Predator Foraging Strategies

Abstract

Foraging is a central component of an animal’s behaviour, essential for gathering energy to survive and to find mates for reproduction. Because resources aren’t always easy to find, and foraging can be costly, animals have been shown to employ strategies that increase success and efficiency in the task. These strategies also extend to those used by predators foraging for potential prey. In the case of predators, the act of foraging represents a significant challenge, because the food of a predator is mobile and responsive – both in the short-term (escaping) and the long-term (evolving). Prey anti-predator responses can range from dynamic individual behaviours to complex collective actions. Under selection to become better hunters, predators are likely to have evolved strategies to compensate and respond to these prey behaviours. This paradigm of reciprocal responses sets in place an evolutionary arms race between predators and prey, where the behaviour of one feeds back on the other. Despite the importance of studying both predators and prey in these reciprocating interactions, studies to date have focused almost exclusively on the prey side of the equation, and how they respond to predation risk. A consequence of the heavily-biased focus on prey behaviour in response to predators is that we have little idea of the effects that prey responses have on predator behaviour. A key reason for this is that predators are difficult to study. However, there is much to gain from doing so, with important implications for the ecology of both predators and prey. Primarily, we don’t have a clear picture of the feedback between predator behaviour and the anti-predator responses of prey. Secondarily, we don’t know what implications such feedback might have for predator-prey interactions. In my thesis, I wanted to take a predator’s perspective, and study several aspects of predator foraging strategies in order to better describe their form, understand their function, and consider how these strategies might have evolved. In Chapter 1, I studied the predation strategies of predators that hunt in groups. I built a framework that decomposed social predator foraging strategies into five fundamental dimensions of behaviour. By scoring the available literature using this framework, I ascribed each case study a multidimensional score, which I used to analyse the general relationships between the different dimensions across species. I then employed a method that used the multidimensional scores to place all species in context of one another, forming a behavioural landscape of social predation behavioural types. Analysing this multidimensional behavioural landscape illustrates how species from different taxa can use strategies with similar behavioural combinations, whilst hinting to the possible evolutionary pathways towards complex social predation strategies, and the fundamental behavioural features that underpin them. In Chapter 2, I looked more specifically at one aspect of the hunting behaviour of birds of prey, describing how these kinds of predators use temporal hunting strategies. I developed a method that extracted the probability of observing a given species of bird at different times of the day from two large citizen-science bird observation data sets. From these data, I could then infer the activity profiles of three raptor genera from two different continents. I found that species of the same genus use the same temporal hunting strategies, and for raptors that hunt songbirds, this temporal strategy is strongly linked to the temporal behaviour of the temporal activity provide I generated for their prey species. This result suggests a potential case of convergent co- evolution between predator and prey foraging strategies across two continents. i In Chapter 3, I built upon the insights into predator temporal foraging strategies by seeking to establish the relationship between hunting effort and hunting success rate. To achieve this, I used data which I collected from replicated nests of peregrines falcons (Falco peregrinus) which were fitted with webcams. From the video stream, I could record when adult birds left the nest and when they provisioned their young. Thus, I was able to quantify hunting effort using time away from nest, and variation in hunting success rate across time based on when prey items were brought back to the nest. I found that hunting effort is not evenly distributed, and does not appear to be strongly correlated with success rate. There was also a large amount of variation between nests, with different relationships between hunting effort and success rate, despite a similar bimodal pattern of prey captures and hunting success. These findings suggest that peregrines do not always incorporate the ‘catchability’ of prey into their temporal hunting strategies. It also indicates that peregrines might be using different hunting strategies to achieve the same result. This pattern could also be driven by other factors related to the individual, local prey, or meeting the energetic needs of young. These three chapters go some way to understanding different aspects of a predators hunting strategies, from exploring the landscape of strategies that social predators use, to describing how individual predators use temporal hunting strategies, and how these strategies might integrate information on prey behaviour.