Ecology and Neurophysiology of Sleep in Wild Sloths

Abstract

Although every animal carefully studied has been found to sleep, the actual function of sleep remains an unanswered question among scientists. One approach is to examine the diversity of sleep seen among animals by studying sleep in various species sleeping under different environmental conditions. This comparative approach may help identify traits that correlate with sleep amounts, which may provide clues to sleep’s purpose. However, until this dissertation, all comparative work has been done on captive animals, and thereby provides limited insight into how animals sleep naturally. Throughout this dissertation, we examine sleep in three species of wild sloths inhabiting the rainforests of Panama. We start in Chapter 1 by establishing a working method for recording EEG’s in wild three-toed sloths. Surprisingly, we found that wild sloths slept 6 hours less than captive sloths, suggesting that captivity may strongly influence an animals sleep amount. In Chapter 2 we examine the effect of predation pressure on sleep by comparing sleep in two species of three-toed sloths with different natural predation risks. We find that sloths at high risk for nocturnal predation are less likely to be active at night then the predation risk-free sloths. We also find interesting differences in the amount of REM sleep, as well as in the spectral densities of NREM sleep-related EEG activity. In Chapter 3, we record sleep for the first time in wild two-toed sloths, finding that they sleep on average 10.9 hours per day, far less than the 20 hours often cited in historical literature. We also compare the effectiveness of measuring sleep behaviorally with accelerometers, and find that estimating sleep without an EEG in an animal such as sloths can overestimate the time spent sleeping. In Chapter 4, a radio-collared three-toed sloth was predated by an owl, leading us to examine the behavioral and anatomical trade-offs that have contributed to a cryptic lifestyle. Overall, this dissertation presents novel findings from several interesting studies examining sleep and predation in wild sloths.