Wild With Nature

July 9, 2025, Highwood Creek, Chouteau County, Montana. I hear it as soon as I step out of the car, that resonant, knocking cucucu that I’ve been listening for all across Montana this summer. Black-billed cuckoo (Coccyzus erythropthalmus)! My hands are shaking and my heart is thumping as I start recording with my phone, just in case the cuckoo doesn’t sing for very long. I hurry to pull my parabolic recorder out of the car, turn it on, waste precious seconds debating whether to bother with the headphones. I slip one headphone on, aim the parabola, and press record. The cuckoo keeps singing.

The wild red raspberries (Rubus idaeus) are ripe along Highwood Creek and the fireweed (Chamerion angustifolium) is blooming. The cuckoo is singing from a patch of cottonwood gallery forest sandwiched between the creek, the gravel county road, and a driveway. I walk a bit closer along the road. The singing stops. A slender bird with a long tail and a very white belly sails across the driveway and disappears into a dense clump of chokecherries.

Somewhere among the forest

The cuckoo sings again from the chokecherries (Prunus virginiana), cucucu, cucucu, rhythmic and soothing. A minute or two later, I hear it again farther downstream. It must have slipped out of the chokecherries without me noticing. 

Then it falls silent. I wait 15 minutes. Nothing. Only the song of a black-headed grosbeak (Pheucticus melanocephalus) fills the cottonwoods. But the cuckoo is out there, somewhere, a silent shadow among the shrubs. The memory of its voice reverberates in my body: a mystery. A reminder. A call to understand. There is more going on in this changeable forest than we can possibly know.

It was music that brought Anna Kurtin to the cuckoos—music and a curiosity about secretive wildlife. After a childhood near Austin, Texas and a biology degree at the University of Texas at Austin, she began working for the National Park Service in Arizona studying bats and spotted owls. The challenge of finding these elusive animals and a childhood love of music—playing percussion, specifically—came together to draw her deeper into acoustic methods of monitoring mysterious wildlife. And in 2022 this interest brought her to the University of Montana, where a team of biologists and conservationists had already begun to coalesce around black-billed cuckoos and was seeking a graduate student. 

July silence

In Montana there’s a long time in the July night when the cottonwood forest is nearly silent. Nobody sings; only the faint burbling of the water ripples the stillness. Perhaps a fledgling great horned owl (Bubo virginianus) screeches once in a while. And amid the silence, if you’re lucky, you might hear the croaking flight call of a black-billed cuckoo passing by overhead. In some parts of the breeding range, observers have heard as many as six cuckoos flying past in the night, making these calls. Why do they do this? We still don’t know. Are they venturing forth to forage, heading out to feed on caterpillars in the dark? Sometimes people also hear cuckoos singing during the night, that distinctive cucucu ringing out from the depths of the forest.

If only we could be in multiple places at once, listening night and day for the sound of a cuckoo. Perhaps then we could begin to answer some of the many mysteries about these birds. But there was a way to do this, it turned out, a device known as an autonomous recording unit (ARU). An ARU is simply a battery-powered microphone with a memory card. By placing ARUs along eastern Montana’s river valleys, Anna’s team hoped to be able to find more cuckoos.

In search of black-billed cuckoos

In 2022 and 2023, Anna and her collaborators—Dr. Erim Gómez and the Charismatic Minifauna Lab at the University of Montana, Anna Noson and the University of Montana Bird Ecology Lab, Dr. Andy Boyce and the Smithsonian Migratory Bird Center, and biologists at Montana Fish, Wildlife, and Parks and Montana Audubon—set out ARUs in a variety of habitats along the Missouri, Musselshell, and Yellowstone Rivers. These general areas were already known from previous sightings and habitat modeling as some of the best in Montana for black-billed cuckoos. But the team wanted to gain a finer-scale understanding of where cuckoos were, where they weren’t, and why.

They programmed each ARU to record sounds for four half-hour blocks each day, two at night and two during the morning. (If they had left the units running 24/7, they would have rapidly depleted the batteries and memory cards.) They left recorders out from early to late summer to capture the black-billed cuckoo breeding period.

38,000 hours

Two seasons of the constantly-changing music of the cottonwood forest elapsed. Yellow-breasted chats (Icteria virens) sang, and orchard orioles (Icterus spurius). Great horned owls hooted in the night. July brought an emergence of hungry baby birds, and a flood of fledgling northern house wrens (Troglodytes aedon) begged harshly. The battery-powered microphones flicked on and off, logging it all in half-hour snapshots. In all, over 38,000 hours of audio. And somewhere within those thousands and thousands of hours, perhaps, were the songs and flight calls of black-billed cuckoos.

Now came the many months of intensive computer work. Developing a machine-learning algorithm with collaborators from the Kitzes Lab at the University of Pittsburgh to sort out cuckoo sounds from everything else. Listening to countless hours of audio to test the algorithm. Compiling habitat data the team had collected in the field. Building statistical models to account for factors such as background sound, vegetation density, and time of year that might affect cuckoo detections. More models to characterize the habitats where cuckoos called and whether the same habitat factors also correlated with frequency of calling. All of the quiet, painstaking, methodical work of a Master’s project.

Finding Montana’s black-billed cuckoos

At last, the results. Of the 41 sites where Anna and her team placed ARUs in 2022—all of them spots where cuckoos had been observed in previous years—they documented black-billed cuckoos at 12. In 2023, they expanded their sampling to 107 sites, including both known cuckoo spots from previous years and never-before-surveyed sites spread across multiple habitats within the same river valleys. That year, they found cuckoos at 20 of 107 sites. 

In 2022, Anna and her team fine-tuned when to set out ARUs and when to pick them up to capture a full cuckoo breeding season. 2023 gave them this full seasonal picture—and they found that calling activity varied strongly throughout the summer. Black-billed cuckoos called relatively frequently throughout June and the first half of July, during the day and less frequently at night. But after July 18, calling activity declined precipitously. If 2023 was at all representative, it would seem that the chances of hearing a cuckoo in Montana after mid-July become very slim. 

Modeling cuckoo habitat

The habitat models added more detail to previous notions of what an “ideal” black-billed cuckoo habitat might look along eastern Montana’s rivers. To find a place that might be good for cuckoos: Look for landscapes where the river’s-edge forest canopy is extensive—landscapes, perhaps, where the cottonwoods (Populus spp.), willows (Salix spp.), and green ashes (Fraxinus pennsylvanica) stretch for miles. As you walk across this landscape, look for patches hundreds of yards wide where there’s lots of variation in the canopy height of the forest, where old trees and younger ones mix.

Search for spots where there are tall shrubs like chokecherries in the understory. Stay away from places where the conifers intrude and avoid areas close to the river crowded with single-age stands of young cottonwood and willow saplings. Instead, look for patches with lots of vertical complexity: areas where younger and older trees mix, creating a more variable canopy. And maybe, just maybe, you’ll hear a cuckoo.

Return to the Marias River

July 6, 2025. In three more days I’ll get to hear the black-billed cuckoo along Highwood Creek, but I still have no clue of that. This evening I’ve returned to the Marias River where I listened for cuckoos in early June, the patch where Anna Fasoli heard them singing in 2021. Common nighthawks (Chordeiles minor) peent in the gathering darkness as I hike down to the river and pitch my tent near the cottonwoods. But then the night deepens into that July silence. No cuckoo song reaches my ears, no croaking flight call. No black-billed cuckoo wakes me from my dreams.

I get up in the morning to the shrill calls of a family group of American kestrels (Falco sparverius) as the sun lights up the trees. An adult brown thrasher (Toxostoma rufum) feeds a begging juvenile, then launches into an extended bout of song. A flood of young northern house wrens begs from the forest undergrowth. The brown thrasher keeps singing for a long time—loudly—though I didn’t hear him at all last month. Will I have the same luck with a cuckoo? But as I wander around in this constantly-changing forest, neither a croak nor a cucucu reaches my ears. 

When we don’t find cuckoos

If I could convert myself into a sound recorder and stay here for weeks or months, would I finally hear a cuckoo? Or is this extensive cottonwood forest like most of Anna Kurtin’s 2022 sites: a place that had cuckoos in a past year, a place where the habitat seems okay, but with no cuckoos now?

Anna points out how variable these birds can be from year to year, or even within a single summer. There’s the research of Claire Johnson and Thomas Benson in Illinois, which strongly suggests that black-billed cuckoos can move widely even within a single breeding season. All of it highlights that for a species so secretive and so mobile, even answering a simple question like “where are the cuckoos?” is incredibly difficult.

Fall migration

We don’t know exactly when black-billed cuckoos leave Montana in the fall. Across the breeding range, sightings diminish markedly between August and September. Migrating at night, they join a tide of birds in motion, a nocturnal wave headed south. They pass by almost unnoticed, guided by the stars. An invisible marathon through dark skies, a lonely flight call over the sleeping earth.

By the end of September they start arriving in parts of Honduras and Nicaragua, where the Middle American screech-owls (Megascops guatemalae) trill at dawn. They keep advancing southward and make it to Colombia, Ecuador, the Amazon region of Peru and Bolivia. And then they almost disappear. For the three months between December and February, all that we know about black-billed cuckoos comes from a few dozen observations. Even where they are in this season is rather a mystery—let alone what they’re doing, what their lives are like in this vast, biodiverse region. And if it’s hard to study such a secretive bird in June and July, it’s even harder in January, when the cuckoos are silent. 

Black-billed cuckoos across the Americas

But here, too, are people who fall in love with the cuckoos and try to understand them. During the Covid pandemic, a team of researchers at SELVA, a Colombian non-profit dedicated to conservation in the Neotropics, began a study of black-billed cuckoos. The team carried out cuckoo censuses in Ecuador and identified an important region for nonbreeding cuckoos in El Oro Province, in southern Ecuador. They also fitted three cuckoos in Colombia with radio transmitters, hoping to learn more about their migratory paths using the international Motus network of radio receivers.

Although two of the cuckoos with radio transmitters disappeared without a further trace, one of them later showed up in North America, pinging Motus towers near Lake Erie and Lake Ontario. But sadly, the project’s funding did not continue. The biology of the black-billed cuckoo remains little-known in this region; but the team from SELVA is determined to find a way to continue with this research in the near future. 

The more that I learn about black-billed cuckoos, the more they fascinate me. A migration in the dark; a silent and little-known life in the tropical forest; a population decline that we still don’t understand well. Waiting in the silence of the July night among Montana’s cottonwoods, almost without breathing, waiting for the voice of a cuckoo. You might hear it, but most likely you won’t. And among all of the unknowns, a network of people, from Montana and Illinois to Colombia and Ecuador, who join together to try to understand cuckoos and help them. 

Afterword

Something that I find very striking about black-billed cuckoos is the degree of collaboration they seem to inspire. Many thanks to Anna Kurtin and Dr. Camila Gómez (SELVA) for their participation in this story, and to their research teams for all of their contributions to our understanding of cuckoos. To learn more about all of the ongoing research and conservation projects at SELVA and to support this important work, visit https://www.selva.org.co/. Thanks to Harriet Marble for telling me about a possible black-billed cuckoo report near the Highwood Mountains, which finally allowed me to observe one! Finally, thanks to Tim Spahr for his permission to include his black-billed cuckoo song and flight call recordings in the podcast, and to Ian van Coller, Bo Crees, and Peter Dudley for letting me include their photos (one of Bo’s photos is also featured in this page’s banner).

Further reading

Hughes, J.M. (2020). Black-billed cuckoo (Coccyzus erythropthalmus), version 1.0. In Birds of the World (A.F. Poole, editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://birdsoftheworld.org/bow/species/bkbcuc/cur/introduction

Johnson, C.A. (2021). Detection, habitat use, and occupancy dynamics of black-billed cuckoos and yellow-billed cuckoos in Illinois. M.Sc. thesis. Urbana, IL: University of Illinois Urbana-Champaign. https://www.ideals.illinois.edu/items/118405

Johnson, C.A. & Benson, T.J. (2022). Dynamic occupancy models reveal black-billed and yellow-billed cuckoos have high rates of turnover during the breeding season. Ornithological Applications 124(3): duac021. https://doi.org/10.1093/ornithapp/duac021

Kurtin, A.M. (2025). Comparing survey methods and investigating habitat use of black-billed cuckoos (Coccyzus erythropthalmus) in the Northern Great Plains. M.Sc. thesis. Missoula, MT: University of Montana. https://scholarworks.umt.edu/etd/12436/

Marks, J.S., Hendricks, P. & Casey, D. (2016). Birds of Montana. Arrington, VA: Buteo Books.