Pigeons (Columba livia) searched for hidden food in a rectangular environment constructed to eliminate external orientation cues. A feature group was initially trained with distinct features in each corner. A geometric group was initially trained with no featural information. Tests revealed that both groups encoded the geometry of the apparatus. The geometric group was then retrained with features, and a series of tests was administered to both groups. Transformation tests revealed that the groups differed in reliance on features versus geometry. Pigeons in the feature group followed the positive feature even when it was placed in a geometrically incorrect corner, whereas pigeons in the geometric group showed shared control by features and geometry. Both groups were able to use features in corners distant to the goal to orient themselves, and both groups relied more on the color than on the shape of the features. Survival within an environment frequently requires efficient processing of spatial information. Spatial abilities underlie activities that are critical for the individual (e.g., establishment of lodging, avoidance of predation, and attainment of nourishment) and for a species (e.g., migratory behavior or reproduction); these activities may involve a variety of mechanisms. Navigation, for example, may be achieved through inertial guidance, orientation to a beacon, piloting by use of landmarks, or developing a spatial representation of the environment (Gallistel, 1990). Questions concerning which aspects of an environment are encoded and used in navigation have been addressed in recent research (for reviews, see Cheng & Spetch, 1998; Gallistel, 1990; and Poucet, 1993). Many studies have shown that animals can encode and use multiple sources of information to locate a goal (e.g., Spetch & Edwards, 1988) and that the primacy of control by different sources of information may differ according to context (e.g., Strasser & Bingman, 1996) or species (e.g., Brodbeck, 1994). One particularly interesting set of results has emerged from studies that have controlled and manipulated the information available for encoding by restricting access to navigational cues in an enclosed environment and by disrupting other positional cues through disorientation techniques (Cheng,

Pigeons and humans searched for a goal that was hidden in varied locations within a search space. The goal location was fixed relative to an array of identical landmarks. Pigeons searched on the laboratory floor, and humans searched on a table top or an outdoor field. In Experiment 1, the goal was centered in a square array of 4 landmarks. When the spacing between landmarks was increased, humans searched in the middle of the expanded array, whereas pigeons searched in locations that preserved distance and direction to an individual landmark. In Experiment 2, the goal was centered between and a perpendicular distance away from 2 landmarks aligned in the left-fight dimension. When landmark spacing was increased, humans, but not pigeons, shifted their searching away from the landmarks along the perpendicular axis. These results parallel those obtained in touch-screen tasks. Thus, pigeons and humans differ in how they use landmark configuration. Many creatures remember places to return to by the use of visual landmarks. In this spatial search strategy, some kinds of spatial relationships between the goal and its surrounding landmarks are encoded and are later used to find the goal again (for reviews, see Collett, 1992; GaUistel, 1990). In many studies of landmark-based spatial memory, the landmarks defining the goal are shifted about from one trial to the next, thus forcing the subject to use the experimentally specified landmarks to locate the target. This method has demonstrated the use of landmarks in studies with insects (e.g.,

We report that adult nutcrackers (Nucifraga columbiana) and newborn domestic chicks (Gallus gallus) show a leftward bias when required to locate an object in a series of identical ones on the basis of its ordinal position. Birds were trained to peck at either the fourth or sixth element in a series of 16 identical and aligned positions. These were placed in front of the bird, sagittally with respect to its starting position. When, at test, the series was rotated by 90° lying frontoparallel to the bird's starting position, both species showed a bias for identifying selectively the correct position from the left but not from the right end. The similarity with the well-known phenomenon of the left-to-right spatially oriented number line in humans is considered.

The traditional ‘mark test’ has shown some large-brained species are capable of mirror self-recognition. During this test a mark is inconspicuously placed on an animal’s body where it can only be seen with the aid of a mirror. If the animal increases the number of actions directed to the mark region when presented with a mirror, the animal is presumed to have recognized the mirror image as its reflection. However, the pass/fail nature of the mark test presupposes self-recognition exists in entirety or not at all. We developed a novel mirror-recognition task, to supplement the mark test, which revealed gradation in the self-recognition of Clark’s nutcrackers, a large-brained corvid. To do so, nutcrackers cached food alone, observed by another nutcracker, or with a regular or blurry mirror. The nutcrackers suppressed caching with a regular mirror, a behavioural response to prevent cache theft by conspecifics, but did not suppress caching with a blurry mirror. Likewise, during the mark test, most nutcrackers made more self-directed actions to the mark with a blurry mirror than a regular mirror. Both results suggest self-recognition was more readily achieved with the blurry mirror and that self-recognition may be more broadly present among animals than currently thought.

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Clark's nutcrackers (Nucifraga columbiana), a non-social corvid, cache much of their food in order to survive periods of resource uncertainty. These caches are at risk as they are subject to pilferage from other animals including conspecifics. Potentially, nutcrackers can ensure the safety of these caches by keeping track of whether they have been observed making a cache and subsequently engage in cache protection strategies-strategies that have been shown by other members of the corvid family (e.g., scrub-jays and ravens). Behaviors including creating more caches, eating a higher proportion of seeds, and re-caching existing compromised sites have been shown in laboratory settings with social corvids and have provided preliminary evidence of the complex cognitive abilities of corvids. In the present study, Clark's nutcrackers are shown to engage in similar cache protection behaviors when observed by a conspecific. Furthermore, we show that these behaviors are a result of social, rather than associative, cues.

Four pigeons were trained in a successive same/different procedure involving the alternation of two stimuli per trial. Using a go/no-go procedure, two different or two identical color photographs were alternated, with a brief, dark, inter-stimulus interval, on a computer screen for 20 s. Pigeons learned to discriminate between same (S+) and different (D−) sequences with moderate to large contrasts between successive pictures. Analyses of pecking behavior within single trials revealed this discrimination emerged at the earliest possible point in the sequence (i.e. by the presentation of the second item). Pigeons transferred to novel color and gray-scale pictures, and showed savings in tests with novel video stimuli. These results suggest that same/different discrimination and concept formation can be acquired with successively presented pairs of stimuli by pigeons. When combined with results using simultaneous same/different presentations, these findings further support a qualitative similarity among birds and primates in their capacity to judge certain types of stimulus relations.

Adults searched for a goal in images of a rectangular environment. The goal's position was constant relative to featural and geometric cues, but the absolute position changed across trials. Participants easily learned to use the featural cues to find the target, but learning to use only geometric information was difficult. Transformation tests revealed that participants used the color and shape of distinct features to encode the goal's position. When the features at the correct and geometrically equivalent corners were removed, participants could use distant features to locate the goal. Accuracy remained above chance when a single distant feature was present, but the feature farthest from the goal yielded lower accuracy than one closer. Participants trained with features spontaneously encoded the geometric information. However, this representation did not withstand orientation transformations.