December is a quiet month for British amphibians and reptiles. All of our native species brumate during the winter, meaning they are dormant with occasional periods of foraging during warmer spells. Amphibians and reptiles overwinter in different habitats, but warm, safe spots such as log piles and compost heaps are often popular choices.
Male common frogs may choose a riskier overwintering strategy. They sometimes decide to overwinter at the bottom of a pond, buried into the mud. This can be a good option as they are unlikely to be disturbed or predated upon, however it can be very dangerous if oxygen levels get too low. Frogs can absorb oxygen through their skin underwater and can tolerate very low levels of oxygen, but they will die under anoxic conditions. However, if there are native oxygenating plants in the pond, then this should ensure sufficient oxygen flow.
Common frogs can also survive if a pond partially freezes, but not if it freezes entirely. As a general rule, ponds with a maximum depth of at least 60cm are safe, but any shallower and there is a high risk of it completely freezing over.