7. Reproduction and Lifespan

7.1 Mating

Sloths reach sexual maturity when they’re between one and two years old. However, because they are slow movers without much energy to spare roaming around, finding a mate can be difficult.

Female three-fingered sloths will emit high-pitched vocalizations to attract the attention of males.

Two-fingered sloths do not vocalize. Instead, both males and females mark their scent by rubbing their anal glands against tree branches to send messages about their reproductive status.

Males will fight over access to the female. Sloths try to knock their opponent out of the tree by biting, swiping their claws, and holding on to each other.

The victor will then move on through the canopy to the female. He will stay with the female and mate frequently for several days, defending her against any other males who try to approach.

Female sloths are promiscuous and will mate with many males while in heat. Unlike almost everything else sloths do, the act of mating is quick and typically lasts less than a minute.

male sloths fighting

7.2 Pregnancy and Birth 

A female sloth will have 1 baby approximately every 2 years. Two-fingered sloths will spend a full 12 months raising her baby. The period of maternal care is shorter for three-fingered sloths, averaging approximately 5 – 6 months.

sloth birth

Sloths give birth to a single baby at a time. A two-fingered female sloth will give birth to a single baby after a gestation of 11.5 months, and it is thought that a three-fingered sloth is pregnant for approximately 6 months (although this is still unconfirmed by science).

Sloths have occasionally been known to give birth to twins, but there is only enough room on the female’s chest for one baby, so the weakest twin will be rejected. In cases where one sloth has been observed with two babies, this is usually the result of an older baby still hanging around after a female has given birth again.

When she is ready to give birth, the mother sloth will usually descend from high up in the canopy to a lower branch and give birth while hanging upside down.

This way if the newborn sloth falls to the ground it won’t fall very far, and the mother can climb down to retrieve her baby.

Male sloths are not involved in raising their young, so the female sloth will spend the next year of her life raising her baby alone.

baby sloth with mother

7.3 Baby Sloths

A baby sloth is born with their eyes open, their claws sharp, and their teeth fully formed. Most newborn sloths weigh between 300 to 500 grams (about 10 to 17 ounces), and three-fingered infants are usually smaller than two-fingered infants.

Immediately after birth the baby will instinctively crawl up toward the safety of its mother’s chest and cling to her fur. Once there, the baby will hold on for the next six months, nursing small amounts of milk throughout the day.

As early as one week old, baby sloths will begin sampling leaves from around their mother’s mouth in addition to drinking milk.

baby sloth with mother

7.4 Interspecies adoptions in sloths

Although it is quite rare, there has been an unusual report in Costa Rica of a three-fingered sloth mother that adopted a two-fingered baby.

interspecies adoption

7.5 Lifespan

Nobody knows how long a wild sloth can live.

It is almost impossible to determine the age of a wild sloth. For most animals, their age can be estimated based on the length or wear and tear of their claws or teeth, but sloths are hypsodonts – their teeth and nails grow continuously throughout their lives, and are continuously worn down.

The only way to accurately age a wild sloth is through telomeric analysis, and in-depth studies of this kind have not yet been done.

Captive two-fingered (Choloepus) sloths are known to reach 40-50 years old, however, sloths were not bred in captivity until 50 years ago and so there has been little chance for any individual to exceed this figure.

The oldest known two-fingered sloth, named Paula, was 50  years old and lived at a zoo in Germany, while the oldest known three-fingered sloth, Buttercup, reached 27 years old at the Sloth Sanctuary of Costa Rica.

In captivity, sloths often have elevated stress levels, an excessively sedentary lifestyle, and eat an unnatural diet high in fructose.

This is because zoos do not typically have access to the new-growth tropical leaves that are a sloth’s natural diet and instead feed sloths fruit and vegetables they are not well adapted to eating.

These factors likely contribute to ill health and early mortality, therefore it seems likely that wild sloths may live longer in the wild than they do in captivity.

No one has ever followed a wild sloth from birth until death, and so any estimations on wild sloth longevity are only guesses.

baby sloth eating vegetables