The effect of proximity on landmark use in Clark's nutcrackers.

Clark's nutcrackers, Nucifraga columbiana, store thousands of pine seeds during the autumn and retrieve them throughout the winter. It has been shown that these birds are able to use visual cues to relocate hidden food in the laboratory. In this set of experiments, we trained three groups of Clark's nutcrackers to find a hidden food goal that was placed in the same spatial location relative to the testing room. During training, the location of two local cues in relation to the goal differed between the three groups. Group 1 learned the task with the cues closest to the goal, group 2 with the cues further from the goal, and group 3 with the cues furthest from the goal. To test whether the proximity of these two local cues to the goal affected how spatial information was used, we manipulated local and global information in a series of experiments. Results indicated that local cues were more important sources of spatial information for group 1, whereas global cues seemed to be used more by birds in groups 2 and 3. These findings suggest that the proximity of visual cues lead to overshadowing of other sources of spatial information surrounding the goal. Copyright 1999 The Association for the Study of Animal Behaviour.

Patterns of movement and orientation during caching and recovery by Clark's nutcrackers, Nucifraga columbiana.

Clark's nutcrackers regularly store large numbers of pine seeds and remember the locations of the cached seeds. Although they are very accurate, they do make some errors during recovery. In an attempt to determine whether any behaviours during caching predicted the occurrence of errors during recovery, we videotaped Clark's nutcrackers while they cached and recovered seeds under laboratory conditions. We used the videotapes to develop complete, quantitative descriptions of caching and recovery behaviour, with an emphasis on body orientation and directions of movement. During caching, the birds showed the greatest change in their orientation and direction following cache creation. During cache recovery, in contrast, body orientation changed most following successful recovery of a seed. When orientation while making a cache was compared with orientation when recovering the same cache, orientations were similar more often than would be expected by chance. However, this consistency of direction was not related to the accuracy of cache recovery, indicating that such consistency is not necessary for accurate cache recovery. The location in which the birds chose to place their caches was the only variable that predicted the location of probes during recovery. Copyright 1999 The Association for the Study of Animal Behaviour.

The effect of background cuing on prey detection.

Studies of prey detection have typically focused on how search image affects the capture of cryptic items. This study also considers how background vegetation influences cryptic prey detection. Blue jays, Cyanocitta cristata, searched digitized images for two Catocala moths: C. ilia, which is cryptic on oak, and C. relicta, which is cryptic on birch. Some images contained moths while others did not. The ability of blue jays to detect prey during repeated presentations of one prey type within a session was compared with their performance during randomly alternating presentations of both prey types within a session to examine search-image formation under two background conditions (informative and ambiguous). In the informative background condition, both trees in the image were of the same species and therefore, the background was a reliable indicator of which prey type might be present. In the ambiguous background condition, there was one tree of each species in the image and either prey type could be present. The results indicate that: (1) a search-image effect was observed only for the more cryptic prey type and only when the background was informative; (2) as accuracy on prey images (those with moths) increased, response latency remained unchanged; (3) performance on nonprey images (those without moths) was primarily determined by the difficulty of searching the background and not by the prey type in the accompanying prey images; and (4) search-image effects disappeared with extended practice. These results suggest that the ability to detect prey is influenced by background and that the presence of either multiple backgrounds or multiple prey types interferes with search-image formation. Copyright 1998 The Association for the Study of Animal Behaviour.