How Weather Shapes Maned Sloths’ Behavior and Visibility
The Maned Sloth, also known as Bradypus torquatus, indigenous to the Atlantic coastal rainforest of Brazil, are threatened by human interference, hunting activities, deforestation, and habitat loss, as well as climate change that affect their behavior.
A study conducted by researchers from Universidade Estadual de Santa Cruz in Brazil, “Combined effect of ambient temperature and solar radiation on maned sloths’ behaviour and detectability,” investigated the effects of climate change and global warming on the Maned Sloth, particularly the combined effect of ambient temperature and solar radiation on Maned Sloths’ behavior and detectability.
The study aimed to analyze changing hourly temperatures throughout the day under two weather conditions (sunny and cloudy) and how they affect the Maned Sloths’ day-to-day activities, posture, and tree crown positions.
Temperature’s Role in Sloth Behavior
In general, animals subjected to extreme temperature fluctuations experience stress, which can result in conditions like hypothermia, hyperthermia, and harmful metabolic reactions.
Three-fingered sloths are known to have poor body temperature regulators and cannot generate heat to control their body temperature, thus relying on behavioral mechanisms. The following image shows the predictions of this study:
cloudy and rainy) in maned sloths’ activity levels (a, b), postures (c, d), and tree crown positions (e, f). Differences in slopes indicate that at a lower temperature, sloths should be more active, adopt more extended posture, and use more external parts of the tree crown during sunny rather than cloudy days, while the opposite should be true at higher temperatures. Crossed lines indicate that, at some point, these behaviours should be performed less frequently under sunny conditions to avoid overheating. Source: Combined effect of ambient temperature and solar radiation on maned sloths’ behaviour and detectability
Most mammals can maintain high and constant body temperature through shivering, sweating, panting, etc. However, due to the nature of the sloth, these mechanisms are energy-demanding and hard to perform when energy intake is low. These limitations are a result of their low-calorie diet, low metabolic rate, and low muscle mass percentage because of their arboreal and folivore habits. Three-fingered sloths’ body temperature fluctuates with the immediate temperature of their surroundings and are sensitive to the effects of temperature fluctuations and sun conditions.
The research
The site where the study took place was in Sapiranga Reserve in Mata de São João, Bahia, Brazil. The local government oversees the reserve, which receives a lot of tourists and faces urban expansion problems.
The landscape consists of a secondary forest fragment located on the Brazilian coastal sandbank. In the study area, the Maned Sloths usually feed on tree species with dense canopies and evergreen foliage.
In March 2020, eight Maned Sloths were tagged and equipped with small radio, harness-like backpacks.
The data were analyzed to determine how temperature and sunlight affect sloths’ behavior and visibility. For the data from the scan sampling method, the analysis involved:
• Examining extreme categories of sloth behavior, posture, and position: huddled or extended postures and inner/outer crown positions.
• Calculating the average temperature and the frequency of sloths exhibiting these behaviors during each hour.
• Developing computer models to assess how temperature and sun conditions affected behavior, posture, and position.
• Investigating the influence of individual sloths on the results.
• Evaluating whether the sloths’ posture and position made them more or less visible from the ground.
Key results
Most of the time, the sloths rest during the day (between 07:00 am and 05:00 pm) in an extended posture and in the outer part of trees. Surprisingly, when it was sunny, they became less active as it got hotter, which was an unexpected result for the species. However, when it was cloudy, they became more active as it got hotter.
Their posture, whether in a huddled or extended posture, changed with temperature and sunlight. They huddled more when it was cooler, especially on cloudy days, to keep warm.
When it was warmer, they stretched out in an extended posture more, especially in the sun, likely to gain extra heat. Their position in the tree crown, whether they were inside or outside the tree, was influenced by temperature. They tended to stay inside more when it was very hot (above 29–30°C) to avoid overheating.
Interestingly, their behavior and position in the tree didn’t seem to affect how easily they could be seen by humans. However, their choice to stay in the inner part of the tree when it’s hot could make them more vulnerable to capture.
Maned sloths and climate change
The findings suggest that as the climate gets warmer and drier in their habitat, sloths might face challenges in controlling their body temperature and behavior. This could be an additional threat to an already vulnerable species due to habitat loss and other human activities. Understanding these changes can help us predict how climate change might affect sloths in the future.
References
Lopes, G.S., Cassano, C.R., Mureb, L.S., Miranda, F.R., Cruz-Neto, A.P. & Giné, G.A.F. (2023) Combined effect of ambient temperature and solar radiation on maned sloths’ behaviour and detectability. Austral Ecology,00, 1–17. Available from: https://doi.org/10.1111/aec.13377
Darlene Buibas
-SloCo Collaborator
