No abstract

For herbivores, vigilance usually involves a trade-off with foraging, and a further trade-off between antipredator and social vigilance. Thus individual variation in vigilance may result in significant fitness consequences. We used mixed-effects models to document individual variation in vigilance in wild adult female eastern grey kangaroos (Macropus giganteus) in Queensland, Australia. We tested the effects of group size, presence of adult males and wind on vigilance patterns and variation by analysing 399 five-minute samples on 31 individually identified females who were foraging on the periphery of groups. We determined the proportion of time that individuals spent vigilant, and the proportions of vigilance time spent in social versus antipredator vigilance and in low- versus high-intensity vigilance postures. The proportion of time females spent vigilant decreased with increasing group size but was not affected by wind speed or male presence, while the amount of their vigilance time spent in social vigilance was affected by interactions among the variables. After controlling for these effects, 13 females’ vigilance patterns were significantly different from the population mean. Individual variation was also found in vigilance postures used and the effect of male presence. Understanding individual variation in vigilance is important for understanding individuals’ antipredator and social strategies.

Prey individuals must constantly make decisions regarding safety and resource acquisition to ensure that they acquire enough resources without being predated upon.These decisions result in a trade-off between resource acquisition behaviours (such as foraging and drinking) and safety behaviours (such as grouping and vigilance). This tradeoff is likely to be affected by the social and environmental factors that an individual experiences, including the individual's location in the landscape. The overall objective of my PhD was to understand the decisions a migratory ungulate makes in order to acquire enough resources, while not becoming prey, and to understand how these decisions are influenced by social and environmental factors. In order to do this, I studied the behaviour of blue wildebeest (Connochaetes taurinus) in Etosha National Park, Namibia, between 2013 and 2015. I studied wildebeests' behaviour while they acquired food and water and moved within the landscape. Along with observational studies, I also used lion (Panthera leo) roar playbacks to experimentally manipulate perceived predator presence to test wildebeests' responses to immediate predation risk.For Chapter 2 I studied the foraging-vigilance trade-off of wildebeest to determine how social and environmental factors, including the location within the landscape, were correlated with wildebeests' time spent foraging and vigilant as well as their bite rate. I found that environmental variables were more important than social variables in predicting the foraging-vigilance trade-off of adult wildebeest. Food availability was the most important factor, with wildebeest increasing time spent foraging, at a cost to vigilance time, when food was more readily available. This result suggests that wildebeests' behavioural decisions were more affected by forage availability than predation risk.The objective of Chapter 3 was to study the effects of individual characteristics, social variables and environmental variables on wildebeests' behaviour during their approach to, time at, and retreat from, waterholes, to understand the water acquisition-safety tradeoff. I looked at time spent vigilant, moving and drinking as well as step rate. and forage competition factors. Wildebeests' within-group density was associated with forage competition more than the landscape of fear. These findings suggest that wildebeests' landscape-use and within-group density were altered in response to predator avoidance and resource acquisition.My thesis provides insights into how prey species trade-off between resource acquisition and safety. By assessing the social, environmental and landscape variables that affect the trade-off, this study showed that prey adapt their behaviour according to group dynamics, forage availability and predation risk and suggests that individuals may consider different aspects of their environmental and social surroundings when accessing different resources. Therefore, future studies should examine social, environmental and landscape variables togeth...