Cathemerality is a unique and flexible activity pattern found mostly in lemurs. Cathemeral lemurs exhibit relatively evenly distributed activity across the 24-hour period. Although some species of lemur are broadly recognized as being cathemeral, other species have activity patterns that are still undetermined. The activity patterns of animals are largely influenced by environmental cues such as temperature, humidity, rainfall, and lunar illumination. However, the ways that animals respond to these cues are dependent on their own morphology and adaptations to a particular niche. This study examined the activity patterns of three species (Eulemur mongoz, Lemur catta, and Varecia rubra) of semi-free ranging lemurs living in the same 4-acre forest enclosure at the Lemur Conservation Foundation in Myakka City, Florida. Cross-species studies on captive and semi-free ranging populations can control for environmental variables and allow for inferences to be made about the driving forces of these activity patterns. I predicted that there would be a positive correlation between lunar illumination and activity patterns for all three species, and that there would be an inverse relationship between activity and meteorological factors such as temperature, humidity, and rainfall. I also predicted that overall, E. mongoz would exhibit the most evenly distributed activity pattern compared to the other two species, even in the absence of environmental differences experienced between species. Two individuals from each of the three species were fitted with accelerometers and activity was recorded in one-minute intervals for 45 days. Hourly temperature, hourly humidity, daily rainfall, and nightly illumination were also recorded. Behavioral observations were recorded and defined as "active" or "inactive" but were found to not accurately predict accelerometer outputs. The mean daily activity divided by the mean nightly activity was obtained for each individual and used in GLMM, ANOVA, and ANCOVA analyses. Daily mean activity and nightly mean activity were also used for some analyses. Results suggest that daily temperature, rainfall, and humidity have little influence on semi-free ranging lemur activity. However, day length and the nocturnal illuminance index (NII) were a significant influence in some cases. Overall, mongoose lemurs were found to exhibit a more cathemeral activity pattern than ring-tailed lemurs and were found to exhibit more nocturnal activity than diurnal activity during the month of July. An understanding of the behavioral flexibility of lemurs and the evolutionary context of cathemeral behavior would allow us to make inferences about the impending impacts of climate change and other anthropogenic disturbances and provide us with insight on how we could mitigate or minimize these impacts on endangered lemur species. This knowledge also helps us to make informed decisions about relocations, breeding programs, animal welfare, and the release of a previously captive animal. Primates provide many ecosystem services to humans and are important members of their ecological communities. However, they face many threats and populations worldwide are continuing to decline despite current conservation efforts.