Prothonotary Warblers in Kansas Have a Secret. Can a Team of Volunteers Figure It Out?

Ann Tanner is running on four hours of sleep and showing no signs of it. On a humid June morning, she greets me with enthusiasm and a surprisingly strong handshake as I join a group of volunteers, gathered in a parking lot of Wyandotte County Lake Park in Kansas City, Kansas. Down the hill, a Prothonotary Warbler is busy defending his nesting territory, his sweet song punctuating the chorus of nearby birds.

As the president of Burroughs Audubon Society and a Johnson County K-State Extension Master Naturalist, Tanner has recruited the bird lovers and scientists here as part of a four-year quest to discover the migration route of Prothonotary Warblers in Kansas City. Last year, this team captured the warbler singing below us, named him “Hydrogen,” and fastened a geolocator to his back. In the 12 months since, Hydrogen flew to South America and back. Only he knows where exactly. What he doesn’t know is that the group milling around the parking lot is plotting to capture him today, and they will not give up until they’ve retrieved the precious data that he’s carrying on his little back.

The 15 members of today’s outing include Burroughs Audubon Society members and Johnson County Master Naturalists, retirees and young professionals, ornithologists and novice birders. All of them have played a role leading up to this morning. Once the necessary equipment—mist nets, a handmade Prothonotary Warbler decoy, and loudspeaker—is in place, the group steps about 30 feet away and Gabe McClain, a master’s student at Pittsburg State University in Kansas, begins playing Prothonotary Warbler songs on the speaker.

It doesn’t take long for Hydrogen to react. “I see him!” Tanner calls out after a couple minutes. A yellow speck begins chirping aggressively at the decoy from a branch above the net. He makes a swipe at his perceived intruder, flies into the net—and bounces out.

McClain continues to play the speaker. Another few minutes go by. He switches the recording to a different call, and then a bright flash of yellow flies into the net again. The group jumps with excitement and waits eagerly while McClain extracts the bird. He looks up, gives the group a sad smile, and shakes his head. It’s not Hydrogen; it’s his mate.

But Hydrogen soon reappears. A tense few minutes pass. Someone calls out, “Got the male!” McClain goes over to extract Hydrogen and says, to our relief, “Yep, he’s got his geolocator on.” McClain holds the brilliant yellow bird with a piercing black eye up to his fan club. Pointing to a small, rice-sized bulb on the bird’s rump, McClain says, “This little thing is what we’ve been after the whole time.” Working quickly to recover the precious data, a volunteer cuts the filament securing the geolocator to Hydrogen’s back, and soon McClain is holding the tiny tracker that holds the secrets of his migration.

Birders in the United States often associate Prothonotary Warblers with the dark swamps of the South. Kansas City roughly marks the westernmost edge of their range, but that may be changing. For at least the last four decades, Prothonotary Warblers have been shifting their range northwest. No one is sure why: It could be that hurricanes, drought, and wetland destruction are displacing them in the South—or it might be something else. The team assembled in Kansas City is part of an international effort to find out.

Erik Johnson, assistant professor of wildlife management at Louisiana State University and former director of conservation science for Audubon Delta, coordinates the Prothonotary Warbler Working Group, a consortium of federal and state agencies, NGOs, and universities that study the bird. They collaborate on large-scale studies to research fundamental questions about the species, like why the population is declining in some regions and increasing in others, how climate change is affecting their reproductive success, and whether their migratory flights intersect with offshore wind energy projects.

Currently, there are more questions than answers, especially around the western population. Although the western population is increasing, scientists know that the species as a whole is declining, but they don’t know what’s driving either trend, Johnson says. Mapping the migration of the western population could help explain its increase. Perhaps those birds are migrating to a different nonbreeding habitat, taking a less dangerous route to get there, or migrating when conditions are more favorable. “We don’t know that until we start exploring it,” Johnson says.

An opportunity came in 2023, when Johnson received a notably enthusiastic email from a birder in Kansas City. It was Tanner. She wanted to know how Burroughs Audubon Society and the Johnson County Master Naturalist Program could participate in the working group’s migration study. Tanner wasn’t a professional ornithologist like most of Johnson’s collaborators, but he didn’t have any migration data from Prothonotary Warblers breeding in Kansas. “And so I was like, ‘Oh, this is interesting. Yeah, let’s see where this goes,’” he says.

Jack Corrigan was the first Missouri Master Naturalist to volunteer with the Kansas City project and is now the Missouri lead. To better understand the Kansas City Prothonotaries, I join him for one of his nest box monitoring routes at Platte Falls Conservation Area, just outside Kansas City. We splash through a foot of water into the dark, sweet-smelling forest. It feels like a rainforest, and that’s probably why the swamp-loving warblers have chosen to nest here. I, too, would have been charmed, if it weren’t for the light rain of mosquitoes pelting my face and neck. Corrigan’s unfazed by the insect onslaught, but he still works quickly.

When we arrive at the first box, he gently knocks on it and a yellow blur shoots out. A female Prothonotary Warbler lands on a shrub nearby and starts calling in alarm. Corrigan opens the side of the box, revealing five grape-size white and brown eggs inside a nest of fine twigs and moss. He gently slides his phone over the nest, takes a photo, closes the box, and leaves.

Despite the protocol requiring nest checks only once a week, Corrigan repeats this process every three days. He says the chicks grow quickly and he could miss important developments if he came less often, but I suspect that he’s at least partly driven by his personal desire to see the birds and make sure they’re okay. He worries about chicks getting sick or eaten by predators, he says.

His fears are reasonable. According to Johnson, only about 40 percent of Prothonotary Warbler nests in natural cavities succeed in fledging at least one bird, primarily due to predation and Brown-headed Cowbird nest parasitism. Thanks to nest boxes that exclude cowbirds, predator guards, and a dedicated team of volunteers who monitor them, the Kansas City nest boxes have had a whopping 80 percent fledging rate.

While it may sound like a hobbyist’s craft project, building and installing nest boxes is a serious conservation tactic, says Johnson. “Predator-guarded boxes are very well documented to almost double the reproductive success,” he says. They’re so effective that they enable Prothonotary Warblers to breed in territories where they otherwise wouldn’t. “So you’re literally putting more babies into the world,” he says. 

For Corrigan, the study is an opportunity to help individual Prothonotary Warblers and the species as a whole. “You’re acting locally, but you’re affecting globally,” he tells me, after checking three more equally wet and buggy boxes. At home, he’ll upload his data to the project’s database, which sends the data to NestWatch, a program run by the Cornell Lab of Ornithology that compiles nesting data and makes them available to scientists, including the Prothonotary Warbler Working Group. With these data, scientists will be able to learn how Prothonotary Warblers’ reproductive success is changing over time, how it varies by geography, and how migration and nonbreeding habitat conditions affect it.

It’s one thing to know that you’re successfully hatching and fledging new birds, but a major question remained for Tanner: Where the heck were they going on their southbound migrations? Tanner had heard that scientists in the Prothonotary Warbler Working Group were using geolocators to answer this question in other states and she wanted the Kansas City crew to be a part of it. With guidance from Johnson, Burroughs Audubon Society purchased four geolocators for $250 each in 2024 and recruited Andrew George and Alice Boyle professors at Pittsburg State and Kansas State universities, respectively, to deploy them.

Kansas City was an ideal addition to the working group, not only because the birds there were unstudied, but also because of the local army of nest box volunteers. Each geolocator is valuable, so scientists only want to deploy them on birds that they have a good chance of recapturing. That means the birds need to survive a year, return to the same place, and be relocated. By installing predator-guarded nest boxes and locating nests, volunteers provide the locations where the scientists can reliably capture them. And by monitoring the boxes closely and removing threats, the volunteers increase the birds’ chances of surviving. George says he would not be able to put geolocators on the birds without the volunteers’ efforts.

In 2024, they put the geolocators on four Prothonotary Warblers nesting in their boxes. Scientists fasten geolocators to Prothonotaries with stretchable cord harnesses that don’t impede their movement. The Prothonotary Warbler Working Group found that harnessed geolocators weighing up to four percent of a Prothonotary’s weight had no detectable effects on their return rates. Despite these precautions, none of the four tagged warblers were relocated in 2025. Migration is a perilous journey, says Johnson, and only about 40 percent of Prothonotary Warblers are thought to survive the round trip. Undaunted, George and McClain placed new geolocators provided by the National Audubon Society on another six Prothonotary Warblers in 2025, including Hydrogen. A year later, on May 27, 2026, one of the volunteers spotted Hydrogen and his geolocator at Wyandotte County Lake.

A few days after Hydrogen was recaptured and his geolocator retrieved, George downloaded the geolocator data, which consisted of more than 100,000 pairs of solar radiation and barometric pressure values. The process of converting these to geocoordinates is “incredibly complicated,” he tells me. Late one night, after many hours of writing code, he produced the first migration map of a Prothonotary Warbler from Kansas.

On October 24, 2025, Hydrogen arrived in the Department of Bolivar in northern Colombia, 47 days and approximately 2,800 miles after leaving Wyandotte County Lake. For the next 168 days, Hydrogen likely lived in the Ciénaga Grande de Magangué, part of the Magdalena River Valley. The ciénaga is an area of vast flooded forests that is rich in wetland forest birds but being rapidly cleared for agriculture. On April 9, 2026, the urge to migrate once again compelled him, and he mostly retraced his path north, arriving at Wyandotte County Lake on May 3, 2026. On his northern journey, he flew 3,000 miles in just 24 days.

Hydrogen’s migration reveals the complexity of full life-cycle conservation. In 12 months, Hydrogen used habitat in five U.S. states, two Mexican states, two Honduran departments, two Nicaraguan departments, one Panamanian province, and one Colombian department. Prothonotary Warblers depend on people in all of them working together to conserve their habitat.

Kim Brand, Audubon’s managing director of community building, sees a role for Audubon’s community chapters in that. Last December, Audubon invited Burroughs to participate in a pilot program for migratory bird conservation. Audubon paired Burroughs with the Ciénaga de Mallorquín Ecopark in Barranquílla, Colombia, located in prime Prothonotary Warbler nonbreeding habitat. Through the ecopark, Barranquilla is advancing a model of ecotourism that integrates conservation, culture, and economic development. They do this by reinvesting funds in the local community, restoring mangroves, and involving local people in the creation of their programs.

“Beyond its conservation value, the ecopark is also helping improve quality of life in Barranquilla by bringing people closer to nature and strengthening the city's identity as a place that values and protects birds,” says Camilo Cardozo, Colombia country director for Audubon. The ecopark offers an important example of equity in urban conservation by engaging vulnerable communities, school students, and citizens from across the city in a public space dedicated to nature and bird conservation, he adds.

The partnership is currently in its early stage, but Tanner says she hopes Burroughs can work with the ecopark to create more awareness for Prothonotary Warblers in Barranquilla and explore future collaborative monitoring opportunities.

“I think projects like this give people hope,” says Brand. “And hope is what fuels action.”

After releasing Hydrogen, the team packs up the net and caravans to another part of the lake to recapture one other Prothonotary Warbler who returned with a geolocator, named “The Dude.” Although they already have Hydrogen’s geolocator, Hydrogen is just one bird among many. Collecting more migration data is vital for building an accurate understanding of the population’s migration.

This would be The Dude’s third time being caught: He was caught two years ago as a young bird but was too small to carry a geolocator, then caught again last year when he was bigger and got his geolocator backpack. Tricking him a third time could be quite challenging. The banders set up two nets and a decoy. After several minutes, The Dude appears carrying a green caterpillar, but he seems to have learned from his past mistakes. For nearly an hour, The Dude flutters above and around the nets but stays well clear of them. “Come on, just go in,” says Sara Blunk, a Burroughs board member.

Eventually, McClain and George run out of tricks and decide it best to come back later. “I think for my own sanity it would be good for me to catch another bird,” says McClain. We drive to a couple other nest boxes, tag a few more birds—including one who we learn is one of The Dude’s chicks from last year—and return to The Dude’s nest one hour later. The banders set up all three of their nets and two decoys. They return to our observation spot sweating, panting, and with a slightly delirious look in their eyes.

It’s now 4:15 p.m. We’ve been at the park since 9:00 a.m. It’s hot and humid and every inch of my skin is covered in a thin layer of sweat. My back hurts from standing for hours, but Tanner tells me that the grass probably has biting mites, so I can’t sit. (It turns out the mites got me anyways). Some of the volunteers have gone home, but five are still here. I ask them why.

Megan Summers, who took time off from work to be here, says it’s the joy of seeing other people experience something they’ve invested so much in. Heather Cwach, a Master Naturalist who helped start the nest box program, says she wants to see the validation of their efforts. Tanner sums it up: “That bird carries our heart in that GPS.”

So we wait for another long, sweaty hour as George and McClain try every trick they can think of. Finally, they disappear behind bushes to check a net for the hundredth time and go quiet. One of the volunteers goes to look and returns pumping her fist. There’s a Prothonotary Warbler in the net! George and McClain have started removing the bird, but we haven’t heard any shouts of joy. The volunteers gather next to the net to anxiously watch. McClain confirms that the bird is The Dude, but McClain doesn’t look happy. Finally, he gives us the bad news: The geolocator is gone.

Tanner’s smile melts and her eyes go wide. She stands frozen with her mouth agape for several seconds, and then she gives a resigned smile. What else can she do? McClain carries The Dude back to the banding station, looking at him with profound disappointment, as if he’s been tricked. Knowing full well that it will be even harder to capture him a fourth time, the group collectively decides to put another geolocator on The Dude. They take his measurements and send him back to his chicks.

Tanner has had many years to brace herself for disappointments like this. “Trying to catch this bird is not for the faint of heart, because you know you’re going to fail more than you’re going to succeed,” she tells me. She knows how unlikely it is for a 14-gram bird to fly to Colombia and back. Doing this work requires a tremendous amount of hope, she says, and recapturing Hydrogen’s geolocator is more than she could have hoped for.

“It’s a miracle,” she says, “And I can’t wait to see what his data show.”

With that sense of wonder, this team of bird lovers has come so far, and their work is only just beginning. Throughout the summer, George and McClain deployed 36 geolocators on Prothonotary Warblers in eastern Kansas. There may be many more miracles to come.