Cache Events Research Articles

Observational visuospatial encoding of the cache locations of others by western scrub-jays (Aphelocoma californica)

Western scrub-jays (Aphelocoma californica) hide food and rely on spatial memory to recover their caches at a later date. They also rely on observational spatial memory to steal caches made by other individuals. Successful pilfering may require an understanding of allocentric space because the observer will often be in a different position from the demonstrator when the caching event occurs. We compared cache recovery accuracy of pairs of observers that watched a demonstrator cache food. The pattern of recovery searches showed that observers were more accurate when they had observed the caching event from the same viewing direction as the demonstrator than when they had watched from the opposite direction. Search accuracy was not affected by whether or not the tray-specific local cues provided left–right landmark information (i.e. heterogeneous vs. homogeneous local cues), or whether or not the caching tray location was rotated. Taken together, these results suggest that observers have excellent spatial memory and that they have little difficulty with mental rotation.

Food-Caching Western Scrub-Jays Keep Track of Who Was Watching When

Western scrub-jays (Aphelocoma californica) hide food caches for future consumption, steal others' caches, and engage in tactics to minimize the chance that their own caches will be stolen. We show that scrub-jays remember which individual watched them during particular caching events and alter their recaching behavior accordingly. We found no evidence to suggest that a storer's use of cache protection tactics is cued by the observer's behavior.

Elements of episodic-like memory in animals.

A number of psychologists have suggested that episodic memory is a uniquely human phenomenon and, until recently, there was little evidence that animals could recall a unique past experience and respond appropriately. Experiments on food-caching memory in scrub jays question this assumption. On the basis of a single caching episode, scrub jays can remember when and where they cached a variety of foods that differ in the rate at which they degrade, in a way that is inexplicable by relative familiarity. They can update their memory of the contents of a cache depending on whether or not they have emptied the cache site, and can also remember where another bird has hidden caches, suggesting that they encode rich representations of the caching event. They make temporal generalizations about when perishable items should degrade and also remember the relative time since caching when the same food is cached in distinct sites at different times. These results show that jays form integrated memories for the location, content and time of caching. This memory capability fulfils Tulving's behavioural criteria for episodic memory and is thus termed 'episodic-like'. We suggest that several features of episodic memory may not be unique to humans.

CACHE MANAGEMENT BY SMALL MAMMALS: EXPERIMENTAL EVIDENCE FOR THE SIGNIFICANCE OF ACORN-EMBRYO EXCISION

We conducted 2 field experiments to assess relative importance of acorn-embryo excision in the caching decisions of small mammals. In the 1st, we selectively provisioned small mammals with metal-tagged acorns of red oak (Quercus rubra) and white oak (Q. alba) at 40 point locations in 8 sites in an oak forest in northeastern Pennsylvania. We then followed the fate of cached seeds by relocating acorns with metal detectors soon after they were cached and again in spring after seeds began to germinate. At least 1 species of small mammal excised embryos of .70% of the cached acorns of white oak and ,4% of those of red oak. Animals also were observed to revisit caches in spring and excise embryos of germinating acorns. More excised acorns of white oak were found intact in spring than those of red oak, indicating that the behavior is important for long-term storage of these seeds. In a 2nd experiment, we presented free-ranging Mexican gray squirrels (Sciurus aureogaster) with pairs of acorns of 5 native white oak and 5 native red oak species and recorded caching events and whether or not cached seeds had their embryos removed. Squirrels cached significantly more acorns of white oak species, frequently excised embryos of these seeds, and only excised embryos of red oaks when they were germinating. These results support our previous hypothesis that the behavior of embryo excision is geographically widespread and has important implications for cache-management strategies of some diurnal tree squirrels and their effect on dispersal of oaks.

Rapid Effects of Corticosterone on Cache Recovery in Mountain Chickadees (Parus gambeli)

Environmental perturbations increase adrenal activity in several vertebrates. Increases in corticosterone may serve as a proximate trigger whereby organisms can rapidly adapt their behavior to survive environmental fluctuations. In food-caching songbirds, inclement weather may present the need to alter caching and/or retrieval behaviors to ensure food supplies. We hypothesized that corticosterone may increase the rate of caching and/or retrieval behaviors in the mountain chickadee, a food-storing songbird, and tested if these potential effects were mediated by alterations in appetite, activity, or memory for cache sites. Corticosterone or vehicle was administered to subjects 5 min prior to either caching or recovery in a naturalistic laboratory paradigm during which we recorded the number of caching events, sites visited, and seeds eaten (caching) or caches recovered, total sites visited, cache-related visits, and non-cache-related visits (recovery). Data were analyzed using nested ANOVA for treatment within sequential trial. There was no effect on any caching behaviors following treatment. However, birds treated with corticosterone during retrieval recovered more seeds and tended to visit more cache-related sites than did controls. Since groups did not differ in the number of seeds eaten or the total number of sites visited, it seems unlikely that corticosterone affected appetite or activity. Rapid surges in corticosterone may increase the efficacy of an underlying memory process for cache sites which is reflected in higher cache recovery in corticosterone-treated birds than in controls. Thus, rapid alterations in plasma corticosterone following environmental change may alter memory-reliant behaviors which promote survival in the food-caching mountain chickadee.