Red and grey squirrels are famed for stashing nuts to make it through winter, but first they must select the right ones: squirrelling food away is a waste of effort if it’s not nutritious and in good condition. The rodents recognise ripe nuts by smell, much as we tell a ripe melon from one that’s hard and tasteless.
Squirrels also reject acorns and hazelnuts that have been hollowed out by weevils, whose larvae develop inside the protective shell. By handling these dud nuts, the animals recognise that they are too light, tossing them aside – experiments show that hollowed-out nuts filled with plaster will fool squirrels into storing them away.
In an autumn when food is abundant, squirrels have plenty of spare time to collect nuts one at a time in their mouth. They scrape a small hole in soft earth and bury their prize, patting the soil down on top to hide it from birds.
Squirrels use a combination of cues to find them again later. First, the caching is not random. A particular place will have been chosen – under a big oak, for example – and remembered. Also several squirrels may use the same patch, which increases the probability that they will find stored nuts simply by chance.
When a squirrel returns weeks later, it peers at the ground, looking for disturbed soil and sniffing to detect a nutty smell. This multi-sense inspection focuses digging on the spots most likely to yield a nut. Any that are missed develop into new trees, benefiting future generations.
Did you know?
Squirrels can even sniff out stored nuts under a layer of snow.
Greys spend more time foraging on the ground than reds, so exploit a much wider selection of foods.
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