Life in town does not turn a sloth into a hurried city animal. New tracking data suggests something subtler: sloths living around Puerto Viejo in Costa Rica divide their time between sleep, rest and activity a little differently from sloths in primary rainforest.
The findings come from a September 2026 update from the Urban Sloth Project. They are preliminary, which means researchers are sharing patterns from an ongoing study rather than presenting a final explanation. That caution matters. The data shows that habitat and behaviour are linked, but it does not yet tell us exactly why.
How do you tell whether a sloth is asleep?
Watching from the ground is not enough. A motionless sloth might be asleep, quietly resting or simply hidden by leaves. Researchers therefore use VHF and GPS collars fitted with accelerometers, along with small data loggers that record movement, position and temperature many times each second.
The project's latest comparison includes 49 sloths. Thirty-eight lived in urban sites around Puerto Viejo and 11 lived in primary forest. Both local species were represented: 28 brown-throated three-fingered sloths and 21 Hoffmann's two-fingered sloths.
Together, the devices collected 31,819 hours of behavioural data. That is more than three and a half years of continuous monitoring spread across individual animals. It allows the team to examine a full day in far more detail than occasional sightings could provide.
Sleep and rest are not the same thing
For the analysis, each 24-hour period was divided into sleep, rest and active behaviour. The distinction between sleep and rest is easy to miss. A resting sloth may remain completely still while awake and responsive. A sleeping sloth is genuinely asleep and less responsive to what is happening nearby.
Among three-fingered sloths, the urban group slept for an average of 32.8% of the day, compared with 24.4% in primary forest. They rested for 54.6%, compared with 62.8% in the forest. Active time was almost identical: 12.6% in town and 12.8% in primary forest.
That does not mean urban three-fingered sloths were simply more inactive. Their total active time barely changed. Instead, some of the time classified as quiet rest in the forest group appeared as sleep in the urban group.
The difference was smaller for two-fingered sloths. Urban animals slept for 37.8% of the day, compared with 34.1% in primary forest. They were active for 16.2%, compared with 17.4% in the forest. Across both species, males were generally less active than females regardless of habitat.
Temperature around the sloth may matter
The data loggers also let researchers compare behaviour with air temperature, the temperature beside the animal, sunlight and wind. The early patterns are complicated, which is exactly what makes them interesting.
Higher general air temperature tended to be associated with more activity in both species. Yet higher microhabitat temperature, measured directly beside the sloth, tended to be associated with less activity. That relationship was strongest in urban sites.
Sunlight and wind did not produce one simple rule either. Their associations varied by species and habitat. The project is not yet claiming a cause. A warmer spot beside a sloth might differ in shade, canopy structure or other ways that still need to be mapped and tested.
This fits the wider purpose of the Urban Sloth Project: understanding how rainforest disturbance changes the choices available to wild sloths. A town is not just a forest with houses added. It can alter shade, wind, heat, tree connections and the safe routes an animal can use.
Two species, two daily rhythms
The latest data also reinforces an important point: there is no single timetable followed by every sloth. Three-fingered sloths in the study were active during both day and night, a pattern called cathemerality. Their activity was greater at night overall, but it was not restricted to darkness.
Two-fingered sloths remained mostly nocturnal, with activity concentrated at night. Some urban individuals showed slightly more daytime activity than their primary-forest counterparts, but individual variation remains important.
Earlier activity research on wild sloths found that neighbouring animals could follow surprisingly different schedules and that movement often occurred in short bursts separated by longer quiet periods. The new urban comparison adds habitat to that individual picture without turning it into a tidy universal rule.
Why preliminary results still matter
The researchers are careful not to say that urban sloths have adapted successfully, or that more sleep proves they are comfortable. A behavioural difference can be measured before its cause or welfare meaning is understood.
The next phase will combine the movement records with fine-scale drone mapping of canopy cover, tree connectivity and microclimate. That could help reveal which features of a landscape sit behind the differences, rather than merely showing that town and forest sloths behave differently.
There is already a practical lesson. Good conservation decisions need to reflect the world a sloth experiences at branch level. Protecting connected trees, cool refuges and safe canopy routes may matter in ways that cannot be seen from a road or a satellite image alone.
For now, the honest answer is also the most exciting one: urban sloths sleep differently, and scientists are still working out why. Every additional hour of careful monitoring brings that answer closer while keeping the animals' real, varied lives at the centre of the story.
Sources and further reading
- The Sloth Conservation Foundation: Sloths in Town, preliminary Urban Sloth Project findings
- The Sloth Conservation Foundation: The Urban Sloth Project
- The Sloth Conservation Foundation: behaviour and activity budgets of sloths
Featured image: The Sloth Conservation Foundation, showing Deborah and her baby Mel using a canopy bridge.