Visually hunting predators must overcome the challenges that prey groups present. One such challenge is the confusion effect where an overburdened visual system means predators are unable to successfully target prey. A strategy to overcome confusion is the targeting of distinct, or odd, individuals (the oddity effect). In live prey experiments, manipulation of group member phenotypes can be challenging and prey may differ on more than the single feature one intends to define as odd. The use of highly controllable computerized stimuli to study predator–prey interactions is increasingly popular in the field of behavioral ecology. However, to our knowledge, the validity of computerized stimuli to study the oddity effect has not been established. Predator choice experiments were conducted using naive stickleback predators to ascertain whether the oddity effect could be demonstrated in the absence of live prey. We found evidence for both the oddity effect and preferential targeting of group edges and low-density regions, as would be predicted if predators targeted prey individuals to minimize confusion. The oddity effect was evident at a low threshold, above which dots were no longer perceived as odd and no longer attacked more often than expected by chance. We conclude that computerized stimuli are an improved, practical method for studying oddity effects while further validating the use of similar methods for studying other aspects of visual predation. In addition to higher control of “prey” appearance, the replacement of live prey animals with digital stimuli is ethically beneficial and reusing code improves experimental efficiency.

Animals can adapt to changes in their environment through behavioural or developmental plasticity, but studies of these responses tend to focus on either short-term exposure of adults to the changed conditions, or long-term exposure of juveniles. Juvenile guppies Poecilia reticulata reared in low-light environments have previously been shown to make a sensory switch to using olfactory, rather than visual, cues in foraging. It is not clear whether this compensatory sensory plasticity is limited to juveniles, or whether longer term exposure allows adults to similarly adapt. We investigated how adult guppies that were exposed to light or dark environments for 2 and 4 weeks responded to visual, olfactory and a combination of both food cues, in both darkand light-test environments. We found that after 2 weeks of exposure, adult guppies were better able to locate a food cue in light test environments regardless of their exposure environment. After 4 weeks, however, guppies were more successful at locating the food cue in the environment they had been exposed to, suggesting that dark-exposed guppies adapted their behaviour in response to their environment. We found that foraging was most successful when both visual and olfactory cues were available and least successful in the presence of olfactory cues, suggesting that the mechanism behind the change in success for darkexposed guppies was not due to increased reliance on, or sensory switch to olfactory cues. Significance statement Human-induced environmental change often acts to disrupt an animal's sensory environment. For example, turbidity can degrade the visual environment, resulting in reduced foraging rates in fish. Juvenile guppies (Poecilia reticulata) can compensate for the reduced visual information available in low-light environments through developmental changes that allow them to rely on an alternative sense, olfaction. This ability, however, may be limited to a critical developmental window, or possible throughout life. Here, we show that while adult guppies are generally better able to locate food resources in well-lit environments, after four (but not two) weeks living under low-light conditions, fish were better able to find food in dark environments than in the light. However, unlike juvenile fish, they did not seem to be relying more on olfactory cues to do so.