How do squirrels find buried nuts?
Squirrels bury nuts for future consumption, sometimes many months away. I recently learned that tree squirrels, including Eastern grey squirrels, sometimes dig empty holes, pretend to drop nuts in them, then cover them back up. It's a behavior which is generally called either "tactical deception" or "deceptive caching." It takes place in all squirrel habitats, including backyards, forests, and anyplace where food is available.
Squirrels do this so that other squirrels, or nut-loving animals, will spend time digging in a recognizable hole, only to find it empty. If squirrels can be deceived in this way, then how do they know where nuts really are? There has to be something to it other than random digging, which seems especially hard to believe in large forests.
How do squirrels actually find nuts, either buried by themselves or by others?
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1 answer
It looks like its a combination of smell and memory.
Abstract. It has previously been assumed that grey squirrels, Sciurus cqrolinensis, cannot remember the locations of nuts they have buried, and hence must relocate nuts by their odour. This assumption was tested by measuring the accuracy of cache retrieval of captive squirrels. Each squirrel was released alone into an outdoor arena,where it cached 10 hazel nuts. After a delay of 2,4 or 12 days, each squirrel was returned to the arena and tested for its ability to retrieve nuts from its own cache sites and from 10 cache sites used by other squirrels. Although each squirrel's own caches were close to the caches of other squirrels, the squirrels retrieved significantly more nuts from their own sites than from sites used by other squirrels, after all delays. The retrieval accuracy of the squirrels under these conditions indicates that while grey squirrels can locate buried nuts by their odour, they can also remember the individual locations of nuts they have buried.
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A greater .number of a squirrel's own caches ('own') retrieval than caches of other squirrels ('other') relative to the numbers of each cache type available, was taken as positive evidence for memory of cache location.
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Memory of cache locations, even in the absence of competitors or predators, may have additional adaptive value if it increases a squirrel's retrieval efficiency. The squirrels in this study appeared to minimize their retrieval searcli paths by running directly from one patch oftrvo or three caches to the next, harvesting the caches r"ith little ;e-tracing of their path; this can be seen in the sequence of retrievals illustrated in Fig. l. If so, this would indicate that grey squirrels, like chimpanzees Pan troglodytes (Menzel, 1973), can remember a series of locations in relation to each other and use this information to form a cognitive map, where information about cache sites may be encoded
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An interesting implication of these results is that the squirrels employed two methods to find caches: they returned to sites where they had buried nuts and they searched for the odour of buried nuts. Under the conditions of this experiment, either the first method was used more often than the second, or it succeeded more often. Perhaps these methods are used simultaneously: squirrels might sniff the ground for odour cues while they are orienting to the locations of remembered cache.
Grey squirrels remember the locations of buried nuts
There was also a study that found that the squirrels were organizing their nuts to make them easier to remember and find when gathered from a single source.
Squirrels either collected each nut from a different location or collected all nuts from a single location; we then mapped their subsequent cache distributions using GPS. The chunking hypothesis predicted that squirrels would spatially organize caches by nut species, regardless of presentation order. Our results instead demonstrated that squirrels spatially chunked their caches by nut species but only when caching food that was foraged from a single location. This first demonstration of spatial chunking in a scatter hoarder underscores the cognitive demand of scatter hoarding.
Caching for where and what: evidence for a mnemonic strategy in a scatter-hoarder
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