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.  Photo taken by Scott Cooper
 
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 37C to about 2-4C 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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