Use of a geometric rule or absolute vectors: landmark use by Clark's nutcrackers (Nucifraga columbiana).

Clark's nutcrackers (Nucifraga columbiana) were trained to search for a hidden goal located in the center of a four-landmark array. Upon completion of training, the nutcrackers were presented with tests that expanded the landmark array in the east-west direction, north-south direction and in both directions simultaneously. Although the birds learned to search accurately at the center of the landmark array during training, this search pattern did not transfer to the expansion tests. The nutcrackers searched at locations defined by absolute distance and/or direction relationships with landmarks in the training array. These results contrast with those from experiments with nutcrackers in which an abstract geometric rule was learned. This difference appears due to differences in the experimental paradigms used during training.

Way-finding and landmarks: the multiple-bearings hypothesis.

Clark's nutcrackers (Nucifraga columbiana) are capable of very precise searching using the metric relationships between a goal and multiple landmarks to relocate the goal location. They can judge the direction more accurately than the distance to a landmark when the landmark is distant from the goal. On the basis of these findings, we propose that nutcrackers use a set of bearings, each a measure of the direction from the goal to a different landmark, when searching for that goal. The results of a simulation demonstrate that increasing the number of landmarks used results in increasingly precise searching. This multiple-bearings hypothesis makes a series of detailed predictions about how the distribution of searches will vary as a function of the geometry of the locations of the relevant landmarks and the goal. It also suggests an explanation for inconsistencies in the literature on the effects of clock-shifts on searching and on homing.

Geometric rule learning by Clark's nutcrackers (Nucifraga columbiana).

Clark's nutcrackers (Nucifraga columbiana) were trained to search in a location defined by its geometric relationship to 2 landmarks. Two groups were trained to search at different points along the line connecting the landmarks, and 2 groups were trained to find the 3rd point of a triangle, on the basis of either direction or distance from the landmarks. All groups learned and transferred to new interlandmark distances. However, the constant-distance group learned more slowly, searched less accurately, and showed less transfer than the other 3 groups. When tested with new orientations of the landmarks, the birds tended to follow small but not large rotations. When tested with a single landmark, birds in the half, quarter, and constant-bearing groups searched in the appropriate direction from the landmark, but birds in the distance group did not. These results demonstrate that nutcrackers can learn a variety of geometric principles, that directional information may be weighted more heavily than distance information, and that the birds can use both absolute and relative information about spatial relationships.

Sociality and social learning in two species of corvids: the pinyon jay (Gymnorhinus cyanocephalus) and the Clark's nutcracker (Nucifraga columbiana).

The hypothesis that social learning is an adaptive specialization for social living predicts that social species should learn better socially than they do individually, but that nonsocial species should not exhibit a similar enhancement of performance under social learning conditions. The authors compared individual and social learning abilities in 2 corvid species: the highly social pinyon jay (Gymnorhinus cyanocephalus) and the less social Clark's nutcracker (Nucifraga columbiana). The birds were tested on 2 different tasks under individual and social learning conditions. Half learned a motor task individually and a discrimination task socially; the other half learned the motor task socially and the discrimination task individually. Pinyon jays learned faster socially than they did individually, but nutcrackers performed equally well under both learning conditions. Results support the hypothesis that social learning is an adaptive specialization for social living in pinyon jays.

Differences in hippocampal volume among food storing corvids.

The hippocampal complex (hippocampus and parahippocampalis) is known to play a role in spatial memory in birds and is known to be larger in food-storing versus non-storing birds. In the present study, we investigated the relative volume of the hippocampal complex in four food-storing corvids: gray-breasted jays (Aphelocoma ultramarina), scrub jays (Aphelocoma coerulescens), pinyon jays (Gymnorhinus cyanocephalus), and Clark's nutcrackers (Nucifraga columbiana). The results show that Clark's nutcrackers have a larger hippocampal complex, relative to both body and total brain size, than the other three species. Clark's nutcrackers rely more extensively on stored food in the wild than the other three species. Clark's nutcrackers also perform better during cache recovery and operant tests of spatial memory than scrub jays. Thus, greater hippocampal volume is associated with better performance in laboratory tests of spatial memory and with stronger dependence on food stores in the wild.

Performance of four seed-caching corvid species in operant tests of nonspatial and spatial memory.

The performance of 4 seed-caching corvid species was tested using 2 different operant nonmatching tasks. These species differ in their dependence on stored food, and differences in spatial memory tests have been correlated with better performance by the more cache-dependent species. Acquisition and retention of a color non-matching-to-sample task was tested in Experiment 1. Acquisition of the color task was not correlated with cache dependence, and no differences between species in performance during memory testing were found. Acquisition and retention of an operant spatial non-matching-to-sample task was tested in Experiment 2. Species differences in the spatial task were found for acquisition and during retention testing. The influence of natural history on the evolution of memory is discussed.

Performance of four seed-caching corvid species in the radial-arm maze analog.

Four seed-caching corvid species were tested in an open-room analog of the radial-arm maze. During Experiment 1, the species more dependent on stored food. Clark's nutcrackers (Nucifraga columbiana) and pinyon jays (Gymnorhinus cyanocephalus), acquired the task more quickly and to higher accuracy levels than either scrub jays (Aphelocoma coerulescens) or Mexican jays (A. ultramarina). During Experiment 2, performance after retention intervals was tested. When intervals of 30-210 min were tested in ascending order, species differences observed during acquisition were again obtained. However, when intervals of 5-300 min were tested in random order, the species differed only at shorter intervals. During Experiment 3, only nutcrackers gave any indication of performing above chance after a 24-hr retention intervals. Results support the hypothesis of species differences in spatial information processing that correlate with dependence on stored food.

Effects of response strategy and retention interval on performance of Clark's nutcrackers in a radial maze analogue.

Two groups of Clark's nutcrackers (Nucifraga columbiana) were trained to use either a stay or shift response strategy in a radial maze analogue. Each trial had a preretention stage, a retention interval, and a postretention test. In Experiment 1, acquisition with a 5-min retention interval was studied. Response strategy did not affect the rate at which the task was learned. Performance following longer retention intervals was tested in Experiments 2-4. Changes in retention intervals were presented in trial blocks of increasing duration in Experiment 2 and were randomly presented between trials in Experiment 3. Experiment 4 extended the retention interval to 24 hr. No difference in performance was found between the 2 groups in any of these experiments. These results suggest a flexible relationship between spatial memory and response requirement in food-hoarding birds for at least 1 spatial memory task.

Spatial learning as an adaptation in hummingbirds.

An ecological approach based on food distribution suggests that humming birds should more easily learn to visit a flower in a new location than to learn to return to a flower in a position just visited, for a food reward. Experimental results support this hypothesis as well as the general view that differences in learning within and among species represent adaptations.

Search Image Formation in the Blue Jay (Cyanocitta cristata).

Blue jays trained to detect Catocala moths in slides were exposed to two types of slide series containing these moths: series of one species and series of two species intermixed. In one-species series, detection ability increased with successive encounters with one prey type. No similar effect occurred in two-species series. These results are a direct demonstration of a specific search image.

Visual Detection of Cryptic Prey by Blue Jays (Cyanocitta cristata).

Blue jays learned to respond differentially to the presence or absence of Catocala moths in slides. This detection of the moths by the jays was affected by the background upon which the moth was placed and its body orientation, thus providing an objective measure of crypticity. These procedures are useful for the study of visual detection of prey.

Tool-making and tool-using in the northern blue jay.

Laboratory-raised Northeirn blue jays (Cyanocitta cristata) have been observed tearing pieces from pages of newspaper and utilizing them as tools to rake in food pellets which were otherwise out of reach. The frequency of this behavior was dependenit upon the motivational state of the jay and the presence of food pellets.

Three-configuration matching-to-sample in the pigeon.

Pigeons were trained on a zero-delay matching-to-sample procedure during which only three of the four possible stimulus configurations were presented. Subsequently, all birds were exposed to all four configurations as a transfer test. A high degree of negative transfer from the three training configurations was obtained in Experiment 1. The results of Experiment 2 indicated that three-configuration training produced differential position-preference effects. During the transfer test, responding after one sample stimulus was apparently based on position, while responding after the other sample was based on color.