Sunbathing in Primates: Experimental Evidence Discounting Vitamin D 3 Synthesis as a Primary Function in Ring‐Tailed Lemurs ( Lemur catta )

ABSTRACT Background The function of sunbathing is often assumed to be thermoregulation, but UV‐B wavelength light also allows subcutaneous synthesis of vitamin D 3 . We sought to determine the primary function of sunbathing in ring‐tailed lemurs. Methods We gave five lemurs at the Toronto Zoo choice of two sunbathing spots (one UV‐B and one UV‐A lamp, counter‐balanced for site preference) as their diet was increased in vitamin D 3 . We measured sunbathing bouts at each lamp using a video camera trap. Results Positional sunning behavior was more frequent in the darkest months, when it was colder, and during sunnier conditions. The lemurs had a strong site preference and basked more at the UV‐A lamp. Increasing dietary vitamin D 3 did not change their lamp and site preferences. Conclusion We found no supporting evidence that sunbathing in ring‐tailed lemurs primarily functions for vitamin D 3 synthesis, but we include methodological suggestions for others to revisit this hypothesis.