Frogcicles, anyone?

Yesterday (07 February 2016) the temperature in Mt. Pleasant reached a high of 46 degrees Fahrenheit.  A blast of Arctic air is going to hit Mid-Michigan over the next few days, dropping temperatures down to near zero degrees by the end of the week.  This drop in temperature will make survival more difficult for many small animals.  The layer of snow that has been insulating the ground has all but melted away.  Animals such as voles, mice, and shrews are exposed to the elements as they forage.  These species all have high metabolic rates, they need to consume enormous numbers of calories for their size just to counteract the effects of cold.  Exposure for many of these species can quickly lead to hypothermia if they are unable to find enough food to maintain their metabolic rate.

Other small animals are less bothered by the change in temperature.  Some of these species spend the winter months securely hibernating below ground.  Mammals that hibernate reduce their metabolic rate and slowly burn through fat that they accumulated during the summer and fall months.  Even though their body temperature drops it remains above freezing.  For reptiles and amphibians this is not an option.  These species are considered ectothermic - meaning that they rely on the external temperature to regulate their internal temperature.  If the temperature of their surrounding is high so is their internal body temperature; if their surrounding are cold so is their internal temperature.

So how to species such as this survive the lows of winter?  If the temperature of their surroundings drops below freezing so does their body temperature.  This exposes their cells and organs to the dangers of freezing solid.  When a cell freezes, ice crystals form in the intercellular fluid - this can cause the walls of the cell to break, destroying the cell.  If enough cells are destroyed the animal dies.  (The same cellular freezing causes plants to die.)