If you drive south on I-75 from Louisville, Kentucky for about 90 miles, you’ll come across the longest known cave system in the world. Mammoth Cave National Park is famous for its nearly 400 miles of caves and hosts well over half a million visitors a year. But the park is also home to researchers who have been documenting a disturbing trend known as White Nose Syndrome that has spread across cave systems in North America and has caused millions of bats to die.
The problem has spread over the last 10 years from New England down through the Midwest and is now affecting caves as far as Texas and Washington state. Last June, I traveled to the park to get a better understanding of what is happening to bat populations from the scientists themselves. Dr. Rick Toomey, director of the Mammoth Cave International Center for Science and Learning, was my guide around the park’s research facilities and gave me insight on exactly happening to the bats in the park.
A spreading pandemic
In the winter of 2006-2007, scientists working in the caves of upstate New York began noticing a strange trend. When conducting regular data collection, researchers walked into caves with floors covered with dead bats. In some cases, it was nearly impossible to walk without stepping on the dead bodies. The researchers also noticed a white fungus on the noses of the dead bats.
White Nose Syndrome (WNS), as the scientists came to call this phenomenon, is a caused by a superficial fungus that colonizes on the bat’s skin, particularly on and around the face and wings. Similar to the fungus that causes athlete’s foot, WNS acts an irritant and thrives in areas that are cold and damp, making caves the perfect environment to grow.
While the fungus itself does not seem to be toxic, the issues arise during the winter when bats are hibernating. The irritating nature of the infection causes the bats to wake up from their hibernation, which causes them to burn significantly more calories and depletes their fat reserves meant for their dormant state. Since there is little food in the winter for bats to eat to support their awake state, the bats then simply die of starvation.
Serious risk of becoming endangered
Over the last few years, White Nose Syndrome has spread from the Northeastern United States down throughout the Midwest. Eventually, the disease reached Mammoth Cave National Park and has decimated the populations of most of the park’s 12 different bat species. Dr. Toomey, who has coordinated the research on the park since 2005, estimates that nearly 6 million bats have succumbed to the White Nose Syndrome. Little brown bat and the tricolored bat have been hit particularly hard, with populations declining by over 90% over the last 10 years. “It’s devastating to the species,” says Dr. Toomey. “Our bats are at serious risk of becoming endangered.
Most cases, the disease is spread directly from individual to individual, making species who hibernate close together more susceptible to White Nose Syndrome. Some species, such as the small-footed, gray, and evening bats, have experienced minimal deaths, losing only around 20% of their populations due to the fact they don’t colonize close together or tend to live in trees instead of caves. However, human activity has been playing a major part in transmitting the fungus as well. People who enter caves without decontaminating their gear, often inadvertently bring the fungus with them, contributing to the spread of WNS.
Why White Nose Syndrome a problem?
Marissa Thalken, who at the time of my visit was researching northern long-eared bat populations, explained that bats do a lot of things within an ecosystem, but perhaps their most important are role is that of pollinator. Many species of bats use nectar for a food source. When they go from flower to flower to suck down the plant’s sugary goodness, they also spread pollen, allowing the plant to be fertilized and reproduce. While no study has been finalized as of yet, the decline in bats, and other pollinators such as bees, could seriously hurt the tobacco and soybean farms around Mammoth Cave.
Yet these animals are no one trick pony. In addition to helping facilitate pollination, some bats even help in seed dispersal, by eating fruit and then spreading the seeds through their droppings. Bats also tend to eat a lot of insects. Aside from being pests to both humans and other species, some insects can be vectors for diseases. Bats are able to keep these populations down, which make for healthier plants and keep transmission rates low. There are studies going on right now in Mammoth Cave National Park that is looking to see if insect populations are on the rise as bat populations struggle.
Bats also can be the basis of entire food webs. Most ecosystems on Earth are directly powered by the Sun: plants capture light energy through photosynthesis and provide food for all other organisms. But as you may have seen yourself, there is no sunlight in caves. Yet, there is also no lack of organisms or biodiversity. So how are all these species able to survive without a direct energy source? The answer lies in the bat’s droppings or guano. Bats are one of the few species that travel in and out of the cave environment. When bats leave their caves in the night, they go to eat plants and insects. Upon their return, their droppings provide energy for the rest of the cave ecosystem.
Wildlife capture is an important technique used by scientists across the world to collect valuable data. The researchers at Mammoth Cave National Park been using this procedure to get population estimates, track the movement of individuals, and to collect data on the overall health of a population.
However, this is no easy task. The process involves getting to a cave entrance around sunset, a commute that could take an hour or more, including trekking in equipment. A large, fine net is then untangled and set up at the mouth of the cave, which (sometimes) ensnares the bats as they leave the cave for their nighttime hunt for food. The procedure requires a lot of sitting in the dark while waiting for a bat to get stuck so you can take some data. This process can take hours, with some scientists staying out until 3:00 or 4:00 in the morning to collect specimen.
Thalken and Dr. Toomey took me out on one such capture. While it may be intuitive, wildlife capture is a tedious business. My job was to hold the infrared sensor, which gives temperature readings of the surrounding environment and can show when a warm-blooded bat is snared in the cool air coming out from the cave. It’s a lot of waiting and looking at the IR display, and a lot more waiting. According to Dr. Toomey, just 10 years prior, most captures were able to collect 30 specimens a night. In 3 hours of watching for bats to come out from the cave, we only captured one, evidence of the devastating toll White Nose Syndrome has taken on the bat populations at Mammoth Caves.
What can be done?
Bats are in need of homes, especially as humans continue to develop further and further away from city centers and segment their forest habitats. Maintaining bat boxes are a great way to give these creatures shelter and can be maintained in both rural and urban environments. It’s also important to stay away from caves where bat colonies hibernate in the winter. Not only is it then easier to infect the cave ecosystem with the White Nose Syndrome fungus, but your presence alone can disturb hibernating bats, causing them stress and waking them from hibernation.
This is not to say that caves need to be avoided completely. It’s important that the public is able to appreciate these beautiful, natural spaces. If you do go caving make sure that any clothing or equipment is decontaminated upon entering and leaving the caves. Mammoth Caves National Park has excellent cave tours that vary from easy 30 minutes walks, to strenuous 4-hour excursions and they do a great job of making sure that everyone who visits is decontaminated from the fungus.
- The US Fish and Wildlife Service has a list of 10 things you can do to help bat populations, including some citizen science: https://www.fws.gov/midwest/endangered/battips.html
- Visit Mammoth Caves, Carlsbad Caverns, or Wind Cave National Parks, all with excellent cave systems that can teach you all about their geology, biology, chemistry, and history.