A disorder with ancient roots?
I think we all know some people who are ever so ready to throw away something they no longer fancy or to discard some item if a newer version is available. But we may also know people, who behave in exactly the opposite way: they never throw away anything but keep and store and guard even things that no longer seem useful. That kind of behaviour can be compared to what is termed “hoarding” and, if compulsive, it is now considered a mental disorder of the “obsessive-compulsive” nature. But is it an atavism, a re-surfacing of an ancient trait with roots in the animal kingdom as suggested by Sandro René Pinto de Sousa Miguel, Rodrigo Ligabue-Braun of Porto Alegre in Brazil, akin to narcolepsy and quadripedalism in humans, which have also been linked to atavisms?
Hoarding, especially of food but occasionally also of material or other items, is certainly common in the animal kingdom and helps individuals survive lean periods. And immediately La Fontaine’s famous poem “La cigale et al fourmi” that I had to learn as a pupil during my High School French lesson, comes to mind. Indeed, there are several examples of invertebrates that store or cache food or, in the case of leaf cutter ants, even collect and tend inedible leaves to grow on them edible fungi. Honey bees are so successful (unlike the equally social hornets) and survive the winter, because they prepare and store food for the cold season. Although not usually overwintering, spiders, too, can often be seen in summer to keep numerous wrapped-up insect prey in their orb-webs for later use.
More obvious hoarders are found amongst our feathered friends and some of them behave seemingly intelligently when they attempt to hide food items and then firstly look around to make sure no other bird observes where they hide their treasures. A behaviour such as this has been reported from Corvus corax ravens by the Austrian researchers T. Bugnyar and K. Kotrschal and also the Eurasian jay Garrulus glandarius by the Cambridge University scientists E.W. Legg and N.S. Clayton. North American woodpeckers are less selfish and establish food stores that are accessible to other wood peckers, but whether shrikes like Lanius collurio allow other shrikes to access the insects, and even small mice and lizards, they store on thorns in the open, I do not know. However, policing food stores such as these, which are visible and in the open would be quite a task. Besides, hoarders with multiple caches (to reduce pilferage) run the risk of forgetting some of their troves, and in the case of forgotten and buried seeds, help spreading trees. A special facet of hoarding is that, which is represented by the New Caledonian crow Corvus moneduloides that bends twigs into hooks to extract grubs from wooden trunks with and then hides and hoards these precious tools.
Proverbial hoarders are the hamsters. It has been reported that European hamsters of the species Cricetus cricetus may have many kg of grain (up to 60 kg !) in their nests – and it’s all for themselves (and their offspring). Packrats and squirrels, too, are well known hoarders and beavers establish food stores that can be used by anyone of their family. Some of the best-studied mammalian hoarders are shrews, especially a species by the name of Blarina brevicauda from the northeastern region of North America. To survive the winter they collect and cache food items in their burrows that can contain seeds and dry fruit, invertebrates and even small mice. It was this species of shrew that the Brazilian researchers, mentioned above, compared obsessive human hoarding with to suggest that the latter was an atavism going back to ancient evolutionary roots. The problem is, human hoarders more often than once, not just hoard food, but inedibles like coins, stamps, toys, clothes, buttons etc., and some are even known to hoard and guard some really weird and useless things like used underwear, smelly socks, cigarette buds, etc. Do animals do that also? Well, in the Statistical Manual of Mental Disorders, 5th edition (DSM-5) such behaviours in humans are now classified as a mental disorder. Maybe it’s risky then to mention I collect coins with animals on them.
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