Two-Toed Sloths: An Evolution of Care

Sloths' history in the United States stretches back further than most people might think. Giant ground sloths, growing over 10 feet long, lived in North America thousands of years ago, including the eastern United States. Nowadays, their much smaller descendants, two-toed sloths, roam Central America and northern South America—as well as the National Aquarium's Upland Tropical Rain Forest.

Sloths have a long history at the Aquarium, as they were one of the original species housed in the building in 1981. The first sloth, a Hoffmann's two-toed sloth nicknamed Rapunzel, lived at the Aquarium from 1981 to 2007. In 2007, the Aquarium welcomed our first Linne's two-toed sloths. Over the years, six sloth babies have been born at the Aquarium—including Xeno in 2010, who was hand-reared by staff after his mother passed. Today, three female Linne's two-toed sloths (nicknamed Scout, Piper and Buttercup) live in our rain forest exhibit.

Over the past 43 years, our understanding of sloth biology has evolved and now informs their care at the Aquarium. Sloths are unique and require a specialized habitat and care, necessitating thoughtful planning and consideration every step of the way.

Not Your Average Mammal

Sloths are not your average treetop dwellers. Unlike most arboreal animals, sloths spend much of their lives hanging upside down from all four limbs. The seven sloth species belong to two families—three-toed and two-toed sloths—named for the number of toes on their forefeet. Three-toed sloths are often represented in pop culture as slow with a sedentary lifestyle, giving all sloths a reputation as lazy. However, two-toed sloths are active animals, moving every day and even fighting with other animals.

A Range of Temperatures

Unlike most mammals, sloths' body temperatures are affected by their environment, requiring a habitat with spaces to warm up and cool down. The guest path in Upland Tropical Rain Forest stays around 82 degrees Fahrenheit, but the rest of the rain forest—which the sloths can access—can be as cool as 75 degrees Fahrenheit. For example, the exhibit is warmer and brighter at its highest points due to heat rising and the sun shining through the glass. Farther down, the dense vegetation provides shade from the sun and less heat. The sloths have ample access to the varying temperatures in the exhibit, allowing them to thermoregulate.

"Our approach to animal care is deeply rooted in providing habitats that support and solicit natural behaviors," Assistant Curator Deb Dial said. "I love watching the animals use the space."

Designing a Two-Toed Sloth Habitat

Two-toed sloths are quite active at night and need a variety of climbing spaces in their habitat to explore. At the Aquarium, our team designed the Upland Tropical Rain Forest to cleverly meet the needs of free-roaming sloths.

For example, the mesh around the exhibit acts as both a barrier and a climbing structure. The gaps in the taut mesh are big enough to let sloths grab on to move around the exhibit. Designers also provided hiding spaces; trees with long, sturdy limbs; branches that touch the ground; and plants that provide cover and shade for the sloths and other animals in the exhibit. When the sloths need rest, they spend time in the large ficus tree growing above the upper deck or in other spaces less visible to guests.

Over the years, Animal Care staff have published work about our observations of sloths' diets, habitat needs, social dynamics, hand-rearing guidelines and more to share our knowledge with other organizations caring for sloths.

"My favorite thing to say about sloths is the more you learn about them, the less you understand," Deb said. "Their behavior is linked to their environment, physiology and individual experience, so their care and wellbeing are based on understanding all those pieces."

Lessons Learned: Hand-Rearing Xeno

In 2010, our team learned that in addition to a specialized habitat, we need adaptable staff. Xeno, a two-toed Linne's sloth named after sloths' scientific name Xenarthra, was born at the Aquarium. Unfortunately, Xeno was orphaned at about six weeks old, so we started our hand-rearing care program. For sloths, this hand-rearing includes bottle-feeding goats' milk, using stuffed animals and other strategies to help them survive without their mothers.

Baby sloths are born with their eyes open, a full coat of fur and soft nails. After birth, the baby climbs onto its mother's stomach, where it stays for the next couple of months. After a few weeks, the baby explores more of its environment while keeping its back limbs attached to its mother before finally separating after about one year. Baby sloths require a lot of contact and carrying, especially during their first four to five months, necessitating an intensive care plan.

Around-the-Clock Care

To meet Xeno's needs, staff cared for him 24/7, feeding and carrying him to ensure his wellbeing. The team used stuffed animals as surrogate mothers and a baby sling to carry Xeno around. For months, staff carried Xeno, attached to a surrogate mother, around the back offices and sat with him at their desks.

Xeno never developed a strong nursing response, and staff soon learned that he was interested in eating solid foods after Ken Howell, curator of Australia: Wild Extremes and Upland Tropical Rain Forest, noticed the baby sloth reaching for a plant on his desk. Staff slowly began feeding Xeno solid food like steamed green beans, yellow squash, zucchini and sweet potato, which augmented the nutrition from the goat's milk he received.

After about 10 months, Xeno moved into a habitat in the back of the Upland Tropical Rain Forest. Staff carefully monitored Xeno's progress and cable-tied a surrogate mother to tree branches for him to sit on. About one year after his birth, Xeno separated from his surrogate mother, moved into a sleeping basket and soon joined the main exhibit before moving to another institution some years later.

Sloth Species Survival Plan

Sloths are unique animals that require specialized care, different from other mammals. Through habitat design, understanding misconceptions about sloths and a hand-reared baby sloth, the Aquarium's animal care team continues to enhance its sloth expertise.

Outside of the Aquarium, sloths throughout Central America and northern South America are often hit by cars as they're trying to cross roadways, electrocuted on powerlines or threatened by habitat loss due to deforestation. The Aquarium participates in the sloth Species Survival Plan (SSP) program through the Association of Zoos and Aquariums (AZA), which tracks and maintains genetic diversity to ensure sustainability. The Aquarium has participated in the sloth SSP program for over 15 years, as well as other SSPs.