Influence of manipulated risk of predation in a predator–prey foraging game in a patchy environment: Egret and goldfish in experimental aviaries

Background: Predator and prey engage in a behavioural game in which the behavioural decision of one affects that of the other. Behavioural games can be influenced by differential predation risk caused by habitat patchiness in the environment. Patches may provide prey with a differential risk of predation due to the size of area that provides refuge. The predator has to respond to the existence of patches with varying degrees of predation risk because this variable affects the time they spend foraging in each patch. Question: Will the predator and the prey respond optimally to each other in a behavioural game? Methods: We conducted behavioural experiments in two identical aviaries (7 m diameter), each with three separate pools (1.52 m diameter, 0.60 m deep, ∼1000 litres capacity). Each pool had two habitats, one a horizontal cover in the centre of the pool (the refuge), the other open water (the risky patch). We used little egrets (one per experiment) and goldfish (15 fish per pool) as predator and prey respectively. We used small, medium, and large cover sizes as refuge, thus manipulating the predator’s killing efficiency. We assigned a refuge size to each pool at random. We then observed the behavioural games of both players for 6 hours per experimental day. We recorded the time fish spent in the refuge; the time fish took to return to open water after being frightened into seeking cover (refractory time); the amount of food consumed by the fish; the time the egret spent in a single pool; the time it took the egret to return to that pool after leaving it; the number of fish caught by an egret during each phase of the experiment; and whether a fish was caught while it swam in open water or hid under a refuge, Results: Contrary to our prediction, the fish were more active in the pools with smaller covers even though that is where they suffered the highest mortality. The egrets did not differentiate between cover sizes, spending a similar amount of time foraging at all three pools. However, the egrets timed their visits to the pools with the three sizes of covers in a way that matched the fish refractory times in those pools. The egrets returned to a pool just when the fish were beginning to re-emerge from under the cover, thus maximizing their capture success.