gestation period is approximately 6 months, and births also usually occur during May or November. Females give birth to a single offspring, which is born fully furred and with its eyes open. Newborns are precocial and are able to climb at just one day of age. Both crepuscular and nocturnal, they are very active throughout the night. At dusk, they travel for about 30 minutes until they find a forage site. They move through the trees and can leap more than 40 times the length of their body. As morning approaches, spectral tarsiers sing as they return to their sleeping sites, either as a duet with their mate or in a family chorus. These songs signal to neighboring groups that a territory is occupied. They mark their territories with urine and glandular secretions. They eat live animals, such as flying insects such as moths, locusts, beetles and cicadas. They occasionally eat small vertebrates, such as lizards or bats. Once a prey item is targeted, a tarsier ambushes its prey with a sudden lunge, grasps it with its long, slender fingers, and bites to kill it. The tarsier then returns to its perch to consume its prey. This form of ambush hunting requires excellent hand-eye coordination. Tarsiers can eat 10% of their own body weight every 24 hours, and they drink water several times throughout the night. Potential predators of spectral tarsiers include arboreal snakes, civets, monitor lizards, humans, owls and other raptors, and feral cats. If a predator, particularly a snake, is identified, they emit an alarm call. This initiates mobbing behavior, in which numerous tarsiers gather and approach the predator as a group, screaming, lunging, and even biting. Mob groups usually consist of adult males from neighboring groups, which is interesting as most spectral tarsier social groups only contain one territorial adult male. This grouping by neighboring males suggests some form of cooperation among males during predator mobbing. The species is still considered vulnerable due to habitat destruction caused by logging. Logging reduces tarsier densities through the destruction of preferred sleeping sites such as strangler fig trees. Strangler figs are removed from human-utilized forests because they are seen as a threat to other commercially valuable trees. This bleak situation indicates that some primate species in Sulawesi may go extinct before they have even been identified.