Discussion

Thoughts About the Results

Individual: When looking at all the data, Thrax and Sophia were the only lemurs that appeared to have a strong preference for using their left hand. Humans are mostly right-handed, so it could make sense that lemurs would also be this way, but there's previous research on lemurs where left-hand use was actually more common than right-hand use. However, the statistical analyses I conducted found that focal individual was only a significant predictor of hand use for eating-related behaviors, and only in mongoose and ring-tailed lemurs. I wonder if the reason why the data were not significant for resting and locomotion-relating behaviors is because I didn't collect as much data for them as I was able to get for eating-related behaviors.

Biological Sex: When doing descriptive statistics, it appeared that left-hand use was slightly more common in males than females. This is similar to what previous research shows; However, the statistical tests I conducted showed that biological sex was not actually a significant predictor of handedness. This could be due to me having a small sample size (maybe if I had collected more data, then the statistical tests would have had smaller p-values), or it could be due to something else. Maybe lemurs have fewer differences between sexes than other species.

Species: When looking at the data using descriptive statistics, it appeared that the sifakas used their left hands a lot more than the ring-tailed and mongoose lemurs. This is similar to what I expected based on past readings. However, when I did the statistical analyses, it turns out that species is only a significant predictor of hand preference for resting-related behaviors. I wonder if this is because eating and locomotion-related behaviors are more related to where the food is or where the lemur needs to go, while grasps related to resting are based more on preference.

Limitations and Future Directions: What Would I Have Done Differently?

If I were to continue this research, I would want to collect a lot more data. This study took place over a 10-week internship, so my opportunities to collect data were limited. Many of the focal lemurs were resting a lot or did not forage much, so the available data from some individuals were scant. I also tried to collect data on foot use as well as data on behaviors such as grooming and landing, but I wasn't able to collect enough to do a thorough analysis. I would also want to include more lemurs to have a larger sample size. I did not have a large enough sample size to observe, for instance, if 10% of sifakas exhibit a left-hand preference.

Most previous research on limb preferences in non-humans uses manipulation. My study design instead uses observations of natural behaviors. This can provide many benefits because I am not requiring animals to move in unnatural positions or accidentally making them use a certain limb. However, there are also many challenges. When a lemur grabs a branch, for instance, I don’t know whether it was because it was their "preferred" side, or if it was because the branch just happened to be closer. Also, if a lemur was grasping a branch with one hand and eating with the other, I don’t know whether the eating hand was their "preferred" hand or it was the one grasping the branch. Behavior is dynamic and can be difficult to measure!

Another potential issue is that an animal also could have had pain or limited mobility on one side of the body, causing them to mostly reach with their non-preferred hand. None of the lemurs in my study were reported to have any pain or mobility problems, but it could still be possible.

A major limitation of my study was that not all of the focal subjects were in free-ranging enclosures. Only 2 free-ranging mongoose lemurs were available, so I had no choice but to observe 2 that were in indoor enclosures. Thrax and Gisela were in free-ranging enclosures at the beginning of the study but were later moved indoors before I was able to observe them.