Searching image in blue jays: Facilitation and interference in sequential priming

Abstract

Repeated exposure to a single target type (sequential priming) during visual search for multiple cryptic targets commonly improves performance on subsequent presentations of that target. It appears to be an attentional phenomenon, a component of the searching image effect. It has been argued, however, that if searching image is an attentional process, sequential priming should also interfere with performance on subsequent nonprimed targets, and such interference has never been unequivocally demonstrated. In blue jays (Cyanocitta cristata) searching in an operant apparatus for targets derived from images of cryptic moths, detection performance was strongly facilitated in the course of a sequential prime but was relatively unaffected by sequences of mixed target types. Detection accuracy in subsequent probe trials was enhanced by priming with targets of the same type, whereas accuracy on cryptic probes following priming with a more conspicuous target was significantly degraded. The results support an attentional interpretation of searching image. 461Predators that search for cryptic prey items make use of a wide range of cognitive capabilities. They learn to discriminate the visual features of their prey from the background (Curio, 1976;Krebs, 1973;Lawrence, 1985), they adopt response strategies that maximize their rate of prey discovery (Endler, 1991;Gendron, 1986; Gendron & Staddon, 1983), and they undergo perceptual changes that temporarily increase their ability to detect more abundant prey types, a phenomenon termed hunting by searching image (Tinbergen, 1960). Tinbergen developed the concept of searching image to account for the fact that insectivorous birds select more abundant prey types disproportionately often, while effectively overlooking rarer ones (Allen, 1988;Bond, 1983; Bond & Kamil, 1998). Tinbergen noted that his birds tended to take prey items in sequential runs, suggesting that, at any given moment, they were searching for only one kind of prey (see, also, Bond, 1982;Dawkins, 1971). He hypothesized that if the birds were filtering out alternative stimuli and limiting their search to the visual features characteristic of a single prey type, this would increase their ability to detect that prey and reduce the detectability ofalternative prey types (Tinbergen, 1960). Over a long series of captures, such a bias could account for the observed population effects (Bond & Kamil, 1998).To reproduce the searching image phenomenon in the laboratory and make it accessible to experimental manipOur research was supported in part by NSF Grant IBN-962 1044. Correspondence concerning this article should be addressed to either A. B. Bond or A. C. Kamil, School of Biological Sciences, 348 Manter Hall, University of Nebraska, Lincoln, NE 68588-0118 (e-mail: abond@ unlserve.unl.edu or akamil@unlserve.unl.edu). Images of moths and cryptic backgrounds, as well as the computer algorithms used in image generation, are available on our Web site (httpt//niko.unl.edu/r-jaylab/virtprey.htm).ulation, Pietrewicz and Kamil ...

A generalized functional response for predators that switch between multiple prey species

“…One potential underlying mechanism is the trade-off resulting from the limited total attention a predator can give to prey (44)(45)(46), which leads to the formation of search images (30,35,(47)(48)(49)(50)(51)(52). To some degree, the effects of prey quality can implicitly be incorporated in our model by multiplicative factors contributing to the base attack rates and/or switching rates.…”

Visual predators select for crypticity and polymorphism in virtual prey

“…[23][24][25] To furnish our jays with a functional virtual ecology, we generated synthetic, digital moths-bilaterally symmetrical triangles about 6 mm high-and displayed them to the birds overlaid on a complex, granular background ( Figure 1). 18,19 To avoid potential problems with avian color perception, the displays were constructed using a 64-level grey scale. 26 Each moth phenotype was constructed from specifications in a virtual chromosome, through an algorithm derived from salient features of the genetics of lepidopteran wing patterns.…”

“…In our previous study of virtual ecology, frequency-dependent selection produced stable dynamics among a set of three morphs, but the consequences of adding new morphs seemed to depend on how difficult they were to detect. 18 In one case, the new morph was similar in crypticity to those in the initial population, and a stable configuration of four prey types was produced. A second new morph, however, was so cryptic and distinctive that few of them were ever discovered.…”

“…14 Recent studies have confirmed the occurrence of searching image effects, demonstrating that the ability to detect cryptic prey increases when items of similar appearance are encountered in rapid succession and that a search for one cryptic prey type can actively interfere with the detection of alternative forms. [15][16][17][18] Because the dynamic interplay between predator behavior and prey appearance is difficult to evoke under controlled conditions, much of the earlier empirical support for frequencydependent selection of cryptic prey was fragmentary and indirect. 19 To circumvent this constraint, we developed a "virtual ecology", in which captive blue jays hunt for artificial, digital moths on computer displays.…”

“…Our previous work with this system has shown that predators searching for a set of fixed prey types do exhibit frequency-dependent selection, that such selection does serve to maintain stable prey polymorphism, and that the effect is almost certainly attributable to hunting by searching image. 18,19 Because frequency-dependent selection operates against common, familiar phenotypes, it should also lead to the proliferation of new, disparate phenotypes in an initially monomorphic prey population. 4,[20][21][22] This prediction has been subjected to only limited experimental testing.…”