In most parts of the world, nature sounds like birds or insects—the cheerful, rhythmic chirps of a robin, say, or the hum of a cicada.
In Puerto Rico, it sounds like frog. Lots and lots of frogs.
If you take a walk in any forest on the island, you will hear a loud, almost deafening chorus of amphibians. The main singer is the common koki, a tanish tree frog with large, sticky toes. They are Puerto Rican icons no bigger than a ping-pong ball – CO-KEE, CO-KEE — To attract mates and mark their territory.
Puerto Rico, a Caribbean island and US territory, is home to more than 15 endemic species of frogs. And these animals have a lot to say. The number and diversity of frogs and their collective vocalizations can indicate the health of an ecosystem. Frogs, like other amphibians, are sensitive to subtle changes in climate and water quality, making them reliable environmental sensors, according to Marconi Campos-Cerquera, an ecologist.
When lots of frogs sing, it is a sign that the forest is healthy. A quiet forest is cause for concern.
Scientists are increasingly heeding their call. Over the past two decades, a large number of researchers have focused on bioacoustics, the study of all kinds of animal sounds, to monitor environmental health. It’s pretty simple: They put a few mics in the forest to collect sound, and then run the data they retrieve through computer software. That software reveals which animal species are there and when.
For several years now, scientists in Puerto Rico have been using bioacoustics to monitor environmental changes. By listening to frogs, they understand how climate change — and the storms and heat waves that come with it — is changing island life.
A frog’s paradise
On an overcast morning earlier this year, I drove into the mountains of central Puerto Rico with Chris Harmon, a scientist at WildMon, a nonprofit organization that monitors the health of ecosystems in Puerto Rico and elsewhere. Parts of the road had collapsed, possibly eroded by the excess rain. Climate change is making hurricanes more destructive –Including Hurricane MariaThat hit Puerto Rico in 2017 — in part loading them with more moisture.
Harman is parked on the edge of a meadow above the clouds. Before I opened the door I heard the frog singing. CO-KEE! CO-KEE! There were more occasional ones WHO-WHO-WHO-WHO-WHO From red-eyed koki, a small tree frog with rust-colored eyes.
“Frogs are ubiquitous,” Harmon said.
We headed into the jungle down a steep, overgrown path surrounded by ferns, palms and bromeliads (plants that look like the tops of pineapples). Harmon soon found what he was looking for: a microphone tied to the trunk of a large tree.
Housed in a simple black box, this mic records the sounds of the forest. It’s part of a long-term project started a few years ago by Rainforest Connection, another environmental group, to monitor Puerto Rico’s wildlife. There are 29 other mics like this in various habitats around the island that have been around for years.
The hardware is simple. The mic is connected to a circuit board and a battery that records one minute of sound every five minutes to a built-in memory card. Every few months, those cards are collected and the recordings are uploaded online and converted into spectrograms, which show sound data in visual form. Then, the software essentially scans the spectrograms for matches within an existing library of animal sounds. The data can tell researchers which species are present at each recording site and, more broadly, how the range of sounds in one habitat differs from another.
Mike Harmon showed me, at a site called Toro Negro, that has picked up various animal grunts over the past few years. These include those two noisy frogs, of course – the common and red-eyed coquis – as well as several other frogs, including melodious and grass coquis, which have their own distinctive songs. It also identified a variety of birds, such as the Puerto Rican toady, an emerald green species with a bright red throat. (The software that analyzed the sounds for the project only identified about 40 species of interest, Harmon said, including those that are threatened with extinction.)
Data is not perfect. Some animals, such as snakes, do not call at all. Also, sound alone can’t tell you much about abundance — that is, how many of a particular species is found in a given place.
“Determining whether 100 detected calls are from one bird during the mating season or dozens of less active individuals is challenging,” said Ben Gottesman, a bioacoustics expert at Cornell University. “Estimating population density through bioacoustics is still quite complex.”
But if your goal is to figure out which species live in or travel through a particular area, Harmon says, bioacoustic technology is hard to beat.
What this recorder taught us
At a basic level, microphones reveal what does and doesn’t work in a space without spending a lot of time doing field work. It helps scientists to map biodiversity easily. Local authorities and non-profits use these types of charts to establish new wildlife reserves.
But these words can help researchers understand how ecosystems are changing. A the pair of Study Based on bioacoustics, WildMon’s chief scientific officer Campos-Carqueira, who works with Harmon, found that several frog and bird species seem to be moving to higher altitudes, where it’s cooler, possibly due to rising temperatures. In the lowlands of the Luquillo Mountains, a rainforest in eastern Puerto Rico, for example, recording devices no longer detect the handful of frog species that once lived there.
“Many bird and frog species are changing their distribution on the island,” Campos-Cerquera told me. “Many species are going up [higher] Enter the mountains to track more favorable temperature and humidity conditions.”
This movement of frogs and birds makes existing protected areas less useful – because unlike the animals they protect, they are stuck in place. By mid-century, much of the habitat cool and wet enough for frogs will likely fall outside wildlife preserves. According to a 2021 Study led by Campos-Cerqueira.
Other studies have used mics to understand how superstorms affect island wildlife. inside Another 2021 studyScientists led by Gottesman compared bird and insect communities before and after Hurricane Maria using bioacoustics. Maria was the second strongest storm to hit Puerto Rico in recorded history, killing nearly 3,000 people and damaging or flattening millions of trees.
Although not so surprising, the authors found that sounds made by birds and insects (at least those that produce low and medium frequencies) dropped by about 50 percent after the hurricane. It took one to two months for insect noise to return to pre-storm levels, the authors found. Bird call diversity takes longer to recover.
According to the analysis, audio recorders detected a drop in bird calls two days before the storm hit, adding evidence that some animals — from warrior Near the shark – can detect the coming storm day in advance and flee the area. “In these times of rapid environmental change,” Gottesman and his coauthors write, “soundscapes can signal the ways in which changing disturbance regimes are transforming ecosystems.”
A new era of wildlife observation
Tropical ecosystems are complex. There are literally thousands of species of plants, animals and fungi that influence each other, like a complex mechanism that no one fully understands.
In just a few days in Puerto Rico this year, I saw boa constrictors and lizards and waterfowl, lots of weird bugs and lots of frogs. They all play a role, including the species we are only discovery
This complexity determines how ecosystems are changing—really, how we are Changing them is extremely difficult. And that makes it harder to hold those responsible for that change accountable.
Increasingly, major financial institutions, including Fidelity International, increasingly want to know the impact of their investments on the environment, and how declining ecosystems put those investments at risk. For example, how are insect pollinators working and what impact can they have on agricultural products and producers?
Advances in bioacoustics are making it easier to answer these kinds of questions. Along with motion sensing cameras, satellite images, and eDNA analysis, where scientists analyze bits of DNA in habitats — audio recordings and software to analyze them ushered in a new era of wildlife monitoring.
It’s not just about pointing out problems, like destroying a food web. It is also about helping to monitor the progress of nature restoration. a research Published last year inside nature communication, For example, showed that bioacoustics can be used to measure wildlife recovery in tropical forests that were previously cleared for cultivation and ranching.
Researchers analyzed audio from a forest in northwestern Ecuador, finding significant changes in communities of sound-making animals in forests at different stages of recovery. “Obviously regenerating forests are recovering species that are really found in old-growth forests, which is a really good sign,” study co-author Zuzana Burivalova told my colleague Byrd Pinkerton earlier this year. Episode of the podcast inexplicable.
The more time I spent in Puerto Rico, the more discerning my ears became. Not just recognizing “a frog”, I was able to identify different species of cocci, even when I couldn’t see them. (They were nearly impossible to spot, even when they seemed to be calling from mere inches away.) In those subtle musical differences I began to detect — in that diversity of frog croaks — the secret to the health of these forests. We just need to listen to unlock them.
