I initially came out to the AWCRC as a research assistant in April 2018, but after spending 5 months here, I decided to apply for a PhD at Durham University. I was always interested in understanding the effects of human-wildlife interactions on the behaviour and physiology on wildlife, and studying the effects of crop foraging on the behaviour and physiology on chacma baboons in Alldays seemed like a perfect opportunity! After experiencing a year long delay due to the Covid-19 pandemic, I have finally returned to Alldays to start collecting data for my PhD.
While previous research has focused on improving methods for keeping wildlife out of fields, my project seeks to understand how access to crops affects the energetic condition and behaviour of baboons to better understand why primates crop forage. Crops represent a high value, energetically dense source of food. Around Alldays, crops tend to be available during the dry winter season when natural sources of food are scarce. Crop raiding, or crop foraging (the process by which baboons would acquire those energetically dense crops) by baboons should positively affect a baboon’s energetic condition, providing them with more energy than they could acquire from natural food sources during the dry season. However, crop foraging is risky. Crops are generally protected by farmers and field guards and baboons undertake a serious risk in being physically harmed or killed by farmers. The positive energetic effects of crops might be tempered by the physiological stress they endure while crop foraging.
My project plan is to compare two key metabolic hormones across two baboon groups, one with access to crops and one without, over the course of a year. The two hormones I will be monitoring at thyroid hormones (triiodothyronine, T3) and glucocorticoids (GCs, such as cortisol). These are two metabolic hormones with complementary roles. Thyroid hormones, such as T3, regulate basal metabolic rate and energetic consumption. For example, T3 levels decrease when animals experience a reduction in energy intake as a way to conserve energy. GCs, however, act to mobilise stored energy and are key in the energetic stress response. When animals face stressors, GC secretion mediates energy mobilization to provide the body with the energy required to cope with the stressor. Accordingly, GCs typically increase during food shortages and reductions in energy intake.
The complementary actions of T3 and GCs means that combining their measurements can allow us to assess the energetic challenges individuals face. Only a few studies have combined measurements of these two hormones, and none have done so to understand the context and the effects of crop foraging. Examining seasonal patterns of crop foraging behaviour of chacma baboons in Alldays with measurements of T3 and GCs in response to seasonal changes in food availability should clarify why baboons crop forage and the effect that the risks and rewards associated with crop foraging have on these animals.
In the rainy season when natural food is abundant, both crop foraging and non-crop foraging baboons should have higher T3 levels and lower GC levels. In the natural foraging baboons, T3 levels should be lower during the dry season when food is less available and GCs should be higher. The differences between the T3 and GC levels of the crop foraging and non-crop foraging groups at this time will give us a clearer idea of the effects of crop foraging and the risks and rewards of this behaviour. If the crop foraging baboons have higher T3 levels compared to their natural foraging counterparts during the dry season when they are engaging in crop foraging, this suggests the crop foraging baboons are consuming crops due in part to a lack of natural food sources and they are receiving energetic rewards from consuming crops. If the crop foraging baboons have lower GC levels compared to their natural foraging counterparts, this tells us they are primarily reaping the energetic rewards from consuming crops. However, if their GC levels are higher compared to the non-crop foraging group, this suggests they are coping with additional risks (or stressors) associated with crop foraging, such as being chased off by crop guards or shot at by farmers.
Quantifying T3 and GC levels between two groups of baboons with different access to crops during the dry season should help clarify how these animals respond to seasonal changes in natural and anthropogenic food sources and tease apart the effects of crop foraging and crop consumption on populations of baboons. This should explain when and why baboons crop forage, allowing for a more holistic understanding of the challenges in reducing crop losses to primates by allowing the baboon behaviour to be contextualised in terms of the risks and rewards.
Because I experienced a year-long delay due to the pandemic, my fieldwork is further behind that I thought it would be! We are still working on habituating our non-crop foraging group (which resides on Campfornis) and our crop foraging group (which is on a nearby farm). This is proving difficult for a number of reasons, but with the help of my wonderful research assistants I hope to have my groups habituated in a few months and we will be able to start doing daily follows to collect behavioural data and faecal samples.