For the most part, erinaceids are nocturnal; although the Malayan moonrat (Echinosorex gymnura) and lesser gymnure (Hylomys suillus) may also forage by day. Species living in temperate zones may be forced to begin foraging before sunset in mid-summer. As a general rule, erinaceids are terrestrial, living and feeding at ground level. Most are competent climbers and swim well—E. gymnura may even be least partially aquatic. Digging ability varies, but some species, such as the Indian and the long-eared hedgehogs (Paraechinus mi-cropus and Hemiechinus auritus) are very good burrowers.

Most members of the Erinaceidae are able to enter torpor and thus tolerate bad weather and seasonal food shortages by hibernating in winter or estivating during droughts. Hibernation of the European hedgehog, (Erinaceus europaeus), in colder parts of its range may last six or seven months, during which the heart rate drops from about 188 beats per minute to around 22, and body temperature may fall to just 1°C (34°F). Prolonged hibernation puts enormous strain on the animals reserves of stored fat and those that do not put on enough weight in the fall will not survive.

All the well-studied species are essentially solitary and territorial as adults. Small groups of three or four have been reported for some species, but these probably represent females with subadult young of the year. Fights are seemingly rare, but individuals may react aggressively to threats, giving rapid hissing snorts. Interestingly, an almost identical sound is pro-

A western European hedgehog (Erinaceus europaeus) on a lawn in Surrey, England. (Photo by Stephen Dalton/Photo Researchers, Inc. Reproduced by permission.)
A central African hedgehog (Atelerix albiventris) peering out from its log den. (Photo by © Joe McDonald/Corbis. Reproduced by permission.)

duced by female hedgehogs during courtship, presumably in response to close approach of another individual, the male.

All erinaceids use scent to mark their home range, but olfactory cues appear to be particularly important for the gymnures, several of which have a strong musky odor that is obvious even to the human nose. Among the other senses, hearing is apparently most sensitive, while eyesight is not particularly acute. One of the most distinctive and unusual aspects of erinaceid behavior is "self-anointing," an activity performed by all species of hedgehog. Apparently triggered by olfactory cues such as strong-smelling or noxious plants or chemicals, this behavior starts with the animals licking or chewing the source of the smell, and producing copious amounts of frothy saliva. The saliva (and presumably with it the chemical trigger, whatever it may be) is then spread over the spines with quick flicks of the tongue and distinctive jerking movements of the head. Presumably the spines provide a surface area from which scent can be dispersed, but so far there is no really satisfactory explanation for the function of self-anointing. Theories range from attracting mates to deterring predators or repelling parasites, but none stand up to rigorous investigation or satisfactorily account for the diver-

A western European hedgehog (Erinaceus europaeus) crossing a small brook. (Photo by Animals Animals ©Robert Maier. Reproduced by permission.)

sity of trigger substances or the wide range of situations in which animals will suddenly devote all their attention to this odd behavior.

Gymnures are relatively secretive animals, while hedgehogs, with the benefit of their spiny defenses, are more bold. When a hedgehog is threatened, it curls itself into a tight ball by means of well-developed abdominal muscles that act like the cord on a drawstring bag. The head, feet and tail are all tucked away and the spines are erected, presenting a potential predator with nothing but a puzzling spiky ball. Some predators, including badgers and foxes, learn the art of unrolling hedgehogs and may become specialist hedgehog eaters.

Western European hedgehog (Erinaceus europaeus) babies sleeping in their nest. (Photo by Animals Animals ©Robert Maier. Reproduced by permission.)
A southern African hedgehog (Atelerix frontalis) devouring a lizard. (Photo by Animals Animals ©Anthony Bannister. Reproduced by permission.)

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