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< > DETAILED PHYSIOLOGY NOTES with literature reports for the American black bear - Ursus americanus: Use sub-contents list below, or simply scroll down the page to view findings.

DETAILED PHYSIOLOGY - Editorial Comment

Editorial Comment

(Editorial Overview Text Replicated on Overall Species page - Ursus americanus - American black bear)

METABOLISM (TEMPERATURE): The normal rectal temperature of adult bears is 37.5 - 38.3 C (99.6 - 101.0 F); in hibernating bears it falls to 31 - 34 C.

RESPIRATORY SYSTEM (RESPIRATION): The normal respiratory rate of bears is 15 - 30 breaths per minute (the higher rates have been recorded in hot weather); it is slower during hibernation. The normal respiratory rate of bears is 15 - 30 breaths per minute (the higher rates have been recorded in hot weather); it is slower during hibernation. Much faster respiration can be seen in bears resting in hot weather, e.g. 130 - 140 in cubs in summer.

CIRCULATORY SYSTEM (PULSE/HEART RATE): The normal heart rate of bears is 60 - 90 beats per minute (the higher rates are found in cubs).

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

GASTROINTESTINAL SYSTEM (FAECES AND GUT MOTILITY): Faeces (scats) are roughly cylindrical, sometimes coiled, usually dark brown, and may contain visible seeds, grasses, insect parts, animal hair, nut shells or root fibres; they may be black and liquid if bears are feeding on berries. Food passage time is short.

URINARY SYSTEM (URINE): Urine specific gravity has been measured as 1.025.

CHROMOSOMES: 2n = 74 Chromosomes.

MUSCULO-SKELETAL SYSTEM: --

SPECIAL SENSES AND VOCALISATIONS:

  • The American black bear's eyesight is poorer than that of humans, but they do have colour vision and at close range they have detailed vision and feed partially by sight. Distance vision may not be sufficient to allow black bears to stalk distant prey.
  • The sense of smell is excellent; they may smell carrion at a distance of more than a mile (1.6 km). Scent is the main method used by a female bear to recognise her offspring.
  • These bears have quite good hearing.
  • There are a variety of vocalisations, including a startled "woof", contented purrs of cubs, shrill howls or squalls of uncomfortable or frightened cubs and an "uh-uh" grunt by females calling her cubs to her.

(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 37.5 - 38.3 C (99.6 - 101.0 F); in hibernating bears it falls to 31 - 34 C.
  • 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)
  • 38 C in active bears. (B147)
  • In hibernating bears, 31 - 34 C. (B147)
  • In captive bears in Virginia, USA, mean rectal temperature was 38.0 C in autumn (fall) and 36.8 C in winter during hibernation (108 measurements, from six bears). (J1.25.w6)
  • Body temperatures in hibernating bears [species not specified] have been measured as 31 C, 33 C and 37.9 C. (P72.2.w1)
  • Body temperatures in hibernating bears have been measured as 31.2-36 C. (J345.10.w2)
  • During hibernation, metabolism averages 68% of predicted basal metabolic rate and may reach as low as 33% of basal metabolisms. (J345.10.w2)
  • For four bears held at an experimental station in northern Michigan, July body temperatures under anaesthesia averaged 98.6 C, but in February two bears had body temperatures averaging 95.3 C. (J332.42.w2)

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Respiratory System (Respiration)

Source Information

SUMMARY: The normal respiratory rate of bears is 15 - 30 breaths per minute (the higher rates have been recorded in hot weather); it is slower during hibernation. Much faster respiration can be seen in bears resting in hot weather, e.g. 130 - 140 in cubs in summer.

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)
  • Respiration is slower during hibernation. (B147)
  • A respiratory rate of 130-140 was seen in bear cubs resting in hot weather. (J345.2.w1)

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Circulatory System (Pulse / Heart Rate)

Source Information

SUMMARY: The normal heart rate of bears is 60 - 90 beats per minute (the higher rates are found in cubs).
  • The normal heart rate of bears is 60 - 90 beats per minute (the higher rates are found in cubs). (B64.26.w5)
  • In summer, the sleeping heart rate is usually above 40 beats per minute. During winter hibernation, this declines gradually over several weeks to reach 8-10 bpm. (P72.2.w1)
  • Four bears under pentobarbital sodium anaesthesia (following initial immobilisation with succinyl choline) had pulse rates of 118 0 176 bpm (mean 138 bpm), in July. Under the same regime in February, two had pulse rates of 144 and 96. (J332.42.w2)
  • On ECG, the pattern of hibernating bears shows a short Q-T segment. (P72.2.w1)

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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:
  • Faeces (scats) are roughly cylindrical, sometimes coiled, usually dark brown, and may contain visible seeds, grasses, insect parts, animal hair, nut shells or root fibres; they may be black and liquid if bears are feeding on berries. Food passage time is short.

Faeces Production:

  • Faeces (scats) are roughly cylindrical, sometimes coiled, usually dark brown, and may contain visible seeds, grasses, insect parts, animal hair, nut shells or root fibres. (B180)
    • When bears have been feeding heavily on berries, faeces may be black and liquid. (B180)

Gastro-intestinal system:

  • Food passage times are short. Food is ground in the muscular pylorus, and the stomach is highly acid (pH less than 3.5), assisting in digestion of protein and sugars, as well as breakdown of hemicellulose. The GIT appears adapted to digestion of fruit, nuts, insects and succulent vegetation, not for mature, non-succulent vegetation. (D248.w9)

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(Urinary System) Urine

Source Information

SUMMARY: Urine specific gravity has been measured as 1.025.
  • Specific gravity (four cubs, 9 - 10 months of age, held for 1 - 3 months) 1.025. (J460.19.w1)

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Chromosomes

Source Information

SUMMARY: 2n = 74 Chromosomes.
  • 2n = 74. (B399.9.w9)
  • 2n = 74. There are 64 acrocentric or telocentric autosomes, eight metacentric or submetacentric autosomes, a large, submetacentric X chromosome and a small acrocentric Y chromosome. (D245)

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Musculo-Skeletal System

Source Information

SUMMARY: --
  • --

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Special Senses and Vocalisations:

Source Information

SUMMARY: 
  • The American black bear's eyesight is poorer than that of humans, but they do have colour vision and at close range they have detailed vision and feed partially by sight. Distance vision may not be sufficient to allow black bears to stalk distant prey.
  • The sense of smell is excellent; they may smell carrion at a distance of more than a mile (1.6 km). Scent is the main method used by a female bear to recognise her offspring.
  • These bears have quite good hearing.
  • There are a variety of vocalisations, including a startled "woof", contented purrs of cubs, shrill howls or squalls of uncomfortable or frightened cubs and an "uh-uh" grunt by females calling her cubs to her.

Vision:

  • Bears have moderate vision. (B147)
  • While the eyesight is poorer than that of humans, they do have colour vision and at close range they have detailed vision. (B406.35.w35)
  • Bears feed partially by sight. (D248.w7)
  • American black bears have colour vision and at close range they have detailed vision. Distance vision may not be sufficient to allow black bears stalk distant prey. (D248.w9)
  • American black bears have good colour vision, not dependent on "bright" colours. They use eyesight during feeding. (J345.3.w1)

Touch/ Tactile

  • --

Olfaction:

  • Bears have an excellent sense of smell. (B147, B424)
  • Black bears have an excellent sense of smell and may scent carrion at more than a mile (1.6 km) away. (B406.35.w35)
  • Scent is the main method used by a female bear to recognise her offspring. (D248.w7, J59.12.w1)

Hearing:

  • Bears have moderate hearing. (B147)
  • Black bears have good hearing. (B406.35.w35)

Taste:

  • --

Temperature:

  • --

Other senses:

  • --

Vocalisations:

  • A "woof" of startlement. (B147)
  • Shrill howls by lonely or frightened cubs. (B147)
  • Young cubs make a contented purr and squall if they are frightened or uncomfortable. (B406.35.w35)
  • Females grunt "uh-uh" to bring her cubs to her, for example calling them out of a tree they climbed for safety. (B406.35.w35)
  • "Small cubs squall when hungry, uncomfortable, or badly frightened and voice a "purr" when comfortable or seeking comfort. This sound resembles a rapid series of grunts rather than the throaty rumble of cats." Older cubs use a "pleading bawl" to their mother and this has been heard once as a call between two yearlings. Females make a "huffing call" to cubs, and a subdued "pump pump pump" call was heard repeatedly from a female to her trapped cub. (D274)
  • A loud "huff" is made concurrently with a sudden protective lunge and swat which may be made towards other bears or to humans. A variable growl may be made before this action by some bears. "The vocalisation leading into the physical action appears as threat under circumstances wherein the threatener is fearful." Huffing is also vocalised prior to charging. (D274)

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Authors & Referees

Authors

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

Referee

David L. Garshelis (V.w98)

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