Searching Texas Caves for Signs of White-Nose Syndrome by Mylea Bayless
I climbed slowly and cautiously down the ledge that February day. My reward, after three days of cold, wet and exhausting underground surveys, was the biggest hibernating bat colony we've found yet. I'm sweating in the cold from anticipation and exertion. But the sight revealed by our roving headlamps was breathtaking: the ceiling of this chamber was covered with hibernating cave myotis (Myotis velifer), a dense expanse of brown fur pocked with countless noses, ears and wrists. This was the largest colony I had ever seen in northwest Texas. Then, as we began counting bats, I found a special treat—a white spot in the sea of brown. It's not every day you get to see an albino bat!
We were surveying select north Texas caves for the presence of hibernating bats and for the dreaded signs of White-nose Syndrome. In four busy days, we surveyed 10 caves and counted more than 8,600 bats. Much smaller numbers of tri-colored bats (Perimyotis subflavus) and Townsend's big-eared bats (Corynorhinus townsendii) share many of the hibernation caves with cave myotis colonies. Thankfully, we found no sick or dying bats and no evidence of WNS or the Geomyces destructans fungus that causes it.
Scientists throughout the American West are conducting similar surveys, searching for evidence they hope never to find, while nervously preparing for the potential arrival of this dire threat that has devastated bat populations in the East. White-nose Syndrome or the fungus has now been confirmed in nine bat species in 21 U.S. states and 4 Canadian provinces.
Northwest Texas is directly in one of the most likely paths as WNS expands into the America West, and may be at particular risk. The WNS fungus was reported from cave myotis in an Oklahoma cave in 2010, although no sign of disease has been identified and the fungus has not been detected since then. Researchers are uncertain how the fungus or the disease might impact western bat species, which typically form smaller, more scattered colonies than most cave-hibernating eastern bats.
Also, the Oklahoma cave was home to Mexican free-tailed bats (Tadarida brasiliensis) as well as cave myotis. The freetails, which do not hibernate, are likely to be spared the devastation of WNS. They might, however, be able to transport the fungus—and this is a very widespread species that migrates 1,000 miles (1,600 kilometers) or more into Latin America, which is so far untouched by WNS.
Our team needed to count the bats we were surveying. That is a surprisingly difficult task, even when the hibernating bats hang perfectly still on cave walls. They cling together in clusters, each bat tucked tightly against its neighbors to maximize temperature stability. Counting a small group of, say, 20 to 50 bats can be accomplished by just looking carefully and quietly with a flashlight. But things get complicated when you're faced with clusters of hundreds or thousands of bats, and even experienced observers often come up with widely varied counts. We photographed these large clusters, then checked our initial estimates by displaying the digital photos on a computer screen and meticulously counting each bat. Still, we are unlikely ever to achieve 100 percent accuracy - you just can't see the bats hidden behind their neighbors—but this added step has improved our results.
In this troubling time of White-nose Syndrome, the decision on whether to enter a hibernation cave is never taken lightly. We constantly evaluate the trade-off between the need for accurate data and the risk of disturbing the bats, which can cause individuals to arouse from hibernation and deplete the critical fat reserves they need to survive the winter. Now we must also consider the additional risk that simply entering the cave could inadvertently help spread the WNS fungus. We now spend hours carefully cleaning and disinfecting our gear to standards set by the U.S. Fish & Wildlife Service, and we decide not to enter some caves at all.
Yet just as the threat of WNS raises the risk of entering caves, it can also greatly increase the need to do so, albeit with great care and consideration. The number of bats hibernating in a site and the complexity of their underground environment are critical in setting priorities for limited conservation dollars. And in most Western states, information about the locations of bat hibernacula and their relative importance is very limited.
The risk posed by WNS drives BCI and our partners to explore alternatives for counting bats. Remote monitoring technologies such as thermal imaging, acoustic monitoring, infrared beam-break systems and Doppler radar ultimately may let us survey caves without entering them, but most systems still need additional testing and development before they will be available for general use.
In the meantime, we still have many more questions than answers about Western bat populations and about cave myotis in Texas, but we are making progress. Cave myotis are colonial, insect-eating bats that usually roost in caves and mines (and occasionally buildings and bridges) throughout the southwestern United States and Mexico. Some cave myotis colonies are known to migrate in spring and fall, while others do not. The reasons for such differences among colonies are not clear.
Biologists are increasingly concerned that these populations may be declining—well before the potential arrival of WNS—because many known roosts apparently have been abandoned. But perhaps they are simply shifting roosts. In Texas, we hope to find some answers by periodically surveying a rotating inventory of hibernacula each winter. This should also provide an early warning of the presence of WNS. BCI is working with a number of partners on similar surveying programs for other bat species around the West, where the specter of White-nose Syndrome is a constant fear.
Walking into one of those great rooms deep underground sometimes makes me feel insignificant. I become instantly aware that my whole life is just a fraction of a second compared with the timeline of this one chamber. The bat colony clinging to the rocky ceiling has probably been using this room for many of my lifetimes. The individuals in the colony change, but the colony itself persists. How many centuries did the bats need to create this mountain of guano on the cave floor? Bats have been roosting here so long that they have permanently stained the rock a deep reddish-brown. I am inspired when I think of this enduring ecosystem. And I am saddened to think that in a few short decades, many of these cave rooms filled with bats might sit empty because of WNS.
We must not let that happen. Throughout North America, dedicated bat conservationists and scientists are working tirelessly to ensure that these underground rooms will forever be filled with bats.
Mylea Bayless is Director of Conservation Programs at Bat Conservation International working out of Austin.
You can help Bat Conservation International and its partners fight the scourge of White-nose Syndrome and other devastating threats against bats. Please show your support at www.batcon.org/donate.
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