July 26, 2023
The morning sun paints the rocky summits of the Teton Mountains in pink and blue as we set up the nets. The meshes of black nylon hang nearly invisible, each one suspended in a vertical sheet between two metal poles. It looks almost as if we’re getting ready to play badminton in the middle of the forest. But these nets are taller, more specialized—and highly regulated under federal and state permits. Known as “mist nets,” they have nothing to do with athletics—and everything to do with our understanding of the songbirds around us.
By the time we’ve set up the nets, the sun is sending golden light through the tops of the cottonwoods along the stream. A warbling vireo sings from high in the canopy, and violet-green swallows are catching insects in the airspace above us. This morning we’re at the edge of Grand Teton National Park, 18 miles northeast of Jackson, Wyoming. Around us is a diverse mix of habitats that supports dozens of species of breeding birds.
A diversity of birds
There are dense stands of aspens where the northern flickers and red-naped sapsuckers nest. At the edge of the aspens are several log buildings, managed by Teton Science Schools for their educational programs. Meadows of aromatic sagebrush, where the Brewer’s sparrows sang in June, are now speckled with the yellow blooms of little sunflower (Helianthella sp.). Cottonwoods and blue spruces form a tall forest along the creek, where a few white-crowned sparrows are chipping. Nearby, several beaver ponds spread out among the willows, and a spotted sandpiper flushes suddenly from the shoreline.
In a place like this, there’s quite a lot that a trained naturalist can learn about the birds through careful observation and listening. By visiting repeatedly throughout the year, we might begin to understand the seasonal rhythms of this place: which birds pass through only in migration, which ones stay for the summer. We could learn where the cliff swallows build their mud nests under the eaves of the buildings—and even find the boundaries between warbling vireo nesting territories in the aspens.
But at some point, we would start bumping up against questions that we’re powerless to answer through passive observation alone. How many of the songbirds that breed here actually survive all of the perils of migration and return again next summer? Are many baby birds fledging, or just a few? How are the birds actually faring here, and how does that compare with other areas?
These questions aren’t matters of idle speculation. We live in a world in which the human presence is palpable everywhere, from the Arctic to the Amazon. Questions such as these go beyond the patterns we can observe visually to help us understand when birds are prospering, when they’re struggling, and how many of them return next year. For bird conservation, these topics are critical.
We’re here today to help answer some of these questions. What we’ll be doing is called “bird banding.” This involves examining birds in the hand, fitting them with uniquely numbered, lightweight leg bands, and then releasing them to continue with their lives. Mist nets are our tool, allowing us to safely capture the songbirds. And repeated over many years, this sort of research allows us to gain insight into these tricky questions of survival, productivity, and the health of bird populations.
Monitoring Avian Productivity and Survivorship
Today’s project is part of a massive, collaborative effort involving hundreds of bird biologists known as Monitoring Avian Productivity and Survivorship (MAPS). It’s a project focused on understanding how summer breeding birds are faring at specific stations throughout the United States and Canada. The focus is on those critical questions of the health of breeding bird populations: how many young fledge successfully? How many birds survive from one summer to the next? At each of roughly 350 MAPS stations—such as the one we’re at today—researchers band birds once every ten-day period throughout the summer. It’s a long-term commitment, five years at a minimum. And with each additional year, we get a more thorough understanding of local birds.
Today’s banding station at the edge of Grand Teton National Park got its start over 30 years ago, in 1991. Teton Science Schools founded the station just a few years after ornithologist Dave DeSante first launched the MAPS project.
“This is one of the longest-running MAPS stations in the country,” Hilary Turner tells me.
Bird banding and more
Hilary is the Program Coordinator for the Jackson Hole Wildlife Foundation (JHWF), a local nonprofit focused on wildlife conservation. JHWF started in 1993 with a group of concerned citizens who wanted to make Jackson Hole a more wildlife-friendly community. Since then, JHWF has removed more than 240 miles of fence from the landscape—enough to surround Grand Teton National Park—in order to make the landscape more friendly to the movements of wildlife. The organization also leads a variety of other wildlife projects.
Bird banding is one of JHWF’s more rigorous data collection projects. The organization operates two MAPS stations: this one plus another closer to the town of Jackson. In addition to Hilary, the core team of biologists at the stations includes lead bander Vicki Morgan and assistant bander Kevin Perozeni. These three run the banding stations, ensure safe handling of the birds, train volunteers like me, and educate community members about birds and bird banding.
Checking the nets
It’s time to check the nets again. Mist nets are not entirely flat; each one is designed with five “pockets,” folds of netting that stretch horizontally from one metal pole to the other. When a bird flies into the net, it tumbles into a pocket, where it rests until we arrive to free it.
Net Two is tucked into a narrow opening within a dense grove of aspens. As we approach, we can see a young calliope hummingbird resting in one of the pockets. Kevin deftly frees it and transfers it to his open palm, where he waits for it to fly off. We don’t band hummingbirds here. For such tiny birds, banding requires even more specialized training and isn’t covered under JHWF’s permits. The young hummingbird looks around, alert but perhaps slightly puzzled about what has happened. After a brief stay in Kevin’s palm, it flies off.
The rest of the nets in the aspen grove are empty this time. But Vicki, checking the nets closer to the stream and the beaver pond, returns with two birds for us to band: a young American robin and an adult cedar waxwing. She carries each one in a specially designed cotton bag, closed with a drawstring. The bags help the birds to stay safe and calm as we transport them. Back at the banding station, Vicki gives Hilary the bag with the robin. I watch over her shoulder.
Getting to know a robin
Hilary removes the young robin from the bag, handling it gently but firmly as she checks its condition. She uses the “bander’s grip,” holding the robin’s head between her index and middle finger, which prevents the bird from struggling or injuring itself. This young robin will be part of the season’s-end numbers of fledglings from this MAPS station—that index of productivity that is so important for understanding how our birds are doing. But that’s not all we can learn from this bird.
Hilary gives the robin a quick physical exam. This seems to be a healthy baby. Blowing on the bird’s breast feathers, she checks for fat stores on the body or under the wings. Right now there’s hardly any, which is expected at this time of year. During fall migration, on the other hand, songbirds can build up so much fat that banders call them “butterballs.” In migration, tracking fat levels becomes extremely important, telling us whether birds are managing to get the food they need to continue on their journeys in good condition.
Checking for molt
Now Hilary spreads the robin’s wing, checking the condition of the feathers. Feathers don’t last forever, and birds molt them in predictable patterns. Everything we’re seeing in this robin’s wing, Hilary tells me, are juvenile feathers. Compared to adult feathers, these ones are low-quality, grown as fast as possible to minimize the baby’s time in the flightless, extremely-vulnerable nestling stage. To make up for its not-so-great feather quality, in the next few months this baby robin will molt some, but not all, of its feathers. By fall, its spotted breast will be orange like an adult’s. Its back and head will be covered with new, sleek, gray body feathers. It will also molt some of its wing feathers, but not all of them.
Understanding the intricacies of how birds molt is a nuanced art of interpretation—and it’s one of the essential skills that all bird banders learn. Details of molt often differ between young birds and older birds, allowing banders to determine age. For example, in their first fall, juvenile robins molt some but not all of their fledgling wing coverts (the feathers that cover the longer primaries and secondaries). Adults, on the other hand, molt all of their wing feathers, including the primaries and secondaries, in one smooth, predictable process.
What molt tells us
Anyone can see molt in action as a spot-breasted baby robin grows its adult-like orange breast feathers—but bird banders, through a careful study of a bird’s wing and tail feathers, can generally identify teenage robins for almost another year. And for a program like MAPS, being able to distinguish first-summer, second-summer, and older birds is essential. With this information, biologists can look at the proportion of baby birds that manage to return in their second year, as well as how this compares with older adults.
Understanding molt patterns and what they can tell us about a bird’s age and condition is complex, and even skilled professionals are constantly learning. But for experienced biologists like Hilary and Vicki, giving each bird this sort of thorough physical exam goes quickly. Within a couple of minutes, the robin and the cedar waxwing have been aged, measured, weighed, and released. We’ve recorded all of it on our data sheets, and we’re ready for more birds.
MacGillivray’s warblers and cedar waxwings
One of our next birds is a MacGillivray’s warbler that flies into the net from the shady aspen undergrowth. Hilary tells me that these elegant warblers, with their fine charcoal heads and sunshine-yellow bellies, are among the most frequently-captured birds at this station. But outside of a bird banding project, MacGillivray’s warblers are secretive birds of shrubby thickets. I’ve never been this close to one before. Like the robin, this is one of this year’s babies, actively molting its head feathers from the quickly-grown juvenile ones to the more durable teenager plumage.
Throughout the forest around us, the Canada buffaloberries (Shepherdia canadensis) are ripe, their juicy red berries glistening in the shade. They’re rather bitter for many human palates, but the animals clearly like them. As I was helping Hilary set up nets just after sunrise, we found a large, fresh pile of bear scat nearby, filled with buffaloberries. Now, back at the banding table, it seems that the buffaloberries have returned to greet us. Hilary is removing a cedar waxwing from a bag that it has stained red with its fruit-filled poop. With so many buffaloberries fruiting, and few other berries around, we’re pretty sure we can guess what it was eating.
As Hilary gives this one its examination, she adds a few more checks specific to the waxwings. She measures the length of the yellow tip on the tail feathers; then she checks for waxy red tips within the wing, on the secondaries. In waxwings, younger birds have a thinner yellow band on the tip of the tail; it’s broadest on older males. Older birds also grow more waxy red tips on their secondaries. This bird has a moderately thick yellow band on the tail, but no waxy wingtips yet. It’s a second-year male, Hilary tells me.
Later in the morning, we catch a male western tanager in the aspens, his head a mildly flaming orange. Based on a careful examination of his wing feathers, Hilary confirms that this is a two-year-old. This winter, he’ll migrate south to Mexico, El Salvador, or Panama. He’ll expand his summer diet of insects and begin including a variety of fruits. And here in Wyoming, maybe we’ll meet him again next summer.
It’s through individual bird encounters like these, hundreds of them over the course of a season, that we begin to develop a larger picture of how the birds are doing in an area. Many of these birds disappear after the summer that they’re banded, and Hilary and her crew never see them again. Perhaps some of them move on to breed in a different area. Others undoubtedly succumb to the host of threats that birds face.
Each year, birds lose migratory stopover sites and overwintering habitats to housing sprawl, energy development, and agriculture. Insecticides and heavy metals poison birds from within the food chain. Tens of millions of outdoor cats kill well over a billion birds a year in the US alone. And the danger of window and vehicle collisions is every-present in birds’ daily lives. But in spite of it all, banded birds do return. And when they do, they give us a deeper glimpse into their lives.
Two days later, we’re at JHWF’s other MAPS station, a few miles west of Jackson near Boyles Hill. The morning sun is carrying wisps of mist off of the cottonwood-surrounded ponds, and the western wood-pewees are singing lazily. And today we’ve caught a warbling vireo that already has a band. In the hand, Vicki can tell that she’s an adult female, at least three years old.
The story of the vireo
Vicki blows on her belly, checking for evidence of breeding condition. “She’s not very far into her molt, so she still has her brood patch,” she notes. The brood patch is a bare region of skin on the belly where breeding birds, mostly females, will shed their insulating feathers. The bare skin is like an electric blanket, transferring the mother’s heat to her eggs or nestlings to keep them warm. Since this female vireo still has a brood patch, it’s a strong suggestion that she nested nearby this summer. And because she’s beginning her fall feather molt, we know she’s done nesting now.
Later, Hilary helps me look up this vireo’s band number in order to learn more about her. We find out that she was banded at Boyles Hill in June 2019, before the Covid-19 pandemic struck and turned human society upside down. She was two years old then—which makes her six now. And among all of the hazards of life as a migratory songbird, she’s managed to survive. Maybe we’ve banded some of her fledglings, too.
Invisible lives revealed
Bird banding is multifaceted, much more so than you might guess at first glance. It’s a chance to have a one-on-one encounter with a young MacGillivray’s warbler, molting its first-ever head feathers, and to wonder what life is like for all of the birds around us. For scientists like Hilary, Kevin, and Vicki, it’s a chance to develop a deep understanding of bird populations—and to collect essential information about their survival. For the entire network of MAPS collaborators, it’s an opportunity to contribute to conservation research that ranges from questions about how young birds may end up in low-quality habitat to examinations of the full annual cycle of Wilson’s warblers.
And for visitors to a MAPS station—including the 133 guests that JHWF has welcomed this year—it’s an invitation to be amazed by our feathered neighbors, to glimpse their lives and the challenges they face, and perhaps to fall in love with them.
To me, that’s a worthwhile way to spend a morning.
Albert, S., Ruegg, K., & Siegel, R. (2018). El uso de marcadores intrínsecos y extrínsecos para enlazar poblaciones de aves a través de las Américas. Zeledonia 22:1. Retrieved from https://www.birdpop.org/docs/pubs/Albert_et_al_2018_Use_of_Intrinsic_and_Extrinsic_Markers.pdf.
American Bird Conservancy. (2023). Cats indoors: cats and birds. Retrieved from https://abcbirds.org/program/cats-indoors/cats-and-birds/
Institute for Bird Populations. (n.d.) MAPS: Monitoring Avian Productivity and Survivorship. Retrieved from https://www.birdpop.org/pages/maps.php.
Pyle, P., Foster, K.R., Godwin, C.M., Kaschube, D.R. & Saracco, J.F. (2020). Yearling proportion correlates with habitat structure in a boreal forest landbird community. PeerJ 8:e8898. Retrieved from https://peerj.com/articles/8898/.