European Hedgehog Behaviour - Running in Circle & Learning

Running in Circles

Self-anointing may not be a behaviour unique to hedgehogs, but running or walking in circles may well be. Most popular hedgehog books make mention of the well-documented, but infrequently witnessed, phenomenon of apparently healthy hedgehogs running in circles, sometimes for hours on end, without seeming to get bored or tire. In a paper to the Journal of Zoology in 1967, the late Cambridge University theologian John Sandwith Boys Smith described one such instance. Boys Smith wrote of how, over a period of several nights in May, a hedgehog of unknown sex ran anticlockwise at a steady speed of about 4.5 mph (about 7 kmph) in a 46 ft (14 m) diameter circle for more than two hours in his garden at St John’s College. If we assume a constant speed, a constant diameter and a constant two hours of activity then the hedgehog ran around this circle 303 times; a distance of some 13 km (9 miles). When not running, Boys Smith noted that the hedgehog behaved and foraged normally and it is particularly curious that the hog would leave its daytime nest and run straight to the northern end of the garden to commence running.

A Northern white-breasted hedgehog (Erinaceus roumanicus) running in circles on the edge of a road during the day in the Czech Republic, stopping to scratch and shake before carrying on. The cause of this curious behaviour remains a mystery. - Credit: Tomáš Kurucz.

This behaviour was subsequently mentioned in an issue of The Observer newspaper at the time and prompted a reader to write in to recount a similar, if an even more bizarre, behaviour they had witnessed while crossing some rough grassland at dusk during the summer. On page 39 of Sunday 28th January 1968’s edition of The Observer, under the heading “Hedgehogs Again”, their correspondent for Inverness wrote:

Advancing slowly, I discovered five or six hedgehogs walking in a circle with irregular spacing between them and grunting away merrily. They appeared to have been on the move for some time, as the circle (about fifteen feet diameter) was well trampled.

These hedgehogs were apparently moving clockwise and the observer suggested it may have been courtship. Indeed, hedgehogs do snort and grunt during courtship, as well as during aggressive encounters. Unfortunately, it is so rarely observed that it has yet to be formally studied and the cause of these behaviours remains a mystery. In his New Hedgehog Book, Pat Morris suggests, albeit tentatively, this may be an aberrant behaviour resulting from illness (perhaps an inner ear imbalance) or pesticide poisoning; that this behaviour has only been documented post-1960, when relatively large amounts of garden pesticides have been used, might provide some support for the latter. Equally, however, the behaviour may have simply gone unnoticed prior to 1960. Furthermore, neither explanation really explains the periodicity of the behaviour.

A European hedgehog running in circles on a track in Denmark. - Credit: Jan Dyrby Kristensen

Assuming Boys Smith, for example, was observing the same hedgehog and not just assuming it was the same one, it would be curious for an illness or poisoning to come and go over the course of only a few hours. In his 1969 book, The Hedgehog, Maurice Burton mentioned one tame hedgehog that took to running in small circles each night before it died; he considered some form of brain disorder was the most likely cause. Off-hand, it would seem an unhealthy behaviour given that it invariably burns a great deal of energy while at the same time preventing the animal from eating or drinking.

Learning

The brain of the European hedgehog showing well developed olfactory lobes (paired at the front). The "encephalization quotient", a measure of the relative brain size compared to the expected mass for an "average" mammal of this size, is low for hedgehogs, implying hedgehogs aren't as "brainy" as their more specialised relatives, such as moles. [Preparation of this image was funded by the National Science Foundation & National Institutes of Health.] - Credit: University of Wisconsin & Michigan State Comparative Mammalian Brain Collections

It is perhaps observations of hedgehogs running in a circle more than 300 times before continuing its nightly foraging that have fuelled the idea that hedgehogs are not the smartest of animals. Indeed, while the olfactory lobes of the brain are well developed (with complex olfactory circuits), the cerebral hemispheres are fairly unelaborated and lack the ridges found in other “higher” vertebrates, like birds and primates. Moreover, some behavioural experiments seem to suggest hedgehogs lack the same learning abilities of other species such as rats, birds, sharks and primates.

In one oft-cited example, a man who was trying to teach his pet hedgehog to associate a red door with food gave up after the four-thousandth attempt. Similar experiments have, however, been more successful and, provided the colour (black or white) is not changed, hedgehogs can be taught to choose the appropriate option for food. Nonetheless, in his New Hedgehog Book, Pat Morris suggests that the overcoming of particularly difficult challenges is probably luck.

The observations that some hedgehogs would come when called, or could be taught to discriminate shapes and symbols to a limited degree imply some form of rudimentary learning and memory capacity. Indeed, Morris mentions that hedgehogs typically seem to have a good memory, remembering associations for several months, that doesn’t appear to be adversely impacted by hibernation. It is worth mentioning that a hedgehog lacking the more advanced learning and memory capacity observed in birds and primates is not particularly surprising. Generally, such ‘intelligence’ arises to cope with the complex dynamics of sociality. Hedgehogs are largely asocial and, as such, they probably don’t require such advanced brain development. Nonetheless, as John Eisenberg argues in his contribution to Comparative Physiology: Primitive Mammals, it should not be assumed that brief social interactions are necessarily less complex than the similar interactions in more ‘advanced’ mammals.