Male Sloth Speculum (colorful fur patch on back)

Sloths have evolved many mysterious behaviours that we are constantly trying to understand; for example, why are they so slow? Why do they come down to the ground to defecate? What is their sleep cycle?

The fact that male Three-fingered sloths have evolved bright orange patches of fur on their backs (speculum) seems to have been overlooked. Considering a sloths survival strategy is camouflage, there must be a good reason for this patch to develop.

Why has this speculum evolved and how does it benefit the sloth? Why don’t females have them? Why does speculum size and colour differ so much among individuals? This begs so many questions that we are hoping to answer here at the Sloth Sanctuary.

Biologist Becky Cliffe has begun a project investigating the male sloth speculum. She believes that this patch of hair is a testosterone-dependent signal of quality,  i.e., the bigger and stronger the sloth, the bigger and brighter the speculum appears. We are taking measurements of body size, weight, and patch size, pattern and colour intensity of all of the male sloths in the surrounding forest. Slowly we are building a speculum library that will help us draw scientific conclusions about the speculum.