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Cave Conundrum: Is White-Nose Syndrome Responsible for All Declining Bat Populations?

Hibernating bat populations across the Eastern United States have suffered declines since the 2000s. Little brown bat populations have declined 70 percent or more. Populations of the northern long-eared bat and tricolored bat have declined by 30 percent. The scientists studied these three bat species in their research.

The cause of bat population declines is often assumed to be white-nose syndrome (WNS), a deadly disease caused by a fungal pathogen. Evidence suggests WNS is a serious threat to bat populations. However, research has not yet supported WNS as the only cause of bat population declines. Therefore, the scientists in this study asked: Is WNS the sole cause of these bat population declines, or is there something else causing bat populations to decline?

Cave Conundrum: Is White-Nose Syndrome Responsible for All Declining Bat Populations?

Meet the Scientists

Sybill Amelon

Wildlife Ecologist

Brent Sewall

Biologist

What Kinds of Scientists Did This Research?

Wildlife ecologist: This scientist studies the relationship of different kind of wildlife with each other and with their living and nonliving environment.
Biologist: This scientist studies living organisms and living systems.

Thinking About Science

Research questions in science often require a large amount of information to get an accurate answer. Sometimes, scientists discover that there is not enough information to get an accurate answer to a research question. To solve this problem, some scientists begin long-term research studies. For instance, scientists may want to know how drought affects pine tree growth.

First, they would want to know how pine trees grow in both non-drought years and drought years. They would need many years’ worth of data to understand normal pine tree growth before determining how drought might change that growth.

In 1908, the Forest Service recognized the need for long-term research sites. The Forest Service established a system of Experimental Forests and Ranges (EFRs) (figure 1). At these sites, scientists regularly collect information about the rainfall, soil, plant and animal populations, and other environmental conditions of the area. By recording these data over many years, EFRs provide a broad range of information that can help scientists answer complex, long-term research questions. Similarly, in this research about white nose syndrome, scientists needed to gather research over a longer period of time.

A map of the United States with dots on all the Experimental Forest and Ranges — **Figure 1**. Today, 80 experimental forests and ranges are spread across the United States. FIND Outdoors map by Carey Burda and Stephanie Pfeiffer.

Thinking About the Environment

White-nose syndrome (WNS) is a disease affecting hibernating bat populations. The disease is named for the white fungus that collects on the muzzle and other parts of infected bats (figure 2).

A close up of a bat with white fungus growing on it's nose — **Figure 2**. Scientists can identify WNS on bats from the white fungus that develops on the bat’s nose and damaged skin on the bat’s
body. U. S. Fish and Wildlife Service photo by of Jonathan Mays.

The disease was first introduced in New York in winter of 2006. Since the time WNS was first introduced, the disease has spread to caves and mines across 33 States and 7 Canadian provinces. WNS has killed an estimated 6 million bats in the Eastern United States and Canada (figure 3). At some sites, 90 to 100 percent of bats have died from WNS infection.

Scientists are dedicated to understanding and combatting WNS because bats are important to the ecosystems in which they live. In some ecosystems, plants rely on bats to pollinate flowers or spread seeds. Bats, the only free flying mammal, are also an important indicator species that signal changing conditions in an ecosystem. Some bat species are insectivores, and act as a natural method of pest control in their environment.

A map of the United States showing white nose syndrome occurence in different counties by year — **Figure 3**. Since its introduction in New York in 2006, WNS has spread across the Eastern United States as well as other areas. U. S. Fish and Wildlife Service map by https://www.whitenosesyndrome.org.

Number Crunch

Introduction

Hibernating bat populations across the Eastern United States have suffered declines since the 2000s. Little brown bat populations have declined 70 percent or more. Populations of the northern long-eared bat and tricolored bat have declined by 30 percent (figures 4, 5, and 6). The scientists studied these three bat species in their research.

A small brown bat hanging upside down in a cave — **Figure 4**. The little brown bat is small, usually weighing less than half an ounce.

U.S. Fish and Wildlife Service photo by Marvin Moriarty

Northern long-eared bat hanging upside down in a cave — **Figure 5**. Northern long-eared bats are known for their especially long ears.

U.S. Fish and Wildlife Service photo

A bat resting in a cave — **Figure 6**. Tricolored bats, like the one pictured, rest in dead leaves or the needles of trees.

U.S. Fish and Wildlife Service photo by Pete Pattavina

The cause of bat population declines is often assumed to be WNS, a deadly disease caused by a fungal pathogen. Evidence suggests WNS is a serious threat to bat populations. However, research has not yet supported WNS as the only cause of bat population declines. Therefore, the scientists in this study asked: Is WNS the sole cause of these bat population declines, or is there something else causing bat populations to decline?

The scientists hypothesized that if WNS is the sole cause of decline in bat populations, then the following conditions will be true:

Only bat populations infected with WNS will experience declines;
Declines in bat populations will happen later at caves farther from where WNS was discovered; and
Bat populations will begin declining shortly
after WNS infects a colony.

Reflection Section

Methods

To test their ideas, the scientists needed to know how bat populations have changed before and after WNS was introduced. They needed a large amount of information about bat populations over a period of many years to understand population trends. They used data collected by State wildlife agencies in New York, Pennsylvania, West Virginia, and Tennessee. These data were gathered during regular surveys of bat hibernacula during winter every 2 years between 1999 and 2011 (figure 7).

Many pats piled up together hibernating in a cave in the winter. — **Figure 7**. Many species of bats hibernate throughout winter in caves, mines, and other cold, dark places. These sites are called **hibernacula** (hī bər na kyə lə).
U.S. Fish and Wildlife photo by Keith Shannon.

Biologists visited the same hibernacula to collect data on the location of caves, the number of bats, and presence or absence of WNS (figure 8).

A scientist holding a bat's wings open. — **Figure 8**. During the surveys, biologists found
WNS present in approximately 44-48 percent
of the routes they surveyed for all three species.
U.S. Fish and Wildlife Service photo by Gary Peeples.

The scientists graphed the population trends of each bat species in each State using the data. They also graphed the expected scenarios, or models. These models illustrated how the bat populations would change over time if all three of the hypothesized WNS conditions were present. By comparing the results of the models with the graphs of actual population trends, the scientists were able to evaluate whether the hypothesized conditions were true.

Reflection Section

How Do Scientists Detect WNS?

When scientists survey caves, they look for signs of WNS. Visible signs of WNS include skin damage, white fungus on the bats’ noses, and the number of dead bats in the cave. However, these visual methods are not always an accurate way to detect WNS. New research has found a way to detect a WNS infection using a certain range of light. Ultraviolet light, which is invisible to the human eye, makes the skin damage caused by WNS glow an orange-yellow color. A study showed this method was 98.8 percent effective at positively detecting WNS, and it provides a new, reliable way to identify WNS on bats.

Source: “Black-Light Detects White Nose Syndrome in Bats,” by U.S. Geological Survey.

How Do Scientists Make Models?

You probably have seen toy cars and airplanes that look just like the real thing, only smaller. These toys are actually models, or simplified representations of a larger item. Models are used frequently in our day-to-day lives to help people see and understand large objects, concepts, and processes.

Scientists also use models when a scientific research question is too big or too complicated to answer. In these situations, scientists may use scientific modeling. A scientific model uses data to represent complex scientific concepts in a simpler way. In the case of this study, the scientists used models to better understand how a disease, like WNS, affects bat populations.

Models are useful tools for scientists, but they are only as good as the data that are put into them. The scientists in this study used data taken from four States across 11 years. Using this quantity of data helped the scientists increase the likelihood that their model would give them an accurate representation of the bat populations they were studying. In the table below, the total numbers of surveys conducted, routes traveled, and individual bats counted are shown. The scientists used this information to build their model (table 1).

A graphic of a table used in the study — **Table 1**. This table shows the set of data the scientists in this study used to make their model.

Findings

The scientists compared the modeled and real population patterns. The data showed all three of the bat species met at least one of the three hypothesized conditions. However, none of the species met all three conditions (table 2). Results indicate that certain bat populations were declining before WNS was discovered in those populations. Other bat populations were experiencing a population increase that continued despite WNS infection.

Table 2. This table shows whether or not the modeled bat populations met the three hypothesized conditions.
Hypothesized Condition	Little Brown Bat	Nothern long-eared bat	Tricolored bat
1. Only bat populations infected with WNS will experience declines	No; Bat colonies with and without WNS experiences similar population changes	No; Bat colonies with and without WNS experiences similar population changes	Yes; Bat colonies with WNS declined more severely than bat colonies without WNS
2. Declines in bat populations will happen later at caves farther from where WNS was discovered	No; Patterns varied greatly by region, though most areas experienced declines	Yes; Declines were slower and less severe further from the point of WNS introduction	No; Declines did not vary with distance from the point of WNS introduction
3. Bat populations will begin declining shortly after WNS infects a colony	Yes; Onset of bat population declines matched local detection of WNS within 1 year	No; Bat population declines began before local detection of WNS by 10+ years	No; Bat population declines began before local detection of WNS by 3-7 years

Reflection Section

Discussion

The results of the study support the idea that WNS is an important cause of decline of bat populations in the Eastern United States. However, the results indicate that WNS is not the only cause of decline. Most efforts to aid bat populations have focused on preventing transmission of WNS by humans (figure 9). However, WNS also is often transmitted through non-human means, like one bat contacting and infecting another bat.

A sign on a tree designating the area as restricted due to hibernating bats — **Figure 9**. Federal and State agencies close caves where endangered bats hibernate to prevent disturbance from human visitors. U.S. Fish and Wildlife photo by of Ann Froschauer.

The findings in this research also suggest that there are other important causes of decline that may be overlooked. Other potential sources of mortality include agricultural pesticides and chemicals, climate change, collisions with human-built structures and vehicles, and habitat loss or degradation of habitat. These results suggest that scientists should continue to combat WNS while also addressing other threats to bat populations.

Reflection Section

Adapted from Ingersoll, Thomas E.; Sewall, Brent J.; Amelon, Sybill K. 2016. Effects of white-nose syndrome on regional population patterns of 3 hibernating bat species. Conservation Biology. 30(5):1048-1059

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Caves and Karst Natural Inquirer - Vol. 20 No. 1

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Meet the Scientists

Introduces students to the scientists who did the research. This section may be used in a discussion about careers in science.
What Kinds of Scientist Did This Research?

Introduces students to the scientific disciplines of the scientists who conducted the research.
Thinking About Science

Introduces something new about the scientific process, such as a scientific habit of mind or procedures used in scientific studies.
Thinking About the Environment

Introduces the environmental topic being addressed in the research.
Introduction

Introduces the problem or question that the research addresses.
Method

Describes the method the scientists used to collect and analyze their data.
Findings & Discussion

Describes the results of the analysis. Addresses the findings and places them into the context of the original problem or question.
Reflection Section

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Number Crunches

Presents an easy math problem related to the research.
Glossary

Defines potentially new scientific or other terms to students. The first occurrence of a glossary word is bold in the text.
Citation

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FACTivity

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In this lesson plan, students will complete a guided reading activity while reading their chosen article. As they read, they will complete a double-entry graphic organizer where they will note...
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Meet the Scientists

Sybill Amelon

Brent Sewall

What Kinds of Scientists Did This Research?

Thinking About Science

Thinking About the Environment

Number Crunch

Introduction

Reflection Section

Methods

Reflection Section

How Do Scientists Detect WNS?

How Do Scientists Make Models?

Findings

Reflection Section

Discussion

Reflection Section

FACTivity – Cave Conundrum

Glossary

degradation

hibernacula

indicator species

insectivore

mortality

pathogen

representation

route

transmission

Sybill Amelon

Brent Sewall

Standards addressed in this Article:

Social Studies Standards

Note To Educators

The Forest Service's Mission

What Is the Natural Inquirer?

Meet the Scientists

What Kinds of Scientist Did This Research?

Thinking About Science

Thinking About the Environment

Introduction

Method

Findings & Discussion

Reflection Section

Number Crunches

Glossary

Citation

FACTivity

Science Education Standards

We Welcome Feedback

Contact

Email

Lessons

Lesson Plan – Haikus

Education Files

Project Learning Tree

Related Resources from the Natural Inquirer

The Trees Have Gone Batty! How Bat Scat Helped Restore a Tropical Forest

Moving Spore-adically: The Spread of Sudden Oak Death in California Forests

Additional Resources

USDA National Invasive Species Information Center: White-Nose Syndrome

National Park Service: What Is White-Nose Syndrome?