A bat hibernaculum is a site — natural or artificial — where bats enter and sustain torpor through winter months, typically between October and April in temperate regions.
**1. Temperature tolerances are narrower than commonly assumed.** Hibernating bats in temperate North America maintain core body temperatures between 2°C and 10°C during torpor. Field surveys conducted by biologists at the Indiana State University Center for Bat Studies between 1991 and 2004 found that hibernacula deviating more than 3°C from a colony's preferred thermal band produced measurable increases in arousal frequency — each arousal consuming roughly 10 days' worth of stored fat reserves.
**2. The largest known hibernaculum in the United Kingdom is located in a disused railway tunnel in County Durham.** The Hawthorn Dene railway tunnel, sealed after the 1968 Beeching network closures, was documented by the Bat Conservation Trust in their 2001 national hibernaculum survey as sheltering an estimated 11,400 individual bats across four species, with the majority identified as Daubenton's bats (*Myotis daubentonii*). The survey classified it as a Site of Special Scientific Interest the following year.
**3. Clustering behaviour in hibernacula appears to be partially learned.** Acoustic tagging studies carried out at the Mammoth Cave National Park system in Kentucky between 2007 and 2011 found that juvenile tri-colored bats (*Perimyotis subflavus*) consistently roosted within 14 metres of their natal colony's prior-year position, even when alternate thermally equivalent sites were available, suggesting site fidelity is transmitted socially rather than encoded genetically.
**4. White-nose syndrome has fundamentally altered hibernaculum ecology since 2006.** The fungal pathogen *Pseudogymnoascus destructans*, first documented at Howes Cave in Schoharie County, New York, penetrates the skin of hibernating bats during torpor, triggering premature arousals and fatal depletion of fat reserves. A 2016 analysis published in the journal *Science* estimated mortality across affected North American hibernacula at between 5.5 and 6.7 million individuals in the preceding decade, with some colonies in the northeastern United States reduced by over 90 percent.
**5. Artificial hibernacula have a documented success rate below 30 percent.** A meta-analysis of 47 constructed bat hibernacula across the United Kingdom, Germany, and the Netherlands — compiled by the European Bat Research Symposium proceedings in 2009 — found that only 13 of the 47 structures were occupied within five years of installation. Researchers attributed low uptake to insufficient humidity control and the absence of what the report termed "olfactory priming," the residual chemical signatures left by prior colonies that naive bats use as prospecting cues.
**6. Some hibernacula have continuous occupation records stretching back to Roman-era infrastructure.** Limestone cave systems in the Périgord region of southwestern France, including several chambers adjacent to known archaeological sites, have yielded bat bone deposits in stratigraphic layers dated by researchers at the Université de Bordeaux to approximately 1,800 years before present — indicating unbroken or near-unbroken use of the same thermal microhabitats across dozens of bat generations, far exceeding the lifespan of any individual colony member.