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DETAILED PHYSIOLOGY - Editorial Comment

Editorial Comment

(Editorial Overview Text Replicated on Overall Species page - Ursus arctos - Brown bear)

METABOLISM (TEMPERATURE): The normal rectal temperature of adult bears is 36.5 - 38.5 C (97.7 - 101.3 F)

RESPIRATORY SYSTEM (RESPIRATION): The normal respiratory rate is 15 - 30 breaths per minute. During hibernation this may decrease to as low as one breath per minute.

CIRCULATORY SYSTEM (PULSE/HEART RATE): The normal heart rate in active brown bears is 40 - 50 bpm, or higher in cubs. During hibernation it decreases to about 8 - 10 bpm. 

HAEMATOLOGY / BIOCHEMISTRY: Values are similar to those of the domestic dog.

GASTROINTESTINAL SYSTEM (FAECES AND GUT MOTILITY): Scats (faeces) are usually cylindrical, but may be rounded or massed. They may be more than 50 mm (2 in) wide. Animal hair, husks or vegetable fibres may be visible. Food passes through the short gastro-intestinal system quickly.

URINARY SYSTEM (URINE): --

CHROMOSOMES: 2n = 74 Chromosomes.

MUSCULO-SKELETAL SYSTEM: --

SPECIAL SENSES AND VOCALISATIONS: Brown bears have quite good vision, but better hearing and a superb sense of smell. All these senses are used in communication. Vocalisations include distress calls from both adults in pain and from hurt, hungry, separated or cold cubs, huffs and snorts of apprehension, growls and roars in aggression and chuffing as a close contact call.

(References are available in detailed literature reports below)

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Metabolism (Temperature)

Source Information

SUMMARY: The normal rectal temperature of adult bears is 36.5 - 38.5 C (97.7 - 101.3 F).
  • The normal rectal temperature of adult bears is 37.5 - 38.3 C (99.6 - 101.0 F). (B64.26.w5)
  • The normal rectal temperature of bears in 37.5-38.0 C. (B214.3.4.w16)
  • Normal about 38C (100F). In hibernation, reduced to about 34C (93F). (B285)
  • Body temperature decreases only slightly during hibernation. (B147)
  • Normal active temperature about 36.5 - 38.5 C. (D243)
  • Body temperature of two hand-reared cubs was 37 - 37.5 C (98.6 - 99 F). (J23.9.w4)
  • The fur of brown bears has been shown to have excellent insulating properties. (B399.3.w3)
  • The core body temperature of brown bears was measured as 37.0-37.5 C; during hibernation, it dropped 4-5 C below normal. The lowest values measured were 33.1-33.3 C; this temperature was reached several times in midwinter. (J400.109.w1)
  • During hibernation, body temperature is a few degrees below normal. (B406.36.w36)
  • Normal body temperature is 36.5 - 38.5 C in active bears, and drops 4-5 degrees during hibernation. (B490.26.w26, D284.w5)
  • While bears are in the den, their metabolic rate is only 51 kcal/kg0.75/day, i.e. about 68-73% of the usual basal metabolic rate for active mammals. (B490.26.w26)

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Respiratory System (Respiration)

Source Information

SUMMARY: The normal respiratory rate is 15 - 30 breaths per minute. During hibernation this may decrease to as low as one breath per minute.

Normal respiration: 

  • The normal respiratory rate of bears is 15 - 30 breaths per minute (the higher rates have been recorded in hot weather). (B64.26.w5)

During hibernation

  • The respiratory rate decreases markedly during hibernation. (B147)
  • During hibernation the respiratory rate may be as low as one breath per minute. (B406.36.w36)
  • Oxygen consumption during hibernation is reduced by as much as 50%. (D284.w5)

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Circulatory System (Pulse / Heart Rate)

Source Information

SUMMARY: The normal heart rate in active brown bears is 40 - 50 bpm, or higher in cubs. During hibernation it decreases to about 8 - 10 bpm. 
  • The normal heart rate of bears is 60 - 90 beats per minute (the higher rates are found in cubs). (B64.26.w5)
  • In summer 40-50 bpm. (D243)
  • The heart rate is 40-50 bpm (resting rate), reduced to 8-12 bpm during hibernation. (B490.26.w26, D284.w5)

During hibernation

  • During winter dormancy, 8-10 bpm. (D243)
  • The heart rate decreases markedly during hibernation. (B147)
  • During hibernation the heart rate may be as low as 10 beats per minute. (B406.36.w36)

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Haematology / Biochemistry

Source Information

SUMMARY: 
  • Values are similar to those of the domestic dog.

General: 

  • Values for haematology and biochemistry are similar to those of the domestic dog. (B336.51.w51)

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Gastrointestinal System (Faeces and Gut Motility)

Source Information

SUMMARY:
  • Scats (faeces) are usually cylindrical, but may be rounded or massed. They may be more than 50 mm (2 in) wide. Animal hair, husks or vegetable fibres may be visible. Food passes through the short gastro-intestinal system quickly.

Faeces Production:

  • Usually scats (faeces) are cylindrical; they may be rounded, or massed in areas where mainly vegetable food is eaten. They can be more than 50 mm (2 ins) wide, and animal hair, husks or vegetable fibres may be visible. (B180.w3)
  • A study found that the mean diameter of scats from brown bears (excluding those from cubs less than 20 months old) was 4.5 +/- 0.85 cm, with 58% of 104 faeces measuring < 5.0 cm diameter. Additionally, 43 scats were formless. Hairs from the bears (from grooming) were found in scats. (J59.9.w1)

Gastro-intestinal system:

  • Food traverses the relatively short GIT quickly and bears have a high food consumption rate. (B406.36.w36)
  • High-calorie, highly digestible foods are essential in the brown bear's diet. Being both monogastric and with a small or absent caecum, they cannot efficiently digest fibre and cannot significantly increase their fat reserves on a foliage-only diet. (B490.26.w26)
  • Meat passes through the GIT in about 13 hours, clover in about seven hours. (B490.26.w26)

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(Urinary System) Urine

Source Information

SUMMARY: --

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Chromosomes

Source Information

SUMMARY: 2n = 74 Chromosomes.
  • 2n = 74. (D243)
  • The 72 autosomes include 60 acrocentric, 12 metacentric or submetacentric. The X chromosome is large and metacentric, the Y chromosome small and acrocentric. (D243)

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Musculo-Skeletal System

Source Information

SUMMARY: --
  • --

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Special Senses and Vocalisations:

Source Information

SUMMARY: Brown bears have quite good vision, but better hearing and a superb sense of smell. All these senses are used in communication. Vocalisations include distress calls from both adults in pain and from hurt, hungry, separated or cold cubs, huffs and snorts of apprehension, growls and roars in aggression and chuffing as a close contact call.

Vision:

  • The eyesight of brown bears is relatively poor. (B147, B422.w14)
  • Eyesight is quite good. (B425)
  • The eyesight is good. (B406.36.w36)
  • Grizzly bears have been observed to see other bears or humans at distances as great as 1-2 km. (B490.26.w26)
  • At close range, body posture is important in communication. (D243)

Touch/ Tactile

  • --

Olfaction:

  • Bears have an excellent sense of smell. (B424)
  • Brown bears have an excellent sense of smell. (B147, B422.w14)
  • Excellent sense of smell. (B425)
  • Brown bears have a superb sense of smell. (B406.36.w36)
  • This is the most acute sense of brown bears. (B490.26.w26)
  • This is the most developed sense, and of major importance in locating hidden food items. (D284.w3)

Hearing:

  • Brown bears have excellent hearing. (B147)
    • On hearing a slight noise, a bear will raise its head and move the ears rapidly to locate the noise. (B422.w14)
  • Brown bears have excellent hearing. (B406.36.w36)
  • Hearing is good. (D284.w3)

Taste:

  • --

Temperature:

  • --

Other senses:

  • --

Vocalisations:

  • Sight, sound and particularly smell are used for communication. (D243)
  • Posture:
    • Body posture indicates ranking at close range: dominant individuals show a frontal orientation and approach, with outstretched neck, canines visible and ears back, while subordinates show a lateral orientation, with the head held low or turned away from the other bear, and may sit, lie down or back away. (D243)
  • Vocalisation:
    • Adults in pain may make distress calls. (D243)
    • Hungry, cold, hurt or separated neonates may make distress calls. (D243)
    • Individuals which are apprehensive may huff and snort. (D243)
    • Threatening animals growl and roar. (D243)
    • Adults and juveniles use "chuffing" ("a series of brief low-intensity sounds caused by a forceful exhalatory sound combined with a popping noise produced by movement of lips and cheeks" as a close-contact call for greeting, coaxing and appeasement. This is used during courtship and mating, also between female and cubs. (D243)
    • Cubs which are anxious (e.g. having lost sight of their mother) will emit a loud bawl; the female replies with a low "whoof" to orient the cub. (D283.w6)
  • Visual and olfactory:
    • Bears mark trees by biting, clawing and striping the bark. This indicates territory and sexual condition; marked trees are also used for grooming. (D243)
    • Bears mark trails by rolling on the ground, urinating and defecating. (D243)

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Authors & Referees

Authors

Dr Debra Bourne MA VetMB PhD MRCVS (V.w5)

Referee

Djuro Huber (V.w101), Chuck Schwartz (V.w105)

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