Infectious diseases are not the only cause of amphibian mortality. Dead amphibians, sometimes in large numbers, can also be the result of non-infectious events such as ‘winterkill’. Some amphibians, mostly common frogs (Rana temporaria), might overwinter in the silt and vegetation in the bottom of ponds, which usually does not harm the animals. However, sometimes they don’t survive hibernation due to winterkill, which usually occurs if the pond becomes frozen over. The exact cause of this is not yet known, but it is thought to be caused by lack of oxygen or potentially the toxic effect of gases produced by decomposing organic material beneath the ice during long cold spells. Alternatively, winterkill can affect frogs overwintering in very shallow ponds if the entire water body freezes.
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