Western European Hedgehog (Erinaceus europaeus) Natural history The European hedgehog (Erinaceus europaeus) is commonly associated with humans in rural, suburban, and urban habitats. Its native range spans from Ireland, Great Britain, southern Scandinavia, and Western Europe to the Czech Republic, where its range overlaps with that of the Northern white-breasted hedgehog (Erinaceus roumanicus). In addition to its native range, E. europaeus was introduced in 1974 to the Scottish island of Uist and in the late 19th Century to New Zealand, where it is considered an invasive pest species. European hedgehogs are nocturnal animals, and their dominant senses are hearing and olfaction. Hedgehogs prefer habitats that provide cover like hedgerows, shrub borders in suburban gardens, and leaf litter. Hedgehogs tend to avoid thick forests, although they will use forest edge habitat. Adult hedgehogs are solitary, but they may share overlapping home ranges. Each home range is large, and hedgehogs can travel approximately 3-4 km (1.9-2 miles) each night. Each hedgehog builds several nests within its home range, concealing itself in a nearby nest at the end of a night’s foraging. Sharp spines that cover the dorsum and sides as well as the ability to roll up serve as a highly effective defense mechanism against predators. European hedgehogs have few natural predators, with the badger likely serving as their most important. Other known predators include dogs, foxes, snakes and large owls. Conservation status The International Union for Conservation of Nature lists Erinaceus europaeus as a species of “Least Concern” because animals are common and abundant throughout its wide range (Amori 2008). Taxonomy Class: Mammalia Order: Erinaceomorpha: gymnures and hedgehogs Family: Erinaceidae Subfamily: Erinaceinae: spiny hedgehogs Genus: Erinaceus: woodland hedgehogs Genus: Erinaceus europaeus   Physical description The dorsal surface and sides of the European hedgehog are covered in pale spines that have a wide brown band and a white tip. The spines are relatively long, measuring 1.9-2.5 cm (0.75-1 in) in length. The face, throat, chest, abdomen, and legs are covered with coarse, grey-brown or yellow-brown fur. Head and body length of the adult hedgehog averages 20-30 cm (7.8-11.8 in). Males are generally larger than females, however the presence of a prepuce on the mid-ventral abdomen is the best means of gender identification. Diet The European hedgehog is primarily insectivorous. Insects frequently eaten by free-ranging animals include beetles, caterpillars, earwigs, flies, and centipedes, however European hedgehogs can be more omnivorous and somewhat opportunistic in their feeding behavior. Therefore the diet also includes snails and slugs, earthworms, woodlice, mollusks, and sometimes small vertebrates like frogs, toads, snakes, birds and their eggs, as well as small mammals in the form of carrion. The bulk of most captive adult diets consist of a protein source such as meat-based dry or canned cat or dog/puppy food (free of gravy), and/or specialist hedgehog food. Some rehabilitators add a commercially available diet for insect-eating songbirds. Some rehabilitators also mix the protein source with a small amount of crushed, unsweetened cereal (oat, bran, moistened muesli, or whole grain wheat). The diet may also be supplemented with a multivitamin and/or even a pancreatic enzyme supplement to aid digestion and promote a more rapid build-up of body reserves, particularly in underweight juveniles. Offer food once or twice daily to most adults (British Hedgehog Preservation Society 2013, Pfäffle 2010, Robinson 2002, British Hedgehog Preservation Society year unknown). A once daily ration, offered in the evening to these nocturnal animals, may reduce the risk of obesity in healthy animals (Bexton 2003). Treats can include fresh fruit such as banana, raisins and sultanas, dry cat or hedgehog kibble, unsweetened crushed “digestive biscuits” (hard, cereal-based treats), or small amounts of cooked chicken or raw liver (British Hedgehog Preservation Society 2013, British Hedgehog Preservation Society year unknown). NEVER offer cow’s milk as hedgehogs cannot digest lactose (Bexton 2003). Husbandry Water Provide fresh water daily. Heavy crocks can be offered to prevent tipping. Ensure the water level is shallow enough to prevent accidental drowning and cleaned frequently, as hedgehogs tend to foul water bowls with shavings or other cage bedding materials. Cage design Important housing criteria include: Space:  Provide the largest enclosure reasonably possible that affords the hedgehog opportunities to hide, forage, and build nests measuring at least 30-60 cm (1-2 ft.) in diameter. Unless hibernating, long-term patients should ideally not be retained in small pens as a percentage of hospitalized hogs exhibit obsessive caged behaviors (Tim Partridge, email message to author, May 3, 2015). Nest box: Offer a high-sided nesting box lined with newspaper and filled with abundant, soft, absorbent bedding such as straw, hay, or wood shavings. Avoid cloth or toweling as loose strings can cause injury if ingested or caught on toes or toenails. Facial tissues and paper towels can also be added to the nest box. Shelters can be made from any material that can be sanitized like plastic or disposable cardboard boxes can be provided. Smooth-walled:  Pens should ideally have high, smooth walls to prevent escape. Smooth walls and flooring also reduce the risk of injury to toes or limbs. Escape prevention:  Walls should be high and the walls of outdoor pens should be buried approximately 30 cm (1 ft) underground to prevent burrowing and escape. Cage furniture High-sided nest box (see cage design above) Ceramic radiant heat lamp (see temperature below) Heavy crock dishes for food and water Temperature Maintain environmental temperatures for adults between 21-30°C (70-85°F) (Tynes 2010). During cool weather, place a ceramic radiant heat lamp over one end of the enclosure to create a temperature gradient. Place the nesting area at the warm end of the enclosure and provide food in a slightly cooler area. Maintain temperature above 10°C (50°F) to prevent the beginning of a hibernation cycle.House hoglets in an incubator set at 30°C (86°F) (Robinson 2002). Gradually reduce the setting to room temperature when body weight is between 150-200 g. Hibernation Hibernation in the European hedgehog occurs at temperatures below 8°C (46.6°F). Depending on the region, hibernation begins between September and November and lasts until sometime between March to May. Free-ranging hedgehogs construct a dense hibernaculum to ensure a constant environmental temperature of 1-5°C (34-52°F). Variations in hibernation patterns are primarily related to insufficient storage of fat reserves during late summer and fall. A juvenile hedgehog must weigh approximately 500 g to survive its first hibernation. Up to 80% of free-ranging adults can die during the frigid winter months. Behavior Nocturnal European hedgehogs are nocturnal animals and activity during daylight is usually a sign of illness or inability to find enough food during the night. Social structure Hedgehogs are solitary creatures with a social structure that is sometimes compared to the cat. Hedgehogs possess overlapping home ranges that they do not defend. Instead they are theorized to use olfactory cues and a system of mutual avoidance.House captive hedgehogs in individual pens or cages, unless the animals are presented as littermates. When multiple captive hedgehogs must be housed together, aggression can arise but is very uncommon. To minimize the risk of fighting, provide as much space as possible as well as multiple shelters, feeding stations, and water bowls to reduce the likelihood of aggression. Reproductive behavior Hedgehogs are solitary creatures except during their mating season. Sexual behavior begins directly after hedgehogs rouse from hibernation, however most sexual activity takes place between May and August. Fighting is often observed in males during the mating season, however females can also behave aggressively towards courting males. European hedgehogs are polygynandrous (promiscuous ) and polygamous, therefore females mate with more than one male and males breed with more than one female. Males are not involved in raising offspring. Defensive behavior When threatened, hedgehogs will usually display passive defense behavior by freezing and rolling up, thus exposing only their erect spines to a would-be predator. Hedgehogs sometimes display active behavior like jumping with erect spines. Hedgehogs will snort or hiss when disturbed, and this should not be mistaken for respiratory abnormalities. Self-anointing Self-anointing or “anting” is an unusual hedgehog habit in which the hedgehog will start to produce copious amounts of foamy saliva that is then slathered onto the spines of the flank and back with its tongue. Although many theories exist, the true purpose of ‘self-anointing’ is still a mystery, although this behavior seems to be triggered by novel scents or flavors (D’Havé 2005) Normal physiologic data Lifespan Free-ranging European hedgehogs generally live 3-4 years, however the maximum lifespan reported is 8 years. In captivity, hedgehogs can live up to 10 years. Body weight The weight of the average adult hedgehog ranges between 700-1400 g. Pre-hibernation weights between 600-1000 g are common, however bodyweight normally increases dramatically in preparation for hibernation. Adult males range from 800-1200 g (Tynes, 2010, Johnson-Delaney 2008, Johnson-Delaney 2007). Adult females range from 400-800 g (Johnson-Delaney 2008, Johnson-Delaney 2007). To survive hibernation, a hedgehog should attain a minimum weight of 450-600 g. Post-hibernation weight loss may reach up to 35% (Pfäffle 2010). Body temperature The European hedgehog rectal temperature averages 35.1°C +/- 1°C (95.2°F). Heart rate Heart rate averages 200-280 beats per minute (bpm), however rates as low as 2-48 bpm have been reported during hibernation. Respiratory rate 25-50 breaths per minute (bpm) is the average respiratory rate. Respirations decreases to approximately 13 bpm during hibernation (Pfäffle 2010), however hibernating hedgehogs may reportedly be apneic for up to 1 hour (British Hedgehog Preservation Society, year unknown). Anatomy/ physiology Dental formula, adult I3/2 C1/1 P3/2-3 M3/3* Integumentary Hedgehogs possess a specialized coat of approximately 5,000-7,000 spines. Each spine, or modified hair, grows from a follicle in the skin. Each follicle is attached to a small muscle (arrector pili) that is used for piloerection when the hedgehog is threatened. The spines are hollow and sharp, but not barbed. Unlike porcupines, hedgehog spines do not break off readily and they do not bend easily. Hedgehogs generally replace spines in a gradual, continuous process  (Tynes 2010). Musculoskeletal Well-developed back muscles allow hedgehogs to roll up in a defensive ball. The panniculus carnosus is a sheet of muscle that spreads over the back. The circular orbicularis muscle acts like a purse string to close the ball and protect the vulnerable head, legs, feet, and abdomen. Specialized modifications to the intervertebral disks and vertebral processes also assist the hedgehog in rolling up (Pfäffle 2010, Tynes 2010, Robinson 2002). Sexual dimorphism The male is generally larger however the presence of a prepuce on the mid-ventral abdomen is the best means of determining gender. Reproduction The vulva is positioned directly anterior to the anus, while the penis sheath of the male lies on the mid-ventral surface of the abdomen. Puberty:   Males: 8 months to 1 year Female: 8-9 months On average, European hedgehogs reach sexual maturity between 9-11 months of age. Body weight may be the best predictor of sexual maturity. In one study of captive European hedgehogs, most females did not become pregnant while weighing less than 600 g and most weighed more than 700 g before becoming pregnant for the first time (Tynes 2010). Reproductive behavior:  See Behavior above Gestation:  4-5 weeks (average 35 days) One or two litters are produced annually, one in spring and one in late summer. If a second litter is born, it has a reduced chance of surviving the winter. Litter size:  Litter sizes of four to five are common in European hedgehogs, however up to six hoglets can be born. Birth weight:  A range of 8-25 grams has been reported, with an average of 15 g reported in captivity. Eyes open:  12-14 days; both eyes and ears should be open by about 15 days of age Deciduous teeth eruption:  21-23 days (100 g); the last deciduous teeth are lost at 4 months Permanent teeth eruption:  7-9 weeks (250-300 g) Weaning:  Most young hedgehogs are fully weaned by 40-44 days, although some may be weaned as late as 10 weeks. Weaning weights at 40 days range from 125-345 g (average 200-235 g).  Youngsters leave the nest and go on foraging expeditions with their mother at 3-5 weeks (100-200 g). Juveniles become independent by 4-6 weeks (> 250 g). *Variations in the dental formula in the European hedgehog have been described in the literature (Asher 2009, Robinson 2002). Here Dr. Timothy Partridge describes dental evaluation of anesthetized healthy, young adults : “It appears there are…a total of six premolars and molars on the lower arcades of (almost […]