CALL OF THE URBAN WILD

Hoary Bat

with Liza Lehrer

In summer 2017, urban wildlife ecologist Liza Lehrer and her team at the Urban Wildlife Institute, a research center at Lincoln Park Zoo, installed a passive acoustic monitor on the Studio’s rooftop to gauge bat activity in the area. We spoke with Liza about her project, the benefits of bats, and what people can do to support bats in urban environments.

Can you start by explaining your project?

The bat biodiversity monitoring project is part of a larger urban biodiversity monitoring project that we’ve been working on at Lincoln Park Zoo since 2010. The bat component started in 2013. The idea behind it, and all the research that we do, is to better understand how wildlife lives in cities and how best to use that information so that we can manage conflict and coexist, because we’re seeing more and more species that are able to adapt to being around humans and thrive in urban landscapes. It’s an exciting phenomenon and it will continue to increase as more people are living in cities and natural habitat is declining. We’re trying to understand what species are out there, what are the habitat predictors that drive their distribution, and why do we see a lot of species diversity at one site but fewer species at another site. We’re also trying to understand humans’ role in this—what are the anthropogenic factors?

For bats specifically, ambient noise is a major issue. So how are traffic, airplanes, and all the other noise that we create as humans affecting bats in the city? Artificial light is another factor, so how are streetlights and illuminated billboards, and the change to LED lights, affecting bats? We know that some bats are attracted to those lights because they attract insects, so they will congregate and feed in those areas, but some bats will avoid them. We’re looking not only at how those drivers and factors are affecting bat species but how those conditions are changing over time. We’re continuing to monitor our sites every year as well as expanding the number of sites.

This study is especially important because bats are facing a lot of threats right now, most notably white-nose syndrome, which is a pathogen that’s been spreading across the country and was found in Illinois in 2012—right before we started the study. So a key part of our work is tracking these populations over time to see how they’re doing; for example, are we seeing fewer species at a site than we did pre-white-nose syndrome?

Is white-nose syndrome caused by humans?

Its source is a naturally occurring fungus in Europe and bats there have, for the most part, adapted to living with it and don’t have any negative effects. For bat species

here in the United States, it was a novel introduction, and without any adaptation to the fungus and the pathogen it causes, there have been serious consequences. Researchers suspect that the fungus was brought to the US by humans, so it was probably brought over on someone’s boots, equipment, or clothing, or another item that was brought into a cave. This hasn’t been established for sure, however. It was first found in 2006 in upstate New York and has now spread rapidly across the country to the point that I think it’s been found as far as upstate Washington.

And it wakes them up out of hibernation?

Yes. It’s found in cave-dwelling bat species because the fungus thrives in cool, damp environments, where they’re exposed to it during hibernation. The pathogen wakes them up and eventually causes them to starve because it’s winter—there’s no food to eat and they’re using all their fat stores. If they can make it through the summer they can shed the pathogen, but then they can get reinfected when they go back to the same cave. Researchers have documented in some species up to a 90 percent mortality rate.

In Chicago, there are two general groupings of bat species: the cave-dwelling bats and the migrating tree bats. The cavedwelling bats are the ones that are vulnerable to this pathogen, but the migrating bats face other threats; a major one is wind energy development. There have been many documented bat mortalities due to wind turbines.

The good news about this, though, is that there are effective mitigation strategies that have been adopted by many wind energy companies. A lot of it is slowing down the turbines during peak migration periods. Bats aren’t very active when it’s windy, so the timing lines up well. We don’t really have bats that are overwintering in Chicago; they all generally leave to go hibernate in nearby caves or they migrate farther south to warmer areas.

What species do you expect to find in the Chicago area or that are part of your study?

What’s exciting about what we’ve discovered so far is that we’ve documented a large diversity of species living in this region and even a lot of diversity right here in the city. Included in the study area are about nine rural or exurban sites, and those are located in western Kane County, which is a very different landscape than Chicago. The sites are either forest preserves or golf courses, and they’re primarily surrounded by intensive agriculture. Within Chicago, we have a lot of variation in site types— rooftops, parks, some golf courses, and forest preserves—and geographically those range throughout downtown Chicago and Cook County.

What we’re seeing is that there’s high species diversity in both urban and rural areas but generally more activity in rural areas, although there are some sites in the city that have a lot of activity. The species that we’re seeing include the big brown bat, little brown bat, and northern long-eared bat. These are all cave-hibernating species that are affected by white-nose syndrome. We’ve seen the populations of the little brown and northern long-eared decline quite a bit, and in fact the northern longeared was listed last year on the federal endangered species list. We’ve found them at a few of our sites; we’ll see what we find this year. Other species documented in Chicago are the evening bat, tricolored bat, silver-haired bat, and hoary bat. The Indiana bat is typically found in this region but hasn’t been documented by our team or others in many years.

When do you expect to have counts for this year?

We usually sit down and analyze all of our data over the winter, and it takes a while to go through all of the call files. We use software that helps us organize the data and gives general summaries of what we’re seeing.

Can you define a call file?

Each of our recordings is a call file. It can be up to two seconds long, which is long for a bat call. A bat call is very fast.

So the monitors start recording when the call starts?

Yes, they’re triggered by any ultrasonic noise in the environment. There’s a lot of mechanical noise in the environment that creates ultrasonic sound, but the software that we use removes it. The monitor records for two seconds at most, and then each recording is saved as an individual file on an SD card. We take the card back to the zoo, we upload all those call files, run them through the software that gets rid of any noise, and then we run them again through an auto ID system. This system reviews and compares every single one of these files to a reference library of calls of known bats that have been recorded all around the country.

The way the reference library is created is by capturing bats in mist nets, then releasing them and recording them as they fly away—so the species is known because it’s been in hand.

Have you participated in that process?

I have. I haven’t done it in Chicago, but I was part of a recording workshop in Kentucky a few years ago, which was great because Kentucky is the hibernating hot spot for bats in the Midwest. There are tons of bat species down there and a lot of activity, especially in the fall.

In Chicago, we’re using passive acoustic monitors because, as you can imagine, setting up nets all over the city and leaving them for multiple nights at each site is really labor-intensive. It also doesn’t guarantee that you’re getting an accurate picture of the maximum species diversity, because there are some species that might not fly low enough to get captured in a net. There are always individual bats that are trap shy and might be really good at avoiding the net, so you’re most likely to get a broader picture of species diversity when you’re using passive acoustic monitors—or at the least, with monitors you’ll be able to take a similar survey with a lot less work. But the data you’ll miss out on is that visual, individual demographic information, which is why the reference sound library is key.

Are you going to continue this study next year?

As long as we have funding and support we will continue to conduct the study. Next year, in fact, we plan to shift the focus a little bit to concentrate on the city and increase the distribution of our recording sites throughout the city.

What’s unique about this work is that no one has really studied bats in the city of Chicago. The most recent published study dates from the early 2000s, and it was mostly conducted out in forest preserves surrounding Cook and Kane Counties. Our study is therefore revealing a lot of interesting information about bats in cities that has never been available. What’s really exciting is that we’re part of a greater movement; there was a recent urban bat study in New York City and one in Los Angeles, so there’s definitely

Silver-Haired Bat

momentum for this type of research. That’s the next step of the work that we’re doing in Chicago—taking these methods and identifying partners in other cities who can then deploy the equipment and collect data in the same way at the same time.

Can you talk about the role that bats play in the environment? What role do they play in an ecosystem?

One of the largest roles that bats play is eating insects. It’s been estimated that they save three billion dollars for the agricultural industry each year in terms of natural pesticide, so without bats that would be a huge economic loss. It’s also a direct benefit that we can feel—sitting out at night in your backyard or in the park and not being constantly surrounded by mosquitoes. If you think it’s buggy right now, imagine what it would be like without bats!

What other insects do they like to eat? Are they picky eaters or are they broad eaters?

It varies by species. They eat mosquitoes, different fly species, moths—all kinds of insects. That’s a huge benefit. Other bat species are pollinators so they help propagate plants. One huge benefit they contribute to is tequila; bats are the main pollinator of agave plants. Many other agricultural industries like fruits benefit from bats as pollinators.

Are there any specific resources on our rooftop that would attract bats or be beneficial to them?

Having such a rich, diverse native plant community up there is going to attract insects and that’s going to attract bats. A conventional roof would have no value to them at all. We haven’t done an extensiveenough study comparing conventional versus green rooftops in Chicago, but I think that’s a direction we would go in the future. Research that has been conducted, certainly in New York City, has found a big difference in the diversity of species accessing green rooftops versus conventional rooftops.

Are bats generally found very high up? What range do they fly in?

That varies by species. There are some really high-flying bats like the hoary bat, although in the city, just to be able to navigate the urban landscape with all of its various building heights, they have to fly pretty high. But they’re also zipping down residential streets that have tree lines, using them as movement corridors and foraging along them. That’s also the height at which streetlights are found, which attract insects, so they can congregate there as well.

I think another benefit of a green roof in a city is that you’re providing bats with this really rich habitat that’s isolated from humans. It’s up high, it’s away from all the traffic and the cars and the human activity, it’s safe and quiet, and it’s at their flying height, so they can just dip in and forage and get out.

How adaptable are bats as a group? Would a species change its flying height from region to region for example? Can you think of instances in which a species becomes very habituated to an urban environment and changes their behavior; for instance, eating the insects that surround streetlights? That seems like a very city-centric behavior from what they would be doing otherwise.

As I mentioned, we have cave-dwelling and tree migrating bats. Tree migrating bats are not necessarily thought to be urban adapters; they’re thought to really need forests. But we’re seeing all of those species using the urban environment. So that could be telling us a couple things. They could be roosting in the city, which I think is very possible. They could be roosting in forest preserves that are just on the outskirts of the city and commuting in every night and foraging—some do have really big, long home ranges and they can easily move like that. It’s not a big deal for them to come

from a forest preserve on the outskirts of the city to forage downtown. I think they probably have more adaptability than we realize.

Interestingly, the cave-hibernating species are the most urban. They tend to be the more social species as well and they’ll form colonies in human-associated buildings. That’s why we’re really interested in sampling around the Studio, too, because there’s so many old buildings and church steeples and spots like that where they can roost without encountering much human activity. Cave-dwelling bats love old attics, garages, and barns. So those are the species that we were expecting to see in the city. Like the big brown bat, which is very common across the US. It’s often seen in cities and it’s pretty adaptable. But we’re also seeing tree migrating species. And we’re seeing them in the middle of the summer, which suggests that they’re not just passing through this area on their way to another place. They’re actually spending time here. We’re recording foraging calls from these species as well, so that’s also a good indicator. When you get a call that shows a feeding buzz—when they emit echolocation calls that get faster and faster so they can home in on the prey they’re trying to capture—you know that they’re foraging, which means they’re really spending time in the city.

Is it possible that the tree-dwelling bats are being pushed into the city from the agricultural areas as those are becoming more of a non-desirable versus acceptable habitat?

That’s a really good point and I think that’s a huge factor in the Midwest especially. The landscape surrounding Chicago is not a wilderness with abundant wildlife habitat. It’s intensively farmed. There’s hardly any continuous forests left; they’re all in these isolated patches. What’s interesting in the Midwest is that cities actually provide a lot of forest, especially in Chicago. There’s a lot of tree cover in cities, so they’re providing something that the surrounding rural area is not. To be able to take advantage of that, animals have to make some sacrifices and adjust to being around humans. There’s a lot of research that shows—not necessarily with bats, but say with coyotes in Chicago—that they shift their behavior to be more nocturnal so that they can avoid being around humans as much as possible. They’re also finding those natural areas, those little pockets of open space in the city. They’re figuring it out.

There’s a lot to look at, and what’s exciting is that urban wildlife ecology is an emerging field. Historically, people didn’t think of cities as being biodiverse at all; they thought they were wastelands in terms of animal life: the “concrete jungle.” Today, more and more people are starting to realize that not only are there a lot of species here, but cities can actually provide a lot of benefits to wildlife—they can be supportive habitats.

Is there anything people can do to help bats in urban environments?

Building bat houses is something that is really beneficial. It provides them with a safe roosting space. Especially if you have bats that are roosting in your building and you want to get rid of them—if you can work with professionals to extract them from the building and build a bat house for them nearby, you can continue to provide them with summer roosting habitat.

Other than that, just being aware of bats and their role in the greater environment is very important. At the Urban Wildlife Institute we always like to talk about the benefits of bats, why they aren’t scary and aren’t rats with wings, and how they’re actually crucial to our ecosystem.

One Chicago bat fact that I think is really cool is that the city is home to an urban-adapted taxonomic group. If you’re watching and paying attention when you’re out in the early evening, you can often glimpse them flying around. You just have look up at the lights and be aware. With

all urban wildlife and nature, there’s real benefits for humans. There’s so many opportunities to connect with nature right in the city—sometimes all it takes is remembering to look up.

Liza Lehrer is Assistant Director of the Urban Wildlife Institute at Lincoln Park Zoo in Chicago. She manages and collects data for the Institute’s field research projects, including the Urban Wildlife Biodiversity Monitoring project, and coleads the Bat Monitoring project.