Newt
During the subsequent few months, the larvae undergo metamorphosis, during which they develop legs, and the gills are absorbed and replaced by air-breathing lungs. Some species, such as the North American newts, also become more brightly coloured during this phase. Once fully metamorphosised, they leave the water and live a terrestrial life, when they are known as "efts". Only when the eft reaches adulthood will the North American species return to live in water, rarely venturing back onto the land. Conversely, most European species live their adult lives on land and only visit water to breed.
Hibernaculum (zoology)
The microclimate refers to the climate of a very small or restricted area, like the hibernaculum, especially when this differs from the climate of the surrounding area. Overwinter survival in these cricket frogs among other frogs is dependent on using hibernacula with appropriate physical microclimate characteristics, such as moist soil, that buffer frogs from temperatures that drop below the freezing point of the body fluids for extended periods. Although, determining if frogs can identify sites with appropriate microclimates to support overwinter survival and what factors might inform such choices are still unknown and will require further study. Therefore, it is still not known to what extent various types of prospective hibernacula for frogs might be suitable in the years to come, especially factoring in climate change.
As part the Highways Agency Biodiversity Action Plan (HABAP) in the UK, the Species Action Plan (SAP) for great crested newts aims to maintain and enhance existing newt populations through appropriate management of suitable habitat. As part of steps to implement the HABAP, newt hibernacula (e.g. log piles) have been constructed to improve the quality of the terrestrial habitat through increasing the number of potential overwintering sites. It was also determined that habitat surrounding breeding ponds with plenty of cover and suitable overwintering sites may have less need for provision of artificial hibernacula than landscapes with less woodland, hedgerows, scrub etc. Because great crested newts show high loyalty to over-wintering locations, returning to such established areas year after year, artificial hibernacula could be important in future years to conserve newts and other amphibians. Although, monitoring in the vicinity of these hibernacula in autumn using felt roofing tiles did not reveal the presence of any great crested newts even though they are known to breed in nearby ponds. Common toads and frogs did surround the area however. Therefore, further studies need to be conducted in order to create species-appropriate artificial hibernacula.