Factors influencing the use of searching images by blue jays hunting for cryptic prey.

摘要

Insect-eating birds can use searching images to detect cryptic prey. That is, they can learn what the prey looks like, and attend to certain visual features of the prey in order to more easily find additional items of the same type. Much of the research in this area has focused on explaining the mechanisms that facilitate prey recognition. Recently, however, researchers have begun to demonstrate that predators utilizing searching images can favor the evolution of polymorphisms in prey populations. To better understand how predators and prey interact, it is important to understand the variables that influence the effectiveness of searching images. In the following chapters, research investigating several factors is presented. The importance of the degree of resemblance in appearance of two prey types is discussed in Chapter 2. In Chapter 3, the effect of the elapsed time between encounters of the same prey type is discussed. Finally, the effects of prey symmetry are discussed in Chapter 4. Three main conclusions can be drawn from these studies. First, prey types that are very similar in appearance may fall into the same searching image, and they may suffer equal predation rates as a consequence. Second, searching image effects in blue jays can be long-lasting. Third, while crypticity of prey has great influence on searching image effects, effective camouflage may be achieved regardless of pattern symmetry.; The results suggest that prey need to evolve relatively large differences in color pattern to escape a predator's search image. The results also show that blue jays retain searching images for longer durations than pigeons, perhaps as a result of the differences in the distribution of the foods that the two groups of birds search for. Finally, symmetry of prey seems to be less useful for blue jays than predicted, although it remains unclear whether there are large differences in the ways that humans and birds perceive symmetry. In addition, while highly effective background matching seems possible regardless of symmetry, small differences in prey crypsis may have important consequences.