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DETAILED PHYSIOLOGY - Editorial Comment

Editorial Comment (Editorial Overview Text Replicated on Overall Species page - Erinaceus europaeus - West European Hedgehog)

METABOLISM (TEMPERATURE):

  • Normal body temperature for hedgehogs is about 35C, peaking at night (0300 hours, 3 am) and dropping to a minimum at 1500 hours (3 pm).
  • Normal temperature for unweaned hoglets is slightly lower than that of adults at about 31.5-34C.
  • During hibernation body temperature drops to close to environmental temperature and may be about 2-5C.
  • Hedgehog metabolism is greatly reduced during hibernation reaching a minimum at about 4-5C which is therefore described as the "optimum" hibernation temperature. An increased metabolic demand is seen with higher ambient temperatures (passive increase in body temperature and therefore metabolic rate) as well as with lower ambient temperatures (to prevent freezing).
  • Hedgehogs have large deposits of brown fat in addition to white fat. The white fat, which can account for 1/3 of body weight just before hibernation, provides the constant energy supply to fuel metabolism during hibernation while brown fat is most important for heat generation during arousals from hibernation.
  • If fat stores are insufficient then the hedgehog will not survive hibernation.
  • Elevated levels of serotonin and reduced levels of noradrenaline are thought to be involved in initiation and maintenance of hibernation. Hormone levels change seasonally, for example prolactin levels are elevated during hibernation while thyroxine levels are reduced.

RESPIRATORY SYSTEM (RESPIRATION):

  • The respiratory rate of active hedgehogs is variable and may be 25 breaths per minute when resting rising to 50 breaths per minute during exercise.
  • During hibernation respiratory rates are reduced with periods of apnoea (average about 56 minutes, sometimes as long as 150 minutes) followed by a period of a number (40-50) rapid breaths. In very cold conditions (ambient temperature below freezing) periods of apnoea are reduced or absent.
  • Oxygen consumption is greatly reduced during hibernation, at 5C to only 0.5% of normal resting levels. Oxygen consumption is higher at 10C and at -5C than at 4-5C (the optimum temperature for hibernation).

CIRCULATORY SYSTEM (PULSE/HEART RATE):

  • The heart rate of hedgehogs may be about 147 beats per minute (bpm) for a sleeping hedgehog and 200-280 bpm for an awake hedgehog.
  • In hibernation the rate may drop to 2-12 bpm. All components of the ECG (electrocardiogram) are prolonged in hibernating hedgehogs.
  • A variety of changes occur prior to and during hibernation, for example splenic enlargement and decreases in the water content of muscle, liver and blood (but not of the brain, heart and kidneys).

GASTROINTESTINAL SYSTEM (FAECES AND GUT MOTILITY):

  • Normal hedgehog droppings are cylindrical, about 2-3 cm long and black, dark grey or dark green, usually with visible bits of insect parts on them. Faeces from juveniles are softer than those of adults and greyish green in colour.
  • Gastro-intestinal: Gut transit time is short; most ingesta is passed within 12-16 hours of ingestion. It is thought that only negligible bacterial fermentation occurs in digestion. During hibernation there are changes including involution of mucosal secretory glands.

URINARY SYSTEM (URINE):

  • During hibernation urine production is greatly decreased. Small volumes of urine may be produced and voided during the periods of arousal.

CHROMOSOMES:

MUSCULO-SKELETAL SYSTEM:

SPECIAL SENSES AND VOCALISATIONS:

  • The most important senses to hedgehogs are hearing and olfaction. Their hearing is acute, particularly at high frequencies. Their sense of smell is also highly developed; both are used in detecting prey. Vision is relatively unimportant although hedgehogs are far from blind and even appear to have limited colour vision in good light. Normal behaviour has been recorded in an almost blind radio-tracked hedgehog, although it did bump into objects. Hedgehogs appear to have a well developed sense of taste. The vomeronasal organ (Jacobson's organ) is well developed and functional. They also possess a few long tactile sensory hairs on the snout. They do not use echolocation.
  • Hedgehogs produce a range of sounds including squeaking and whistling by hoglets, loud snuffling while foraging, puffing snorts during courtship and quarrels, loud chattering sounds (probably made by the teeth) and a high pitched scream in severe pain or distress.

(References are available in detailed literature reports below)

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Metabolism (Temperature)

Source Information SUMMARY:
  • Normal body temperature for hedgehogs is about 35C, peaking at night (0300 hours, 3 am) and dropping to a minimum at 1500 hours (3 pm).
  • Normal temperature for unweaned hoglets is slightly lower than that of adults at about 31.5-34C.
  • During hibernation body temperature drops to close to environmental temperature and may be about 2-5C.
  • Hedgehog metabolism is greatly reduced during hibernation reaching a minimum at about 4-5C which is therefore described as the "optimum" hibernation temperature. An increased metabolic demand is seen with higher ambient temperatures (passive increase in body temperature and therefore metabolic rate) as well as with lower ambient temperatures (to prevent freezing).
  • Hedgehogs have large deposits of brown fat in addition to white fat. The white fat, which can account for 1/3 of body weight just before hibernation, provides the constant energy supply to fuel metabolism during hibernation while brown fat is most important for heat generation during arousals from hibernation. 
  • If fat stores are insufficient then the hedgehog will not survive hibernation.
  • Elevated levels of serotonin and reduced levels of noradrenaline are thought to be involved in initiation and maintenance of hibernation. Hormone levels change seasonally, for example prolactin levels are elevated during hibernation while thyroxine levels are reduced. 

Normal temperature:

  • Normal body temperature for hedgehogs is within the range 35 +/- 2C. (B228.6.w6)
  • The majority of body temperature reports for the hedgehog within the literature are within the range 33.5 - 36.75C. (B228.6.w6)
  • Body temperature in a study of active hedgehogs (not in hibernation) in captivity was found to be 35.4C (+/- 0.5C). (B228.6.w6)
  • Circadian variation in body temperature has been reported with minimum values at midday and peak values at midnight (GMT) in Scotland. (B228.6.w6)
  • A diurnal rhythm of body temperature has been recorded in hedgehogs, with the summer body temperature peaking at about 36.75C at 0300 hrs (3 am) and dropping to about 34.75C in early afternoon (1500 hrs, 3 pm). In non-hibernating hedgehogs in winter slightly lower values were recorded: 35.5C and 33.5C respectively. (B258.w5)
  • Using intra-abdominal temperature-sensitive radio transmitters in captive hedgehogs exposed to natural environmental conditions in north-east Scotland, it was shown that hedgehogs have seasonal changes in body temperature and a circadian rhythm, closely correlated with photoperiod. The magnitude of the daily temperature cycle is reduced in summer. (J189.160.w1)
  • Variation in the records of body temperature in the literature may be due to its circadian cycle and the recording technique used e.g. rectal or oesophageal probe.(B228.6.w6)
  • Body temperatures in lactating females were shown to be significantly higher and less variable than those of pregnant and non-breeding individuals. (J206.82.w1)
  • Body temperature of unweaned hoglets is about 31.5-34.0C. (J180.26.w1)

Fat Deposits

  • Hedgehogs, as with other hibernating species, have two kinds of adipose tissue or fat deposits.
    • 'White fat' provides the constant supply of energy required to fuel low level metabolism during hibernation and tends to be located within subcutaneous layers and around the intestinal mesenteries. (B228.6.w6, B255.6.w6, B289.3.w3) White fat can account for as much as one third of total body weight at the beginning of hibernation. (B254.27.w27, B260.5.w5)
    • 'Brown fat' reserves are developed in species which hibernate and are used to generate heat to increase body temperature to normal levels during arousal. (B228.6.w6, B285.w1) Brown adipose tissue has a high density of mitochondrial organelles, small lipid globules to facilitate rapid utilisation and a rich blood supply to provide oxygen to fuel the heat-generating metabolic pathway. (B228.6.w6)
    • 'Brown fat' in hibernating animals has also been called the "hibernating gland". (B289.3.w3)
  • Brown adipose tissue, historically known as the 'hibernating gland' (B142, B228.6.w6, B255.6.w6, B260.5.w5), tends to be distributed in discrete lobes in the hedgehog with a 'vest-like arrangement' about the vertebral column, thorax, shoulders and the neck. (B228.6.w6, B255.6.w6, B260.5.w5)
    • The largest lobes are located in the armpit or axillary area extending into the neck in close proximity to essential structures including the "external jugular vein, the thyroid and thymus glands, and the neck musculature". (B228.6.w6)
    • Minor deposits of brown adipose tissue in the hedgehog are scattered around a number of organs including the "adrenals, autonomic ganglia, kidneys and suprailiac region". (B228.6.w6)
  • Brown adipose deposits are a characteristic, distinct orange/ brown colouration and become darker as they are used. The water content increases as metabolic water is produced. (B228.6.w6)
  • Thermogenesis from brown adipose tissue is under the control of the sympathetic autonomic system and adrenal hormones. (B228.6.w6)

In Hibernation:

  • The body temperature during hibernation may be 2-5C. (J9.168.w1)
  • Body temperature during hibernation at 5C was measured as 7.5C. (J194.25.w1)
  • Body temperature (measured using a subcutaneously implanted thermocouple) in induced hibernation at 5C and 10C found that at both temperatures the hedgehog's temperature was less than 1C higher than the surrounding ambient temperature. (J200.1.w1)
  • Body temperature (measured using a subcutaneously implanted thermocouple) in induced hibernation at 4.2C found that the hedgehog's temperature was less than 1C higher than the surrounding ambient temperature. (J201.82.w1)
  • The body temperature (measured using a subcutaneously implanted thermocouple) in hedgehogs in an ambient temperature of -5C was never below 2.5 +/- 0.2C for the interscapular area while the temperature recorded by thermocouples similarly implanted over the hind quarters sometimes fell below 0C. (J201.82.w1)
  • The optimum temperature for hibernation appears to be about 4C; energy consumption is increased if the temperature is much higher (e.g. 10C) or lower (e.g. -5C) than this. (B228.6.w6, J200.1.w1, J200.5.w1)
  • Generation of heat from brown adipose tissue can rapidly increase the body temperature of the hedgehog from the low levels of hibernation to normal temperature within the active season; increase of body temperature from 1-5o C during hibernation to normal values can occur within approximately three hours. (B228.6.w6)
  • In order to survive through hibernation, it is essential that hedgehogs develop sufficient white fat reserves to fuel many weeks and sufficient brown fat reserves for several periods of arousal. If fat stores are insufficient the hedgehog will enter hibernation and subsequently die. (B254.27.w27)
  • Behavioural thermogenesis can be used to supplement heat derived from brown adipose tissue at the onset of arousal from hibernation e.g. shivering. (B228.6.w6)
  • Hedgehogs break down their fat reserves in lipolysis to supply energy during hibernation. Carbohydrate metabolism is reduced to a minimal level, therefore levels of the key regulatory hormones, insulin and glucagon, are lowered, and gluconeogenesis and glycogenolytic activity is minimal. (B228.6.w6)
  • Use of fat reserves during hibernation leads to a significant reduction in hedgehog body weight over winter; values from European studies reveal total weight loss in the order of 25-40%.(B228.6.w6)
  • It has been estimated, based on recorded post-hibernation weights, that hedgehogs in Britain need to weigh at least 450 g if they are to survive a hibernation during which they lose 25% of their body weight. To survive a hibernation in which 40% weight loss occurred (as has been recorded in Finland under laboratory conditions), a starting body mass of 550 g would be required. As 8-10 weeks are required to attain a weight of more than 500 g it is unlikely that hedgehogs born after September in the UK would be able to gain enough weight to survive hibernation. (J46.203.w1)
  • Data from several studies suggests that weight loss during hibernation is approximately 0.2-0.3% of body weight each day or one gram loss per day as a 'rule of thumb'. (B228.6.w6)
  • The metabolic rate of hedgehogs is slowed to approximately 1 or 2% of normal values during hibernation. (B228.6.w6)
  • While daily torpor may reduce metabolism to about 30% of active metabolism, hibernation reduces metabolism to about 5% of the minimum rate for the non-torpid animal. (J193.68.w1)
  • Metabolic energy demand during hibernation increases with either increase or decrease of ambient temperature.
    • Lowered ambient temperatures require additional heat generation to prevent frostbite in the tissues. (B254.27.w27)
    • Raised ambient temperatures will passively increase the hedgehog body temperature and therefore increase metabolism and energy demand.
    • The rate of utilisation of fat reserves will therefore be increased by extremes of ambient temperature, reducing the possible length of the period of hibernation and potentially stimulating premature arousal. (B228.6.w6)
  • Factors affecting the total energy use during the period of hibernation include environmental temperature, frequency and duration of arousal. (B228.6.w6)
  • The metabolism of hedgehogs maintained in an ambient temperature of -5C was accelerated compared to that of the same animals maintained in an ambient temperature of +4.2C: the oxygen consumption was much higher (227.1 +/- 14.3 ml/kg/hour, compared to 10.4 +/- 0.53 ml/kg/hr). (J200.5.w1)
  • A study involving measurement of oxygen consumption by hedgehogs during hibernation, arousal and normal activity (normothermy) concluded that in conditions of low environmental temperatures a hedgehog would take 100 days to use fat stores if hibernating but less than one day to use up the same fat stores if remaining not in hibernation. (J194.25.w1)
  • Oxygen consumption over the total period of arousal was shown not to be significantly different from consumption over the same length of time in the awake hedgehog, although peak oxygen consumption was greater than normal oxygen consumption in the awake hedgehog. (J194.25.w1)
  • Weight loss during the total hibernation period is reduced if the hedgehog spends more of its time in deep hibernation and less of its time awake. (J200.1.w1)
  • A study showed that heart and liver glycogen levels are raised during hibernation, while blood glucose is lowered. (J205.S380.w8)
  • The pancreatic enzymes insulin and glucagon are both at very low levels during hibernation; this is related to the near-cessation of carbohydrate metabolism. (B228.6.w6, J205.S380.w8)
  • Protein metabolism is reduced during hibernation and protein catabolism for energy supply is negligible during this period. Blood urea levels do not increase significantly during hibernation.(B228.6.w6)

Endocrine Factors:

  • The hypothalamus and its control centres which regulate homeostasis remain active throughout hibernation. (B228.6.w6)
  • Evidence suggests that two major neurotransmitters are chiefly responsible for the control of hypothermia during hibernation. Elevated levels of serotonin (5-hydroxytryptamine) and reduced levels of noradrenaline are thought to lead to lowering of body temperature and maintenance of hibernation whilst the converse situation leads to heat generation and subsequent arousal from hibernation. (B228.6.w6)
  • Function of the endocrine system is typically seen to be depressed early in the hibernation period and to resume during the latter stages of hibernation for seasonal hibernators. However endocrine system activity may occur during periodic arousals which occur routinely during hibernation. (B228.6.w6)
  • The thyroid gland, which produces the hormone thyroxine, an important factor regulating the metabolic rate, has been shown to regress during autumn and the first period of hibernation whilst its activity recommences towards the end of hibernation. (B228.6.w6)
  • A study found that in June and July the mean adrenaline content of the adrenal glands of active adult (full-grown) male hedgehogs was 296 g/g and the nor-adrenaline content was 186 g/g; for non-pregnant females the values were 220 g/g and 90 g/g respectively, however the adrenals were larger than in the male, particularly the adrenal cortex. The mean weight of the adrenal glands was 70% higher for females than for males. (J201.27.w1)
  • Changes in hormone levels are seasonal and reflect the latitude at which the hedgehogs live. (J206.84.w1)
  • Melatonin levels peak between November and February with lowest concentrations summer to early autumn. Melatonin concentrations were significantly higher when daylight lasted less than 10 hours and fell proportionately as day length decreased. (J206.84.w1)
  • Prolactin levels were found to be significantly elevated during hibernation (compared to levels in summer). (J206.84.w1)
  • Levels of B-endorphin were found to be significantly lower in winter and higher March to September, during the period of greatest metabolic and reproductive activity. (J206.84.w1)
  • Thyroxine levels were found to be up to 12 times lower in winter than in summer. (J206.84.w1)
  • Urinary cortisol levels were significantly higher October/December than January/February. There were considerable differences between plasma and urinary values of males and females; there were also differences between day and night levels in males. (J206.84.w1)
  • During deep hibernation the level of noradrenaline was consistently very low while that of adrenaline was considerably higher than in summer. (J9.182.w1)

(B142, B228.6.w6, B255.6.w6, B254.27.w27, B258.w5, B260.5.w5, B285.w1, B289.3.w3, J9.168.w1, J9.182.w1, J46.203.w1, J180.26.w1, J193.68.w1, J194.25.w1, J200.1.w1, J200.5.w1, J201.27.w1, J201.82.w1, J205.S380.w8, J206.82.w1, J206.84.w1)

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Respiratory System (Respiration)

Source Information SUMMARY:
  • The respiratory rate of active hedgehogs is variable and may be 25 breaths per minute when resting, rising to 50 breaths per minute during exercise.
  • During hibernation respiratory rates are reduced with periods of apnoea (average about 56 minutes, sometimes as long as 150 minutes) followed by a period of a number (40-50) rapid breaths. In very cold conditions (ambient temperature below freezing) periods of apnoea are reduced or absent.
  • Oxygen consumption is greatly reduced during hibernation, at 5C to only 0.5% of normal resting levels. Oxygen consumption is higher at 10C and at -5C than at 4-5C (the optimum temperature for hibernation).

Normal respiration:

  • Respiratory rates for the hedgehog are highly variable. (B228.6.w6)
  • Average respiratory rates in resting hedgehogs during the active season are reported to be 25 breaths per minute, although values increase to approximately 50 breaths per minute at exercise. (B228.6.w6)
    • A normal respiratory rate for active (non-hibernating) hedgehogs during the daytime, while resting, has been recorded as 25 +/- 4 breaths per minute. (J201.82.w1)

In Hibernation:

  • Respiratory rates during hibernation are reduced to levels of 13 breaths per minute or less (B228.6.w6); approximately ten irregular breaths each minute. (B142, B260.5.w5); approximately nine breaths per minute with longer interruptions of several minutes. (B258.w5)
  • Periods of apnoea lasting about 10 minutes were noted in hedgehogs in induced hibernation (by exposure to low temperatures 5C or 10C in August. (J200.1.w1)
  • Hedgehogs in deep undisturbed hibernation showed periods of apnoea of about 56 minutes alternating with periods of breathing for about four minutes. The longest recorded period of apnoea lasted 150 minutes. About 40-50 inspirations occur during a period of respiration. (J201.82.w1)
  • Respiration in hedgehogs in an ambient temperature of -5C did not show periodic apnoea; at an ambient temperature of -1.5C periods of apnoea lasted only four minutes. (J201.82.w1)
  • Hedgehogs may exhibit periods of respiratory apnoea during deep hibernation (B254.27.w27) of variable length (average reported duration 56 minutes in one study, with a maximum of 150 minutes). This physiological adaptation is believed to act as a mechanism to reduce energy expenditure and insensible water losses associated with respiration. (B228.6.w6)
  • Hedgehogs have the ability for efficient anaerobic metabolism but rarely become significantly oxygen deficient during hibernation because of their cardio-vascular system adaptations. (B228.6.w6)
  • Oxygen consumption during hibernation at 5C is greatly reduced, to only 0.5% of normal resting oxygen consumption. (J194.25.w1)
  • The reduction in oxygen consumption is temperature-dependent with a greatest reduction in consumption seen at 5C than at 10C. (J194.25.w1)
  • Studies of blood gases during hibernation showed a higher PaO2 for hibernating hedgehogs versus non-hibernating controls. PaCO2 levels were higher in the hibernating than the non-hibernating animals and pH was lower. (J205.S380.w6)
  • Hedgehogs maintained in an ambient temperature of -5C showed a regular respiratory rhythm of 8-9 breaths per minute. (J200.5.w1)
  • The metabolism of hedgehogs maintained in an ambient temperature of -5C was accelerated compared to that of the same animals maintained in an ambient temperature of +4.2C: the oxygen consumption was about 22 times higher (227.1 +/- 14.3 ml/kg/hour, compared to 10.4 +/- 0.53 ml/kg/hr). (J200.5.w1)
  • Water losses through evaporation are minimised during hibernation by the slow respiratory rate and low body temperature of the hedgehog. (B228.6.w6)

(B142, B228.6.w6, B254.27.w27, B258.w5, B260.5.w5, J194.25.w1, J200.1.w1, J201.82.w1, J205.S380.w6)

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Circulatory System (Pulse / Heart Rate)

Source Information SUMMARY:
  • The heart rate of hedgehogs may be about 147 beats per minute (bpm) for a sleeping hedgehog and 200-280 bpm for an awake hedgehog.
  • In hibernation the rate may drop to 2-12 bpm. All components of the ECG are prolonged in hibernating hedgehogs.
  • A variety of changes occur prior to and during hibernation, for example splenic enlargement and decreases in the water content of muscle, liver and blood (but not of the brain, heart and kidneys)

Normal heart rate:

  • Hedgehog heart rates at normal body temperature during the active season when awake are reported to be between 200-280 beats per minute and when asleep 147 beats per minute. (B228.6.w6)
  • In one study heart rates recorded using ECG averaged 188 beats per minute for hedgehogs weighing 420-920 g . (J9.168.w1)
  • Hedgehog heart rates are highly variable and respond quickly to disturbance during the active season or hibernation. (B228.6.w6)

In Hibernation:

  • Heart rates during hibernation have been observed to vary with even minimal disturbance to enable recording techniques leading to elevation of the resting rate. Various studies have found that hedgehog heart rates at typical hibernating body temperature of 4C ranged between 2 to 12 beats per minute, to average 13.7 beats per minute and to fluctuate at around a rate of five beats per minute but with an increase to at least 10 beats per minute with the stimulus of even the slightest touch (and to 20-25 beats per minute when pre-implanted electrodes were connected up); measurements taken by palpation found rates of 25 beats per minute. (B228.6.w6)
    • In one study heart rates recorded using ECG were 188 beats per minute for hedgehogs weighing 420-920 g but decreased to 21 beats per minute for hibernating hedgehogs (bodyweight 420-770 g) at body temperature 6.2-7.7C. It was postulated that lowered body temperature, increased vagal tone, and probably also increased serum magnesium, decreased potassium and increased CO2 levels might be responsible for this change. (J9.168.w1)
    • A study comparing rates in hibernating hedgehogs to those in non-hibernating hedgehogs, using an electrocardiogram with standard leads I, II and III, found an average of 13.7 beats per minute (bpm) in the hibernating animals compared with 244 bpm in autumn, 276.9 bpm in spring and 256.5 bpm in summer; the differences between seasons (other than during hibernation) were not significant. (J205.S380.w2, J205.S380.w4)
    • For hibernating hedgehogs maintained at an ambient temperature of -5C the heart rate was regularly 21-24 beats per minute, compared with 4-7 beats per minute for animals held in an ambient temperature of +4.2C. (J200.5.w1)
    • Active (non-hibernating) hedgehogs show heart rates of about 185-210 beats per minute compared to normal values for hibernating individuals of 2-12 beats per minute for individuals hibernating in an ambient temperature of 4.2C. (J201.82.w1)
    • Heart rates during hibernation decrease to less than twenty beats per minute (B142, B260.5.w5); approximately 10 beats per minute. (B285.w1)
    • In hedgehogs in an ambient temperature of -5C the heart rate was recorded at 19 beats per minute dropping to 13-17 beats per minute at -1.5C and about eight beats per minute at 4.5C. (J201.82.w1)
    • The slowest heart rates for hibernating hedgehogs reach 2-3 beats per minute; the longest period between beats may reach 276 seconds. (J201.82.w1)
    • Heart rates of undisturbed hedgehogs maintained at a constant temperature are uneven; the respiration pattern affects the recorded heart rate. (J201.82.w1)
    • It has been suggested that a heart rate of 20 beats per minute or higher indicates that a hedgehog is not in deep, undisturbed hibernation. (J201.82.w1)
  • Physiological adaptations permit the heart to continue to pump without fibrillation at low body temperature as would be expected in other mammal species. (B260.5.w5)
  • Hedgehogs, as with other hibernators, have evolved several adaptations of their cardiovascular physiology to enable function at reduced body temperature. These include specialised metabolism with high glycogen stores in cardiac tissue, electrocardiographic changes and membrane permeability optimisation. (B228.6.w6)
    • All components of the ECG are prolonged in hibernating hedgehogs, the S-T segment being short or absent. (J205.S380.w4, B228.6.w6)
  • During arousal blood circulation is concentrated anterior to the diaphragm; in animals which are disturbed circulation increases first in the heart and the brown fat; circulation is also increased in the thyroid and lungs. Circulation to the kidneys does not increase until the hedgehog is nearly normothermic. (J201.110.w1)
  • In autumn prior to hibernation the water content of the muscle, liver and blood of hedgehogs decreases significantly while that of the brain, heart and kidneys does not. (J201.92.w1)
  • The spleen enlarges in the hibernation season, with the enlargement persisting during hibernation. (J201.110.w1)

(B142, B228.6.w6, B260.5.w5, B285.w1, J9.168.w1, J200.5.w1, J201.110.w1, J205.S380.w2, J205.S380.w4)

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Gastrointestinal System (Faeces and Gut Motility)

Source Information SUMMARY:
  • Normal hedgehog droppings are cylindrical, about 2-3 cm long and black, dark grey or dark green, usually with visible bits of insect parts on them. Faeces from juveniles are softer than those of adults and greyish green in colour.
  • Gastro-intestinal: Gut transit time is short; most ingesta is passed within 12-16 hours of ingestion. It is thought that only negligible bacterial fermentation occurs in digestion. During hibernation there are changes including involution of mucosal secretory glands.

Faeces Production

  • Faeces are dark grey or black in colour with a characteristic coating of glossy fragments of beetle exoskeleton. (B142, B228.3.w3, B260.1.w1)
  • Normal faeces just before, and sometimes just after, hibernation may be dark green. (B337.3.w3, V.w56)
  • Droppings are typically 2-3 cm (0.75-1.25 inches) long and 1 cm (0.5 inch) wide. (B260.1.w1); 3-4 cm long by 1 cm diameter (B269); 1.5 - 5 cm long (B268)
  • Cylindrical, 1-2 inches long, the thickness of a pencil, and black or dark green, often with visible fragments of beetles or millipedes. (J207.2.w1)
  • Faeces have a variable cylindrical, profile with tapered ends. (B142, B228.3.w3); faeces are pointed at one end. (B269)
  • Firm and sausage-shaped, usually brown or black in adults. (B291.12.w12)
  • Dropping size ranges from 15-50 mm long, approximately 10 mm in diameter. (B142, B228.3.w3)
  • Hedgehog faeces are typically a dark colour with a 'knobbly' profile and contain undigested invertebrate food such as remnants of beetles. (B261)
  • Faecal pellets have a granular appearance.( B262.3.w3)
  • Faeces contain in large part the hard parts of insects such as legs, heads, wing-cases and antennae. (B255.3.w3)
  • Droppings are deposited singly and not in batches. (B262.3.w3)
  • Faeces are usually deposited singly, sometimes in pairs and rarely in larger numbers. (B228.3.w3)
  • Whilst some studies have described non-random distribution of faeces within hedgehog habitat, territorial scent marking has not been shown to occur in hedgehogs. Random distribution of single hedgehog droppings is commonly observed in the field. (B228.2.w2, B254.18.w18)
  • The consistency of hedgehog faeces varies with diet but they are usually quite dry. (B228.3.w3)
  • Droppings do not have a particularly strong odour. (B268)
  • Normal faeces of juveniles are softer than those of adults and are greyish green. (B291.12.w12)

(B142, B228.2.w2, B228.3.w3, B254.18.w18, B255.3.w3, B260.1.w1, B261, B262.3.w3, B268, B269, B291.12.w12, B337.3.w3, V.w56)

Gastro-intestinal system:

  • Gut transit in the hedgehog is rapid with the majority of ingesta passed within 12-16 hours. (B228.3.w3)
  • Although volatile fatty acids and lactic acid have been detected within the large intestine of the hedgehog, it is not believed that a significant amount of bacterial fermentation occurs in digestion. (B228.3.w3)
  • Evidence to date does not suggest that hedgehog's digest vegetable matter within their diet. (B228.3.w3)

In Hibernation:

  • Changes in the gastro-intestinal tract during hibernation include involution of the mucosal secretory glands although bile secretion and activity in the exocrine component of the pancreas has been shown to continue. (B228.6.w6)
  • In autumn prior to hibernation the water content of the muscle, liver and blood of hedgehogs decreases significantly while that of the brain, heart and kidneys does not. During hibernation the water content of the liver increases. (J201.92.w1)

(B228.3.w3, B228.6.w6, B254.33.w33, J201.92.w1, J201.110.w1)

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(Urinary System) Urine

Source Information SUMMARY: During hibernation urine production is greatly decreased. Small volumes of urine may be produced and voided during the periods of arousal.

In Hibernation:

  • Kidney function is reduced during hibernation which is possible since levels of metabolic waste production are also reduced. (B228.6.w6)
  • Metabolic water is produced through the breakdown of fat energy reserves during hibernation therefore small volumes of urine are produced and voided during brief periods of arousal. (B228.6.w6)
  • Bladder urine electrolyte concentrations were shown to be markedly lower in hibernating hedgehogs than in awake hedgehogs. Osmolarity was 1.1 Osm/l for hibernating hedgehogs versus 1.7 Osm/l for awake hedgehogs, urea concentrations were 650 mM/l and 900 mM/l respectively. (J205.83.w1)
  • Hibernating hedgehogs have been found to have hyperosmotic (1.1 Osm/l) urine in the bladder (compared to the plasma); this is probably produced mainly or only during the intermittent arousal periods, since the renal counter current multiplier system is practically inoperative during deep hibernation. (J205.83.w1)

(B228.6.w6, J205.83.w1)

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Chromosomes

Source Information SUMMARY: 2n = 48 Chromosomes.

(B142, B228.1.w1, B285.w1)

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Musculo-Skeletal System

Source Information SUMMARY: Hedgehogs can roll into a tight ball with spines bristling in all directions as part of their defensive behaviours.

Mechanism of rolling into a ball:

  • Complex cutaneous musculature permits spine erection and allows the hedgehog to roll into a tight defensive ball. (B262.2.w2)
  • The fronto-dorsalis (fronto-orbicularis or preorbitalis dorsalis) muscle, which extends over the hedgehog forehead, is used to draw the spiny skin of the head down to protect the face. The hedgehog is still able to keep its eyes and ears open whilst this muscle is contracted. (B262.2.w2)
  • The caudo-dorsalis and caudo-abdominalis muscles, located over the base of the back, function to retract the rump and tail respectively when the hedgehog curls into a ball. (B228.2.w2)
  • The panniculus carnosus muscle is developed into a thick circular band of orbicularis muscle around its margins. Co-ordinated action of a number of muscles acts to pull the spined skin over the head, limbs and tail in a similar fashion to a 'hood'. Contraction of the orbicularis muscle then acts to tighten the opening to the undercarriage. (B228.2.w2)
  • When a hedgehog rolls into a tight ball, stretching of the muscles responsible for elevating the spines occurs with them automatically being erected; therefore the tighter the ball, the more prominent the spines. (B285.w1)
  • Contraction of the panniculus carnosus muscle at a focal point of physical contact will occur, temporarily increasing the density of spines in the area for additional protection. (B262.2.w2)

(B228.2.w2, B262.2.w2, B285.w1)

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Special Senses and Vocalisations:

Source Information The most important senses to hedgehogs are hearing and olfaction. Their hearing is acute, particularly at high frequencies. Their sense of smell is also highly developed; both are used in detecting prey. Vision is relatively unimportant although hedgehogs are far from blind and even appear to have limited colour vision in good light. Normal behaviour has been recorded in an almost blind radio-tracked hedgehog, although it did bump into objects. Hedgehogs appear to have a well developed sense of taste. The vomeronasal organ (Jacobson's organ) is well developed and functional. They also possess a few long tactile sensory hairs on the snout. They do not use echolocation.

Hedgehogs produce a range of sounds including squeaking and whistling by hoglets, loud snuffling while foraging, puffing snorts during courtship and quarrels, loud chattering sounds (probably made by the teeth) and a high pitched scream in severe pain or distress.

Vision:

  • Vision is a "relatively unimportant" special sense for the hedgehog. (B262.9.w9)
  • Vision is not likely to be a particularly valuable special sense for hedgehogs since they inhabit areas with dense ground vegetation which may obscure lines of sight and are nocturnally active. (B228.2.w2)
  • Hedgehog vision is believed to be largely monochromatic. (B228.2.w2, B285.w1)
  • The photoreceptors in the hedgehog retina consist of rods only (for monochromatic vision), cones (for colour vision) are absent. (B228.2.w2)
  • Coniform (cone-type) nuclei have been reported to be present in some (3.75%) of the rods within the hedgehog retina. (B228.2.w2, B255.5.w5)
  • Hedgehogs cannot see in full colour during the night but are able to differentiate some colours with increased light levels during the day. (B254.10.w10)
    • Hedgehogs have been reported experimentally to have some limited ability to discriminate between certain colours in good light. (B228.2.w2)
    • In experiments requiring the opening of certain sliding doors to reach food, hedgehogs were shown to be able to distinguish between black and white, different shades of grey, blue and yellow, yellow and grey and yellow versus "all other colours". (B258.w8)
  • Observation of hedgehogs suggest that their visual acuity is reasonable. (B228.2.w2)
    • Experimentally, hedgehogs were shown to be able to distinguish between different shapes. (B258.w8)
  • Hedgehogs are believed to recognise habitat landmarks as distinctive silhouetted shapes. (B254.10.w10)
  • It has been suggested that injury to the eyes occurs not infrequently in wild hedgehogs and yet these individuals "can survive well even though partially blind". (B262.9.w9)
    • Radio-tracking study of an almost blind male hedgehog identified that whilst the individual did bump into objects, it was able to lead a normal life including travelling long distances at rapid speed and performing normal courtship behaviour. (B254.10.w10)

Touch/ Tactile

  • Hedgehogs do possess a few long sensory tactile hairs on their snout.(B254.10.w10)

Olfaction:

  • Hedgehogs have a highly developed sense of smell which they use to find food, for individual recognition, to follow scent trails and for detection of danger. (B142, B228.2.w2, B254.10.w10, B258.w8, B262.9.w9, B285.w1, B291.12.w12)
  • Hedgehogs have a functional vomeronasal organ. (B291.12.w12)
  • Hedgehogs explore and investigate their habitat when foraging, noisily sniffing ground cover and using their sense of smell to help detect hidden prey. (B228.2.w2)
  • "Odour cues are important in many hedgehog activities, including finding food, detecting potential predators, orientation and place recognition, sexual behaviour, maternal behaviour and other interactions." (B228.2.w2)
  • Experimental work in the 1940's was performed on an anaesthetised hedgehog to explore its sensitivity to olfactory stimuli. Electrodes were implanted into the hedgehog's skull and were used to detect alterations in electrical potential in response to a variety of olfactory cues. The results of this work support the conclusion that olfactory acuity in the hedgehog is acute. (B228.2.w2, B255.5.w5)
  • Observational trials performed on captive hedgehogs investigating their sense of smell revealed that " hedgehogs could detect crushed beetles (cockchafers and carabids) at a range of up to 1 m (41% success), a dog at up to 11 m (42% success) and mice were reliably detected at 5 m." The results suggested that the hedgehogs were able to rapidly find food items with a similar level of proficiency to a dog. (B228.2.w2)
  • Hedgehogs are able to detect food through their sense of smell, even at a depth of 3 cm below the surface of soil. (B254.10.w10)
  • Contamination of regular food items with strong tasting salt, sour or bitter substances leads hedgehogs to reject the food source. However some foodstuffs supplemented with potent smelling and caustic substances were preferentially taken. (B228.2.w2)
  • The olfactory lobes of the hedgehog brain are particularly well developed, reflecting the importance of the sense of smell in this species. (B228.2.w2)
  • The vomeronasal organ (or Jacobson's organ) is well developed in the hedgehog, consisting of paired blind ending diverticulae which communicate through ducts to both the mouth and nasal chambers. (B228.2.w2) Whilst function of this organ is associated with sexual activity and the characteristic 'flehmen' response of ungulates and many carnivores, its role or function in the hedgehog remains unclear. However, the vomeronasal organ has been observed to be involved with self-anointing behaviour. (B228.2.w2)
  • Knowledge of the olfactory cues used for communication and interaction between hedgehogs is limited to date. (B228.2.w2)
  • Production of olfactory cues from a variety of body products, excretions and secretions is possible although little data is available on the topic. These include urine and faeces, vaginal glands, accessory sex glands, a proctodeal gland and eccrine sweat glands. (B228.2.w2)
  • Scent-marking has been described during courtship behaviour where secretions from the penis, believed to originate from the accessory sex glands, were used to scent the ground. (B228.2.w2)
  • A lobulated proctodeal gland (sebaceous) is present within the entrance to the anal opening (6-7 mm long by 4.5 mm wide). The gland's function may involve adding odour cues to faeces, although behaviour patterns associated with anal scent gland marking have not been observed in the hedgehog. (B228.2.w2)
  • Self-anointing behaviour in hedgehogs is usually stimulated by contact with an odour cue. The hedgehog produces large quantities of frothy saliva which is spread, often in mixture with the stimulus material, over the animal's body. Whilst the reason for self-anointing behaviour remains ill understood, it is related to activity of the vomeronasal organ and significant olfactory stimulation. (B228.2.w2)
  • Olfactory cues represent a useful form of communication for the hedgehog since it is a nocturnal and non-social species. (B228.2.w2)
  • Whilst some studies have described non-random distribution of faeces within hedgehog habitat, territorial scent marking has not been shown to occur in hedgehogs. Random distribution of single hedgehog droppings is commonly observed in the field. (B228.2.w2)
  • Research into potential scent cues is needed to further investigate olfactory communication between hedgehogs. (B228.2.w2)
  • Navigation is likely to rely principally on auditory and olfactory cues, although visual cues have also been suggested to play a role. (B228.2.w2)
  • Hedgehogs have been shown to avoid areas with badger scent. (B285.w1)

Hearing:

  • The auditory system of hedgehogs is adapted for the detection of high-frequency sound. (B228.2.w2, B285.w1)
  • Hedgehogs use their acute sense of hearing to pinpoint and locate invertebrate prey hidden within ground substrate.(B228.2.w2, B254.10.w10, B262.9.w9)
  • Erinaceus europaeus has been reported to hear the sound of a dung beetle moving five metres away.(B228.2.w2)
  • "High-frequency sound is relatively easy to locate because of its short wavelength in relation to ear separation and pinna sizes." (B228.2.w2)
  • Hedgehogs generally flinch and curl up in response to chirping noises due to the ultra-sonic components of the sound. (B291.12.w12)
  • Experimental work monitoring the 'flinch reflex' in East European hedgehog - Erinaceus concolor individuals in response to auditory stimuli noted that the reflex was abolished when the high-frequency, ultra-sonic component of a sound was removed. (B228.2.w2)
  • Hemiechinus auritus, a long-eared hedgehog species, has been shown to respond to frequencies as high as 45 kHz. (B228.2.w2, B285.w1)
  • As their names suggest, long-eared hedgehogs (Hemiechinus and Paraechinus genera) have larger ears and auditory bullae than Erinaceus species (Erinaceus - (Genus)). This is believed to be associated with more sensitive hearing in the former group although this has not been proven to date.(B228.2.w2)
  • Navigation is likely to rely principally on olfactory and auditory cues, although visual cues have also been suggested to play a role. (B228.2.w2)
  • Hedgehogs seem particularly sensitive to "abrupt sounds" e.g. clicks. (B254.10.w10)

Taste:

  • Food preference tests have demonstrated the hedgehog's ability to taste and discriminate between food sources. However, the hedgehog diet is fairly catholic and includes several species which are unpalatable to other predators e.g. millipedes. (B254.10.w10)
  • Captive tame hedgehogs, in contrast, may become accustomed to an artificial diet and refuse alternate less desirable food stuffs when offered. (B254.10.w10)
  • It has been noted that hedgehogs show "marked and highly individual preferences for certain foods with a characteristic flavour"; this is taken to indicate a well developed sense of taste. (B258.w8)

Temperature:

  • Hedgehogs are very sensitive to temperature. In a cold room they will sleep in a warm place such as near a radiator or stove. Presented with a temperature gradient (in a cage with a metal floor heated at one end, cold at the other), hedgehogs will settle at a preferred temperature characteristic for the species and population. (B258.w8)

Other senses:

  • Current evidence does not support the suggestion that hedgehogs use echolocation.(B228.2.w2)
  • Mechanisms for navigation involving detection of magnetic fields and orientation to the moon and stars have been hypothesised. (B228.2.w2)

(B228.2.w2, B254.10.w10, B255.5.w5, B258.w8, B262.9.w9, B285.w1)

Vocalisations:

  • Hedgehogs are usually silent. (B142)
  • The vocal repertoire of hedgehogs is varied and includes "audible high-pitched twittering sounds", "shrill piping whistles" "purely ultrasonic clicks" from neonates (often used to signal alarm when offspring become separated from the sow); "clucking", "the quack" (uncommon sound issued when a hedgehog is "bothered" or in mild pain) and a piercing high-pitched scream (rare distress call). (B228.2.w2)
  • "Snorting, spitting, puffing and huffing" noises are made via exhalation through the nostrils and signal aggression or a warning. (B228.2.w2)
  • Squeaking by hoglets jostling to suckle. (B258.w8)
  • Whistle by hoglets isolated or left behind by the sow. (B258.w8)
  • Loud sniffling while foraging. (B258.w8)
  • "Puffing snort" while quarrelling or courting. (B258.w8)
  • "Loud shrill chatter" made in situations of pain, fear or anger. (B258.w8)
  • Loud scream in extreme pain and distress. (B258.w8)
  • A high-pitched, shrill, almost metallic whistle and a squeaky quack are both used by hoglets. (B255.2.w2)
  • Calls from mother to baby, a bird-like whistle, have also been observed. (B255.2.w2)
  • A clicking or ticking sound made by stationary hedgehogs is probably made by the teeth. (B255.2.w2)
  • The scream of distress is extremely loud. (B255.2.w2)
  • Loud, "churring" sounds, considered to be "defiant and aggressive" have been heard in a hedgehog encountering a dog. (B255.2.w2)
  • Loud sniffing and snoring noises are normal, increasing to hissing or puffing sounds in excited individuals. A loud chattering noise may be made by angry or frightened hedgehogs and a shrill scream by severely distressed individuals. (B291.12.w12)
  • Hedgehogs rarely produce a piercing high-pitched scream/squeal in situations of stress (e.g. apprehension on handling (B254.10.w10), when alarmed (B261, B262.9.w9) or in pain or distress. (B142, V.w26))

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Authors & Referees

Authors Becki Lawson (V.w26); Debra Bourne (V.w5)
Referee Suzanne I. Boardman (V.w6); Nigel Reeve (V.w57)

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