Tarsiers are small primates found in Philippines, Indonesia, and Malaysia. They used to be more widespread but have gone extinct everywhere else. The
There are 8 recognized species of tarsier.
The head and body range from 10 to 15 cm in length, but the hind limbs are about twice this long (including the feet), and they also have a slender tail from 20 to 25 cm long.
The weight at most 150 grams.
Their name comes from their huge tarsal bones (basically their heel bones).
Their fingers are also elongated, with the third finger being about the same length as the upper arm. They’re also padded, like a cat.
Even though they are super tiny, their gestation period is very long: 6 months. And they give birth to a single baby. (for comparison, brown rats are twice as big as your average tarsier and their gestation period is just 3 weeks. But tarsiers are born much more developed than rats)
The baby is born large, furred and with open eyes and can climb from day 1. They’re born weighing about 20-30% of their adult weight (it’s like a woman giving birth to Lassie)
The babies start jumping when they’re just one month old and start hunting as soon as they’re able to leap.
Despite being great jumpers, tarsiers don’t usually climb very high. Most species live at heights of between 1 and 2 meters.
They’re also known as owl monkeys due to their huge eyes.
Eyes
Their eyes are the most interesting thing about these primates. They’re nothing like any other primate on Earth.
The eyes can be up to 16mm in diameter. Each one of them is as big as their brain.
Their eyes are so big that they can’t move inside the eye socket. But their necks are very flexible and can rotate 180 degrees in each direction.
Their ears can also move independently to help them hone in on the source of a sound.
According to Wired up to 20% of people can wiggle their ears.
Their eyes are huge because they need large retinas to see in low-light. Tarsiers are nocturnal insectivorous animals, and being able to spot small insects at night is crucial to their survival.
Most nocturnal animals have a layer of crystal at the back of the eye that reflects light back to the retina. It is called tapetum lucidum, and it’s the reason why cat eyes look so bright at night. Tarsiers don’t have this, which is clearly a disadvantage for a nocturnal animal.
To make up for that they have a fovea, which is a little pit in the retina super packed with cones. It is used for sharp central vision. When you read this the words are hitting your fovea. This is uncommon in mammals, only primates have this.
The reason for all of this weird adaptations is that vast majority of primates, including the tarsier ancestors, are diurnal. They hunt and forage during the day and sleep at night. The tarsier at some point became nocturnal, so their eyes had to adapt to their new behaviour.
Hunting
Tarsiers are great jumpers and use their jumping range to pounce on prey.
They can jump 40 times their body length, reaching over 5 meters in one leap.
These huge leaps are usually for fleeing or traveling. When hunting, they seldom pounce on a prey item that’s farther away than 60cm.
Because of their sharp teeth and their great leaping ability, you can say they’re basically arrows with eyes.
They’re the only primate that doesn’t eat any plants at all.
As a side note, this makes them extremely difficult to keep in captivity. They have very specific nutritional requirements.
The majority of its prey are insects, but they will eat any animal they can catch, including birds and bats.
Up to a third of their prey is caught in midair (pretty badass, hope to find footage of this)
To catch insects at night they also use their hearing. They have great directional hearing and they can hear the very high pitched noises that insects make. In fact, the philippine tarsier has a high frequency cutoff of roughly 75-90 Khz, which is the highest of all primates among the highest among all mammals. We, due to decades of headphone use and rave-going, have a cutoff of about 15 Khz. (Kids can hear up to 20 Khz but it deteriorates over time. Humans, elephants and naked mole rats are the only mammals that can’t hear anything over 20 khz)
The reason they can hear such high pitched noises is because they have a structure in their ears called the bony lamina. That’s what allows bats and dolphins to communicate ultrasonically.
Tarsiers are unique because they have bony laminae but also have developed long cochleas, which allows them to hear low noises as well.
Behaviour
Tarsiers are solitary animals, a rare trait among primates.
One looking for better hunting grounds, females often successfully displace males.
All the species of tarsier are vulnerable to extinction due to habitat destruction.
Tarsiers can have mated pairs, meaning a male and female sharing a territory but seldom interacting. In some species, mated pairs will sing a duet at the end of the night.
They communicate vocally and olfactory. They use urine to mark territory. But they also have scent glands in their lip, abdomen, and anus for olfactory communication.
