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At Duke Farms, we believe the natural world speaks volumes if you know how to listen. One of the innovative tools we use to understand the health of our ecosystems is bioacoustics monitoring, a method that allows us to “hear” the environment through science. 

Bioacoustics is the study of sounds produced by living organisms. From the chorus of spring peepers (Pseudacris crucifer) in a wetland to the drumming of a Red-bellied woodpecker (Melanerpes carolinus) deep in the forest. At Duke Farms, we use small recorders to collect data across our diverse habitats. We use autonomous recording units (ARUs), which provide a long-term record of ecological change, helping us make data-informed decisions about land stewardship practices and habitat restoration. ARUs are considered a non-invasive way to observe wildlife occurrences.  It enables us to detect elusive or nocturnal species that visual surveys might miss, and record for days at a time.  Meaning, a lot more data without the bias of a surveyor's disturbance when collecting data in the field.  

But how does it actually work? 

Our conservation team carefully installs ARUs in key habitats like wetlands, grasslands, and forests. These devices can record for weeks or months at a time, storing hundreds of hours of audio. We aim to understand how our restoration and land management practices are impacting biodiversity, Lessons learned can help us improve our methods and find new, innovative ways to enhance the quality of wildlife habitats and restore native species. Once collected, the recordings are downloaded and analyzed using specialized software that visually maps the audio into spectrograms—a kind of visual fingerprint of the sounds. From there, trained team members and bioacoustics partners use pattern recognition, call libraries, and sometimes AI-assisted tools to identify species-specific vocalizations. Think of it as decoding a secret language of the wild, or Shazam for wildlife.  

This process helps us track indicator species—wildlife whose presence signals environmental quality or change. The call of a bobolink (Dolichonyx oryzivorus) or eastern meadowlark (Sturnella magna) might tell us a grassland restoration is succeeding, while the seasonal song of the wood thrush (Hylocichla mustelina) offers insight into forest health. Bobolinks and eastern meadowlarks are grassland obligates, they require large, open fields of native grasses for nesting and foraging, making them especially vulnerable to habitat loss and fragmentation. Both species have experienced steep population declines across their range, and in New Jersey, they are considered species of special conservation concern due to the rapid disappearance of grassland habitat. Similarly, the wood thrush depends on mature deciduous forests with rich understory layers. It has declined significantly due to forest fragmentation and habitat degradation and is also listed as a species of concern in the state. 

By monitoring these vocal indicators, we gain crucial insight into the effectiveness of our land management efforts and the broader ecological integrity of our landscapes. As we continue to innovate in how we care for this living landscape, bioacoustics has become one of the most exciting tools in our conservation toolbox—one that reminds us that every chirp, croak, buzz, and birdsong is a signal worth tuning into. 

Examples of Bioacoustic Projects at Duke Farms 

Grassland birds in restored grasslands 

One of our key bioacoustic monitoring projects focuses on assessing grassland bird populations in our restored meadows and grazing pastures. These grasslands are part of a long-term effort to enhance native biodiversity while integrating regenerative agricultural practices and reseeing parcels of land with native grass mixes. By deploying ARUs across sites with different grazing regimes and reseeding efforts, we’re able to capture breeding-season vocalizations from key indicator species like bobolinks, eastern Meadowlarks, and grasshopper sparrows (Ammodramus savannarum). Comparing these acoustic datasets helps us understand how varying grazing intensity affects bird presence, spatial activity and timing, offering a unique window into how working lands can support both agriculture and biodiversity. These insights guide how we manage grazing rotation and native grassland restoration to benefit both birds and soil health. 

Duke Farms’ Raritan Reforestation Project 

Another application of bioacoustics is in our Raritan River Reforestation site, where decades of ecological degradation are being reversed through a multi-year forest restoration effort. Here, ARUs are placed strategically among young forest plots, monitoring how returning tree cover is influencing habitat suitability for birds and bats. The devices capture the calls of forest-dwelling birds like the Wood Thrush, Eastern Wood-Peewee, Scarlet Tanager, and Yellow-throated Warbler - species that thrive in maturing woodlands.  

At night, ultrasonic microphones record the high-frequency echolocation calls of foraging bats, allowing us to track the return of these important insectivores. These soundscapes give us critical feedback on how effective our restoration work is at rebuilding complex, layered habitats that support a rich community of wildlife. 

Through projects like these, bioacoustics is helping Duke Farms move beyond snapshots of biodiversity toward a more nuanced, temporal understanding of ecosystem recovery.  

Experience the Sounds of Nature at Duke Farms

You don’t have to be in the forest or meadow to hear what nature has to say. At Duke Farms, our bioacoustics monitoring program captures the wild soundscapes of New Jersey—from the bubbling calls of spring peepers to the melodic song of the wood thrush.

Now, you can listen in from anywhere. Whether you're relaxing at home, working, or looking to reconnect with the rhythms of the natural world, our archived recordings and sound clips let you experience biodiversity in real time.

Tune in, slow down, and hear what the land is telling us.

The nest sits empty this morning, and the woods are missing a certain sound. The woodpeckers, blue jays, and so many other birds continue to call. At other times it is eerily quiet. All the eaglets are no longer nestlings. They have all graduated to fledglings or juvenile bald eagles. 

During this first year, still sporting their dark brown feathers they will be called juveniles. Once they reach 1 year old and have molted those feathers, they will be immature or sub-adult bald eagles. A bald eagle goes through many color changes in the first 5 years of life. Several groups have interesting articles about their growth and color changes.

Avian Report Indiana Nature Resources Foundation  

H58, the first to hatch, was the first to fly. She fledged on May 17th. She flew off with the confidence she has shown all season with each milestone reached.

H57, the youngest eaglet in the nest, fledged next by necessity on May 23rd. He was practicing his branching and fell when a gust of wind hit him causing him to slip off the branch. He landed on a branch below, and could then be seen flying away.  He flew by the nest about 5pm, almost landing on his sibling’s back before flying into the branches nearby. 

H59, the middle hatch, was the last to fly. She (most likely a female looking at her size now, though her measurements were not conclusive at banding) watched both her siblings, practiced wing flapping and jumping, and achieved great height, but hesitated. 

Finally in the early morning hours of May 26th, she took off from the high perch. 

The quiet of that morning did not last long. The female flew into the nest, delivering breakfast. Two fledglings followed with much noise and wings flapping. 

H58 was hungry this morning, and let her brother know in no uncertain terms this meal belonged to her. He managed a couple steals but not much.

When eating was complete, up the branch they went, taking up old positions. Calls continued to ring out. One came from H57, who was sitting on the branch below his big sister, H58. Another came from a short distance away. H59? Most likely. Having worked up the confidence to fly, she will need it again to leave whatever branch on which she is perched.

They remained on the branch for some time before flying off. H57 was the first to go.

H58 followed a few minutes later.

Bird songs continue to fill the air, even the occasional eagle’s call as the  morning rolled on. Prey came into the nest again in the early afternoon, and all 3 fledglings came home. They took turns eating and trying to steal. At the end H58 got her fill while her siblings sat together on the branch.

H59 and H57 sat together back on the branch on the afternoon of H59’s first flight. Sometimes, they talked to their sister who was out of cam view. An adult joined in the chorus at one point before they all settled down. Now that everyone is flying we will see less of them as May gives way to June. Eagle cries once heard frequently in the woods will go silent, as the other birds who share this habitat, fill the silence with their songs.

Viewers will enjoy the visits we still will have before the young eagles disperse from the area. We will watch as they become stronger and more graceful fliers.

Since fledge day, H58 has been back to the nest. She mostly returns when prey has been delivered, right on time for a free meal. While perched on the high branch on the morning of May 19th, viewers were treated to another close look of H58.

Perched just under her was her little brother, H57.

H59 rested in the nest alone.

That evening, H58 slept on the high branch. H57 spent time sleeping on the mid branch. H59 had the nest.

May 20th, H58 was back and forth to the nest tree. She did spend much time perched with her siblings.

H59 is right up there on the branch with siblings. Confidence is slowly building in this one.

With 3 big eaglets sharing 1 branch, moving around siblings is tricky. Watching a game of leapfrog, a watcher must be fearless. So must the eaglets. Dig in your talons and duck when big sister comes flying over your head!

Sticking landings for a new fledgling can be tricky too. H58 found that out the hard way the morning of May 21. She came flying into the crowded nest fast! Since both siblings were there, landing space was limited. 

She couldn’t stop, and overshot the nest. She tried to hold onto the branches of the nest.

She lost her grip, and gravity took over. She flapped hard as she fell through the leaves and branches of the nest tree, her siblings looked on. 

The forest under the nest tree is full of saplings and many other plants. Hopefully she had a soft landing. Viewers held their breath all day. Was she OK? H57 and H59 looked for their missing sister too.

Later that morning both adults brought prey to the nest. A feeding frenzy ensued.

At one point the female called out. Was that an invitation for H58 to get up and join the family? 

H58 never did show up at the nest for lunch. H57 and H59 ate their fill.

Soon after the adults left, all got quiet. Everyone waited and wondered what happened to H58. Just before 6pm, dinner was delivered. H57 flew down and laid claim to it.

H59 joined the feast. Then to everyone’s surprise, and relief to viewers, H58 flew down to join the family for dinner. 

Eating her fill, and having a full crop she flew up to the branch.

She hesitated for just a bit, then took off, looking strong.

The eaglets were in for another wet day. As the rain continued to fall, H57 and H59 sat together on the branch. Distant eagle calls could be heard. Parents? H58? The siblings practiced their wing flapping and moving on the branch. H59 took a slip, but caught herself and held on. 

H59 finally made it to the top perch and sat with her brother.

When food is around, look for H58 to come home.

After all the eaglets had their fill, they sat together on the branch.

This afternoon, the cam panned the area. H58 was not seen, but it sounded like she was near. H59 and H57 were on the branch flapping together when they heard the cam. It does make a slight noise as it is moved. They stopped flapping to take a look, but soon ignored it.

They have all grown into beautiful birds. Over the next 5 years, their feathers will slowly change to show a bright white head and tail. The bill, now dark, will also slowly change to yellow.

Young eagles are curious and will play with things in and around the nest. Sticks are moved around, and turtle shells (in past years) are explored. Branches and leaves of the nest tree are also something to check out. H59 did just that this afternoon. 

The nest is not empty yet. Viewers have plenty of action yet to observe. H57 and H59 are just turning 12 weeks old. H58 will continue to fly and return home. She may also be off cam view, perched in another tree calling for her siblings to join her. Have your volume up to listen for her. Watch for her siblings to react. H57 looks like he wants to go but H59 is still hesitant. Is he waiting for her? Will they fledge together? We all keep watching.

May 17th was an action packed day! The last update was practically old news as it was shared. 

Bald eaglets can fledge as early as 12 weeks. A fledge is when the eaglet leaves, not only the nest, but the nest tree itself. Many eaglets do return to the nest, mostly following an adult with prey. They may return to sleep at night, or not. Parents will continue lessons for survival. A fledgling will need to learn how to hunt and eat prey out of the nest. By the end of July or beginning of August, the eaglets from this nest will most likely leave their family and begin life on their own.

Today’s big news in case you missed it, is that H58 has fledged 3 days ahead of her 12 weeks hatch date. She had been very active branching in the days leading up to her first flight away from the nest tree. On May 16th, H58 pushed higher and higher on the branch until she went as far as she could on that branch.

H58 really tested her skills as she turned and leaped from her perch.

H58 flapped her wings and continued down to the nest.

While perched at the top of the branch, viewers were treated to nice close up views of H58. 

H58 has reached the milestone of sleeping on the branch. She slept up there for the last 2 nights, coming down in the wee hours of May 17.

Early in the morning of May 17, H57 and H59 were on the nest “beaking”. Birds touch beaks as a way to clean each other’s beak. While her siblings were busy, H58 had other things on her mind. 

H58 worked her way up to the top perch of the branch. Something had her attention as she kept looking around. Was an adult perched nearby, encouraging her to fly? She crouched as her siblings looked on…

…and off she flew!

Last year before both eaglets fledged, they flew to another branch in the nest tree that was out of cam view. Did H58 do the same, or had she truely fledged? I could hear eagle calls mixed with those of the turkeys. Each time, her siblings looked toward the sounds. Was that H58?

H57 and H59 took turns flapping and jumping. Did they want to follow their sister? A little over an hour later, breakfast arrived! H57 almost got knocked off the branch. Thankfully all was well, and both H57 and H59 ate.

Eagle calls stopped once the adult flew off and left the 2 eaglets to feed. Thankfully the cam operator began to pan, searching the area for H58. She was gone! H58 fledged this morning May 17, 2025, just shy of her week 12 hatch date.

H59 and H57 remain in the nest for now. How soon before they go, and who will it be? 

H59 is older, and suspected to be female. Will the younger brother, H57 fledge first? He wasted no time in hopping up to the knot of the branch and back down again. 

H59 is not out on the branch, but sure catches lots of air during those flapping exercises!

H57 continued to reach a higher perch on the branch as the morning went on. He is looking relaxed on his perch as he dangles 1 foot over the edge. H59 watches and takes note.

Fish was delivered to the nest several times throughout the day. H57 and H59 wait for the next one.

Late in the afternoon, H57 and H59 see something coming.

H58 finally makes an appearance. Her landing was a bit fast, but she pulled up to stop just fine. Those landings will improve with practice. Landings of newly fledged bald eagles can be clumsy. She did just fine.

About an hour after her arrival, H58 was just in time for dinner. The female arrived with a nice fish.

H58 came down from the high perch in record time.

H58 was her same old self, pushing her way to steal the prey, and eat. 

The 3 eaglets took their positions on the branch and nest. H58 is at the top in her favorite spot. H57 is on the knot. H59 is in the nest, but shows off her wings.

Who will be next to fledge? How long will H58 continue to visit the nest and her siblings? She will come and go, as will her siblings when they fledge until the time comes to go out on their own. Viewers, stay tuned to the cam. What an exciting day, and there’s so much more to come!