White-Nose Syndrome

White-Nose Syndrome: New Policies Needed for Cave Management
By Merlin Tuttle

A field team is measuring bat roost stains in a limestone cave in Mexico to assess its approximate past importance to bats. Domed ceilings in warm caves are often extra darkly stained and etched due to heavy use by nursery colonies.

As reported in my keynote address at the 46th annual meeting of North American bat researchers last week, despite our best efforts, WNS has spread rapidly from coast to coast, and there is nothing we can do to stop, slow or find a safe, effective and practically applicable cure. It is here to stay, and eventually will reach every species and habitat that is susceptible. Bats are spreading it far more effectively than humans ever could. It is time to refocus our efforts on helping the few survivors rebuild resistant populations, as apparently has already happened in Asia and Europe.

The overwhelming response from colleagues was that it is time to refocus our efforts on providing the best possible protection at a time when populations are at critical lows. Each winter entry into a bat hibernation site forces at least partial arousals, adding a potentially insurmountable burden to already life-threatening energy losses caused by WNS. No matter how well intended, we can’t afford to risk becoming the proverbial straw that broke the camel’s back.

This small bachelor group of Fringed myotis (Myotis thysanodes) likely has moved more often or has used this site for a shorter period, so its stains are less pronounced.

I was encouraged to speak with several colleagues at the conference who are already documenting apparent recovery of protected colonies of little brown myotis (Myotis lucifugus) in the Northeast. Though this is one of the hardest hit species, current studies are documenting apparent reproductive success and gradual recovery. That’s very encouraging!

It is time to focus all possible resources on protecting surviving remnants from unnecessary disturbance. It is also time to acknowledge that closing all caves, even those never used by bats, is counterproductive, needlessly risking partnerships with cavers that we can’t afford to lose.

These stains illustrate an important characteristic of bat versus mineral stains. Because bat stains result from contact with bat bodies, they are always darkest on distal surfaces, lightest in recessed areas less in contact with bat bodies. In contrast, mineral stains tend to be as dark or darker in recessed areas. Dark stains are most often associated with warm roosts used in summer. They also occur in extra warm parts of hibernation caves, where bats go when awake.

Members of the National Speleological Society have been extremely cooperative during this multi-year period in which access to many of their favorite caves has been denied in hope of slowing the spread of WNS. They have played key roles, contributing financially in addition to helping researchers and resource managers find and protect key sites. Nevertheless, broad cave closures clearly have failed. Though reasonable precautions to avoid disturbance in caves suitable for bat occupancy should continue, there are no further reasons to restrict cavers from using caves which are not suitable for bats.

So how does one differentiate between caves suited for bat use versus those that are not? In the coolest climates caves are seldom used except for winter hibernation, and the opposite is true in the warmest climates. Southern caves are used mostly for rearing young. In intermediate climates, a few typically multi-entrance caves may provide effective cool or warm air traps, and to the extent that their volume is sufficient to trap large quantities of cold or warm air that remains relatively stable, they may provide ideal sites for hibernation or rearing young.

Where roosts have been used for very long periods, especially by nursery colonies in domed ceilings, the limestone becomes etched by CO2 from the bats’ breath, combined with wear from clinging claws. In such locations the harder, distal portions of the limestone surface also become extra darkly stained, sometimes also polished.

Throughout mid-latitudes, where a large proportion of North America’s caves are located, fewer than 10 percent are important for either hibernation or nursery purposes. However, at extreme northern or southern latitudes, large proportions of caves may be important for bats in winter or summer only. A few also may be important as migratory stopover sites.

Some caves harbored truly massive numbers of bats prior to the arrival of human disturbance. This one in northern Mexico shows clear staining and guano evidence of past use by an enormous colony of Brazilian free-tailed bats (Tadarida brasiliensis), one that almost certainly numbered in the 10s of millions. The staining continues for more than a quarter of a mile (0.4 km). Locals report having extracted a truckload of guano daily for more than 20 years.

The largest, most complex caves, with the largest (especially multi-level) entrances have traditionally sheltered the biggest and most diverse bat populations, mostly because they provide the widest range of temperatures, especially important during times of climate change. Any mid-latitude cave that traps and holds large volumes of exceptionally cold or warm air likely has been critically important for bats in the past. Large volume also means improved survival due to less unpredictable fluctuation. When bats are no longer using such caves, it is normally due to human disturbance or changes that have altered air flow unfavorably.

So how does one determine historical bat use? In a large proportion of caves, past use can remain clearly visible for hundreds of years after bats have been extirpated. Most limestone is light in color and is typically stained a rusty reddish color by prolonged bat use. With a little experience bat roost stains are typically easy to recognize. Caves where limestone is too hard or soft for leaving long-lasting stains are rare in North America. Old guano deposits, if not completely obscured by human traffic, may prove additionally useful.

Roost stains in bat hibernation caves are typically lighter and less etched into the limestone compared with those left by active summer colonies. However sites of extra long and intense use sometimes show conspicuous evidence. Stains left by hibernating bats are often on vertical walls in extra stably cool caves that efficiently trap and store cold winter air without freezing. These Indiana myotis (Myotis sodalis) are hibernating in a marginal cave where numbers are declining.

By measuring areas of bat-stained limestone it is possible to make ballpark estimates of past population sizes. Most cave-roosting bats of North America cluster at densities of roughly 200 or more bats per square foot, so by measuring the approximate area of staining, and conservatively multiplying the area times 200, one can gain rough estimates of past population sizes. Certainly, when hundreds, or thousands of square feet are stained, that would indicate a past mother-lode roost for bats.

Even when no bats remain in such a cave, large populations often can be rebuilt if protected from disturbance, and human alterations to air flow are remedied. Cavers are typically the first to discover and report such evidence and already have proven invaluable in restoring some of America’s largest bat populations. This is a time when such cooperation is especially important, potentially contributing greatly to the recovery of cave-dwelling species.

Gray bats (Myotis grisescens) hibernating in Pearson Cave, Tennessee.
These gray myotis (Myotis grisescens) have only moderately stained and etched surfaces at this roost, used since human disturbance forced them to move from a cooler, preferred roost in the same cave.

It is tempting to point out that in North America’s richest cave areas, most caves are unused by bats, and that those used are normally occupied only in summer or winter. Unfortunately, it is the largest, most complex caves that are often the most sought after by both bats and cavers. Nevertheless, when wise managers and cavers cooperate, they will often find that even in these complex caves, bats only need relatively small proportions in any given season, and that parts can remain open to responsible caving during specific times or even year-round.

For example, the famous Fern Cave in northern Alabama includes miles of passages critical to hibernating bats as well as miles of passages of extraordinary interest to cavers but not to bats. For more than 20 years, responsible members of the Huntsville Grotto of the National Speleological Society played a critical management role through a cooperative agreement. As site managers, they

This is an example of heavy use of a limestone crevice, over many years, by a small group of bats. Notice the heavy etching and dark staining at the edge, where bats can most easily cling to the surface. The staining gradually fades with increasing distance from the crevice.

regulated access in a manner very helpful to responsible cavers, to more than a million hibernating bats and to the U.S. Fish and Wildlife Service (the owner responsible for its protection).

The agency lacked the manpower and resources necessary to provide adequate protection for this remote property, so were happy to have onsite help from the Huntsville Grotto. Organized cavers were present year-round in the parts unused by bats, and near enough to check the entrance to hibernation areas for possible vandals or other problems. They also were able to use the bat area during the bats’ summer absence. Cavers provided the eyes and ears the Service lacked and did an exemplary job of ensuring that only authorized, supervised entry occurred.

One hundred thousand gray bats hibernating at 32 degrees F in Pearson Cave, Tennessee.
One hundred thousand gray myotis hibernating at 32 degrees F (O degrees C) in a Tennessee cave. These bats roost in an incredibly stable cold air trap just 50 feet (15 m) from the cave entrance only when they remain undisturbed for several years. When disturbed they move to inner areas and decline in numbers due to the increased cost of hibernation at higher temperatures.

Unfortunately, when WNS became a threat, the cooperative management agreement was canceled, and no further entry by organized cavers into any part of the cave was permitted. The subsequent lack of regular monitoring by trained grotto members resulted in extensive vandalism when the government was unable to protect it from entry by an uninformed public. Moreover, the official closure appears to have had no effect in preventing the arrival of WNS. I hope this sad lesson will serve as an example of the importance of cooperation between cave owners and managers and responsible members of organized caving groups.


White-Nose Syndrome: Origin, Impact and Management

By Merlin D. Tuttle

White-nose syndrome (WNS) impact on bats - photo by nancy heaslip
WNS infected bats.

White-nose syndrome (WNS) is caused by a fungus, Pseudogymnoascus destructans (formerly known as Geomyces destructans). It was first recorded from a photo taken in a cave in Schoharie County, New York in 2006. By the summer of 2014, it had spread across most of eastern North America (25 states and 5 Canadian provinces). In 2015 it reached Nebraska and in early 2016 had also been detected in Washington State.

It appears to have come from Europe via accidental introduction. But we still don’t know how it arrived. It has been hypothesized to have come on the shoes or clothing of a person who contacted it in a European cave, then visited a commercial cave in New York. However, in attempting to explain its sudden appearance in Washington State, Dr. William Halliday has pointed out a possibly more plausible explanation. He notes that, in both New York and Washington, the first sick bats were found within about 30 miles of a major shipping terminal where large quantities of freight are unloaded from Europe and Asia, and that bats have been known to “hitchhike” in large storage containers. It will be interesting to see if fungal cultures from Washington State versus New York can shed light on this intriguing question.

In eastern North America WNS has killed up to 90% of some species that hibernate in caves (especially little brown bats, northern long-eared bats and tricolored bats), with death tolls ranging in the millions. Other cave-hibernators, such as endangered Virginia big-eared and gray bats, seem to be unaffected. Additionally cave-dwellers that don’t hibernate, as well as tree-dwellers appear to be unaffected.

Infections cause bats to arouse too often from hibernation, exhausting limited fat reserves before they can feed again in spring. Though not yet proven, it seems likely that mortality will be heaviest where winters are longest.

Though WNS has had devastating impact on populations of bats that hibernate in caves, it also has provided an unprecedented opportunity to educate millions of Americans regarding the values of bats as insect predators and has stimulated the first widespread summer monitoring of status trends.

It is important to note that European bats appear to have already developed resistance to this fungus. And available evidence suggests that, with careful protection, small numbers of survivors in America will also be able to slowly rebuild immune populations.

I believe we are well past the point of stopping or even slowing this now widespread infection. The guiding principle must be “first, do no harm.” Killing infected bats is pointless, and attempting to decontaminate natural roosts with toxins or foreign organisms could result in disastrous unintended consequences. Finally, treating individual bats is impractical at more than a small, local scale, and it remains to be seen whether treated individuals will then be resistant to reinfection.


Our best remaining options are to: 1) strictly avoid further winter disturbance, 2) increase year-round protection of all roosts, 3) educate the public to overcome fear and understand the values of conserving bats and 4) promote minimally invasive research to better understand bat needs and status trends.


Aside from strict protection of bat roosting sites, especially in winter, there appears to be no further justification for closing caves. Organized cavers have proven themselves to be invaluable leaders in detecting sites in need of protection, in building and monitoring protective gates and in informing state, federal and private managers of vandalism. We owe a special debt of gratitude for their invaluable cooperation and leadership despite the fact that this crisis often has excluded them from their favorite places.

For more WNS information, please refer to our blog posts.