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Bat Conservation in Winter


New Jersey has had an active bat conservation program for many years. One of the most important goals has been protection of winter dens, where bats from across the landscape gather together for hibernation. Winter colonies often number in the hundreds or thousands due to the sparse availability of suitable hibernacula. Bats are especially vulnerable to disturbance and vandalism during hibernation, when even passive human activity can arouse the bats from torpor, causing them to burn through their energy reserves too quickly. Preserving lands that contain hibernacula and installing bat-friendly (people-proof) gates are key to conserving bat populations.

NJ's best-known example is the Hibernia Mine in Rockaway Township, Morris County. Hibernia was among the state's largest iron ore producers - active from the early 1720s until operations ended around 1913. Bats were first observed in the abandoned mine in the 1930s, and by the 1980s more than 20,000 bats were wintering there each year. At the same time, vandalism and trespassing were getting worse, and several attempts were made by the landowners to keep people out. Once a small number of federally endangered Indiana bats were found using the mine in 1992, a multi-partner plan kicked into gear to finally gate the site (Dutko 1994). The State acquired the property soon thereafter via our Green Acres Program; it is now part of the Wildcat Ridge Wildlife Management Area.

Surveying bats in a Sussex County mine.
John Gumbs of BATS Research Center, surveying bats in a Sussex County mine.
Click to enlarge

The story of Hibernia Mine continues to be written. The hibernating colony climbed to around 30,000 bats in the early 2000s, with Little browns (Myotis lucifugus) being most numerous but bats of all cave-hibernating species seeking refuge there. Sadly, White-nose Syndrome hit Hibernia in January 2009, and in what seemed like an instant, more than 90% of the bats had died.

The ENSP and our partners have used Hibernia as a living laboratory of sorts, tracking the impacts of WNS on a well-studied and easy-to-observe population of bats. There, BATS Research Center pioneered the use of long-wave Ultraviolet light as a nonlethal, on-site tool for detecting WNS that's as accurate as microscopic skin tissue analysis (Turner et al. 2014). Multi-year banding/re-sighting census data of Hibernia's Little brown bats are showing improved WNS survival with each passing year, although annual survival is still below pre-WNS levels (Maslo et al. 2015).

Hibernia Mine Population Trend 1995-2017
Hibernia Mine Population Trend 1995-2017
Click to enlarge

Surveying bats in a Sussex County mine.
A newly banded Little brown bat. Bands are uniquely engraved to help biologists learn about bats' movements and longevity…and now to monitor their survival in the era of White-nose Syndrome.
Click to enlarge
In fall 2017, it came time to replace Hibernia's bat gate. The ENSP and BATS Research Center took the opportunity to remove a large center portion of the concrete wall that stood just behind the original gate; an artifact of the prior landowner's efforts to keep people from getting in. The wall gave little room for bats to negotiate their ingress and egress through the portal, but it also inhibited cold air flow into the mine shaft during hibernation.

While bats do need above-freezing temperatures for most of hibernation, researchers have documented bats shifting to colder parts of their hibernacula (especially temperatures ≤41°F) in the years following White-nose Syndrome (Butchkoski et al. 2014). As it turns out, the Pd fungus does not grow well below that threshold (Reynolds 2017). Temperature loggers are monitoring the before-and-after conditions throughout Hibernia's 2,300-foot long shaft, and biologists will compare the locations of hibernating bats to available temperatures now that the wall has been removed.

Hibernia Mine is just one of about 20 known bat hibernacula in NJ, each with its own storied history. About half of these sites are now on preserved open space, and gates are in place to safeguard about 98% of our state's known hibernating bat population. Time will tell what the future holds for these bats - whether they'll continue to trend downward toward extinction or begin to rebuild in the wake of White-nose Syndrome.

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Department of Environmental Protection
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Last Updated: November 8, 2017