Call of the Wild

Tell me about Wisconsin’s Baraboo Hills, where you live and work.

I grew up in the Baraboo Hills. There’s a long history of grassroots conservation here. Farmers, community members and Nature Conservancy staff worked parcel by parcel to piece together these big forest preserves that now we’re lucky to have. 

For me, it was a really intentional decision to study this place that I care so much about. Some collaborators and I started the Baraboo Hills Research Collective to do long-term ecological monitoring to understand how this ecosystem is changing and how we as land stewards and community members can ensure biodiversity here is able to persist. Our research has focused on oak woodlands, a fire-dependent habitat that used to be common in eastern North America. Oaks are keystone species—supporting an incredible diversity of wildlife. We’re losing these habitats, and a lot of the patches that are left are dependent on management that uses prescribed fire. 

Your research relies on traditional field methods like counting birds, as well as the newer science of bioacoustics. How does this newer technique fit in?

Bioacoustics uses sound recordings of ecosystems and habitats to learn something about the species that live there or to understand some kind of conservation problem. So we were looking at plant diversity, insect biomass, and the diversity and abundance of birds, doing all these detailed field measurements. At the same time, we were recording sounds—the bird and mammal and insect and frog species all calling—to see if there were some measure in the soundscape that would give us information about the ecology without having to go through and count or weigh every single species we’re interested in.

One index we look at is complexity. You can imagine going into a forest that has one or two bird species singing—the soundscape won’t be very complex. A place where there’s a dozen species singing will be much more complex.

Did you find any differences between managed and unmanaged habitats?

In managed oak woodlands, we found there is a higher richness and cover of [nonwoody plants] like grasses and wildflowers, a higher biomass of insects, greater populations of birds and more bird species overall than in unmanaged woodlands. And we were able to look at the soundscape and conclude that oak woodland restoration results in higher soundscape complexity and saturation.

What’s “saturation”?

It’s an acoustic index [developed by Zuzana Burivalova, one of Persche’s mentors] based on the acoustic niche hypothesis. The hypothesis says species that evolve together in an ecosystem all call at a different time or pitch, so their calls don’t overlap, and they can be heard above the background din. Like, if two frog species call at the same time, maybe one will have a high pitch, and one will have a low pitch. Or if they have the same pitch, they might call at different times of the day.

If you imagine going into a forest where every species is still present, every time of the day, nearly every acoustic pitch would be full—that would be a really saturated soundscape. But if you go to a place where there is a lot of hunting pressure or a lot of deforestation, there’d be gaps in the soundscape. It would be less saturated because you’d have a hole where a species used to be.

So listening to a forest can give us new insights into its biodiversity?

Yeah, bioacoustics is a great tool, especially for looking at cryptic species or remote landscapes. It’s an exciting time for this research. There have been some great advances in technology, so we’re able to ask more and more nuanced questions and do more complicated analyses over larger spaces and longer times. Right now, we’ve been collecting soundscapes at six locations in the Baraboo Hills continuously for an entire year [to really establish baselines for evidence-based conservation].

But for me, the significance of bioacoustics has to do less with the technology itself and more with what it’s accomplishing, which is helping us as humans be able to listen better and remember things—two things we’re not necessarily great at.

How so?

Bioacoustics lets us listen in on a single species or whole ecological communities. At the same time, we can archive sound recordings and return to them. Think of it like a time capsule that will continue to be useful long after we collect the data.