Hibernation
Throughout mid-March until mid-October the ground squirrels are
diurnal active when the sun is shining. If the sun is not
shining and the weather is dreary, the squirrels spend most of their
time in their warmer burrows away from predation. Food is
normally consumed during this time period and the carbohydrates from
the food are oxidized. Months before hibernation,
food is
cached and is stored as white and brown adipose tissue in the body.
Body weight doubles in most cases during this pre-hibernation
period. Nuts and seeds are also gathered and horded in their
hibernating burrows for a food source after arousal from hibernation
when food is scarce. Day light hours become shortened and
temperatures become cooler during the fall months which help to
trigger these pre-hibernation preparations.
Hibernation is an extended time period of physical inactivity with
extreme decreases in physiological activity which occurs
mid-October. The animals body temperature drops from about 37°C to
about 2-4°C along with the heart rate dropping from about 200bpm to
only 3-5bpm. Oxygen consumption lowers to only 2-4% of normal
due to the respiration decreases from 100-200breaths/min to only
4-6breaths/min. Metabolically the squirrels are not eating
during this time period and their metabolism is only 2-4% of what it
normally is. Stored lipids within the white adipose tissue are
hydrolyzed to be used as an energy source. The immune system is
essentially suppressed and cold inactivation of the nervous system
consequently causes loss of somatic reflexes. Research has
shown to account for these extreme physiological conditions, various
blood clotting protein levels are decreased and blood clotting
inhibitor protein levels are increased.
This state is not continuous over the six month period.
Arousals due occur about once a week where the body temperature
rises back to normal and decreases to a hibernating temperature.
Overall, this process lasts for only16 hours. During these arousals
the squirrel is then able to activate their immune system to fight
off infections such as those caused by bacteria.
Mid-March the male squirrels begin arousing from hibernation and a
few weeks later the females arouse. After the long winter the
squirrels are a measly one-third of the weight they were
pre-hibernating. Hoarded food in their burrows is available
for them to eat from the previous fall. This food is a
necessity since food is not readily available in the spring and
metabolically their body is not up to par with the energy
expenditure taken to gather and find food after arousal.
Benefits of hibernation not only include surviving the harsh winter
climates and scarcity of food. Decreased predation if the
squirrels are in their burrows during hibernation is also
beneficial. An increased lifespan is observed due to the fact
the body is not being worked constantly over the course of a year
which increases the number of reproductive seasons. This increases
the amount of offspring their genes can be passed down to
additionally.
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