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The magnolia warbler travels as many as 2,000 miles, high above the Gulf of Mexico and across the entirety of the United States, before arriving in the cool climate of Canada’s boreal forest to breed. On a morning in May, one of the tiny yellow songbirds found itself entangled in a black net strung up in a clearing deep inside Pittsburgh’s Hays Woods. It had stopped here to rest and refuel, and the avian ecologist Nick Liadis fished the small bird from the mesh. 

Gently, he held the warbler’s neck between his index and middle fingers and measured the wings, tarsals and body fat. He weighed the bird, affixed a tiny aluminum alloy cuff to its left foot, and released it back into the forest.

The process, called banding, allows researchers like Liadis to study dozens of species of songbirds as they migrate each year. The data can be a valuable resource in understanding the complex local ecosystems in which the birds briefly reside. 

Songbirds reflect environmental changes; their presence and condition are a bellwether to an ecosystem’s delicate balance. 

“Banding data begins to put together a story about the health of the land,” said Liadis. 

The birds have completed the cycle of migration each spring for thousands of years; their routes evolved at a time when only trees, oceans and desert led the way. But human-induced urbanization and development, habitat loss, light pollution and climate change have altered the ancestral patterns of migration.

Warming temperatures have caused the insects that many birds rely on for food to emerge sometimes weeks before the migrants arrive. Invasive plant overgrowth and suburban sprawl have strained biodiversity and eroded the stability of local ecosystems.

Birds are an indicator species, said Liadis. “They can tell us about how different systems in a given environment are working and how healthy they are.”

This spring, millions of songbirds are flocking through the region, with much to say about its health. 

In Cities and Suburbs, Bird Lab Bands for Clues

Bird Lab, which Liadis founded in 2020, conducts research at three banding stations across distinct avian habitats in Pennsylvania—one each urban, suburban and rural—in an effort to study migratory birds, their conditions and the health of the ecosystems they inhabit.

In Chicora, Butler County, the rural Bird Lab outpost overlooks a former surface mine. For decades, the land was scarred by coal extraction and polluted by acid mine drainage. 

But today, after 35 years of reclamation and reforestation brought by an environmental art installation known as the Twin Stupas, the site has become a flourishing habitat for songbirds. 

“It all goes back to the abundance of native plants,” explained Liadis. Over time, the surrounding forest regenerated to support almost exclusively native species: Oak trees and native berry brambles, shrubby St. John’s wort and various types of wildflowers speckle the meadows. “There’s really good habitat,” said Liadis. 

“Migratory songbirds look out for native plants because they know that the relationship between insects and native plants has evolved over millions of years, and the birds have evolved alongside that,” he explained.

For some birds, the Twin Stupas is the last stop on a long and precarious journey. Liadis finds that songbirds are returning to the site year after year, and that many are staying to breed—a biological endorsement of the ecosystem’s health, and an indication that the once-downtrodden land has undergone transformational change.

Migration is one of the most energy-demanding parts of a bird’s life cycle, explained Liadis. Songbirds need to eat—a lot—and each leg of the journey requires them to fuel up a little bit more.

The birds know to pick certain trees for food, Liadis said. “So if the ecosystem does not have adequate native species, for example, that can reflect or impact the insect population, which in turn impacts the bird population.”

Liadis measures a bird’s fat stores, which can indicate whether there are ample sources of preferred foods like caterpillars and insects, which is in turn determined by the presence of native plant species.

If fat stores increase, that indicates that the bird is finding enough food in that habitat. If they decrease, it suggests that certain native plant species might be dwindling, and that reforestation efforts should perhaps prioritize their regeneration.

By comparing refueling rates, or how quickly birds are able to build their fat stores, Bird Lab can evaluate how well a given ecosystem is meeting the energy needs of migrant birds. 

The birds Liadis bands at the Twin Stupas generally have higher refueling rates than at the suburban site in Upper St. Clair, which suggests that the reclaimed mineland has regenerated ample native plant species and bird foods, and that balance has been restored to the ecosystem. 

Bird data can also reveal ecological problems and guide efforts to fix them.

In Hays Woods, invasive honeysuckle grows rampant, forming what bird researchers call a “migrant trap.” Large tracts of honeysuckle lure migrant songbirds because they appear thick and vegetated, but they don’t sustain the insect populations that birds need to refuel.

“It’s a wilderness up here. Nobody is managing the forest,” said Liadis.

Compared to the Twin Stupas, Bird Lab observes fewer birds breeding at Hays Woods and in the suburbs, and the recapture rate is lower, too. The research is still ongoing, but Liadis hypothesizes that depleted native plant populations, owing to invasive overgrowth or sprawl, are causing songbirds to favor locations with greater biodiversity, like the Stupas, as places to reproduce and return to year after year.

Bringing Biodiversity Back

“One of the biggest issues that comes along with invasive species is an overall lack of biodiversity,” said Robin Eng, ecological project manager at the Pittsburgh Parks Conservancy. 

Invasive plants form dense, aggressive thickets that push out native vegetation, she explained. “So rather than a Pittsburgh park that might have thousands of plant species, you end up with whole acres that really only have maybe ten species because they’re all invasive.”

Since 2020, crowdsourced bird data has guided an ongoing effort to restore biodiversity to Pittsburgh’s Frick Park’s urban forest ecosystem.

Using a citizen science app called eBird, hobbyists and amateur birders have documented the bird species that they spot in different parts of Frick Park’s Clayton Hill, and contributed to a growing dataset used by the conservancy and its research partners to measure the evolving health of the ecosystem and inform efforts to restore it.

The parks conservancy is four years into collecting bird data, and nearly a decade progressed in regenerating native forest habitat, which includes managing and removing invasives and planting diverse native species. 

Data gathered by citizen birders on Clayton Hill indicated that invasive Japanese stiltgrass threatened the ground-dwelling habitat of some birds. It showed that the Clayton Hill reforestation efforts should prioritize recovering the understory, or ground-level vegetation, said Eng, “so that ground-nesting birds and birds that forage for seeds in the leaf litter and on the ground have better habitat.”

Bird data also shows that some species of birds that need continuous forest aren’t being supported by the Clayton Hill ecosystem. “That is an indicator to us that maybe we need to focus on connectivity throughout the region, and focus on some of the more established, longer-lived forests that will support some of [those species].”

This spring, the conservancy planted 200 new trees across 25 native species on Clayton Hill: hemlocks, black gum and Virginia pines, bladdernut trees and pawpaws, among others. But it will be many years, and possibly decades, before their impact is reflected in the birds. 

“The longer we can collect this data, the better,” said Eng. “Trends over time are probably the most informative, not only to just the health of our ecosystem, but also to inform how effective or ineffective our management efforts are.”

Subverting Suburban Sprawl

In Ross Township, north of Pittsburgh, Lauren Nagoda is challenging what is typical in suburban America, where monolithic stretches of green lawns and manicured, non-native flora have become the dominant residential vegetation.

Nagoda ripped out most of her lawn and planted native bluestem goldenrod, spotted bee balm, fragrant sumacs and echinacea. She added water features, three birdhouses and six feeders.  She adhered bird-safe tape to her windows to make them avian-visible and prevent collisions — a leading cause of death for birds, along with outdoor cats. A sign in her front yard notifies passers-by (and perhaps birds, too) of the backyard’s status as a certified Audubon Society habitat.

The birds arrived within days: First came a palm warbler, and then a red-breasted nuthatch. Quickly, Nagoda’s backyard became a suburban songbird oasis, a rare island of biodiversity in a sea of sterilized sprawl.

“We have this vision that a house needs to have a nice green lawn in front of it. But you can begin to challenge that by planting layers of habitat,” said Liadis. “An oak tree is one of the single best things that someone can do in their yard.”

He described a trifecta: Plant an oak. Add birdsafe treatment to your windows. Keep your cat indoors. “Doing those three things can really, really help birds and their ecosystems.”

Carnegie Museum’s Vast Collection of ‘Flying Feather Dusters’

Even posthumously, songbirds can play an important role in the study of environments of the past.

Behind the walls of the Carnegie Museum of Natural History in North Oakland rest nearly 200,000 avian specimens. For researchers, the ninth-largest collection in the United States is a library of biodiversity and a valuable resource in studying how environments have changed over time.

Collections like the Carnegie’s are sometimes the only way we can go back to study the ecosystems of the past, explained Serina Brady, collection manager for the Section of Birds at the museum.

In 2017, using specimens from the Carnegie collection, researchers studied the amount of soot that had collected on the wings of more than 1,300 individual birds. Using bird data, scientists were able track atmospheric soot concentrations between 1880 and 2015 within the Rust Belt.

Researchers found that soot concentrations in bird’s feathers corresponded with periods of coal consumption and poor air quality: Birds were cleaner during the Great Depression when less coal was burned, and they became dirtier during the industrial boom of World War II. By mid-century, city-level regulation had all but eliminated residential coal heating, and birds were clean once again.

“They were literally flying feather dusters, sampling the air quality at that time,” said Brady. “Using museum specimens, we can reach back in time to see what the environmental quality was like.”

Some species, however, continue to elude scientists. 

Once commonplace in Southwestern Pennsylvania, the evening grosbeak has experienced a decline of nearly 90%. These days the black and yellow bird is seldom found as far south as Allegheny County’s 40 degrees of latitude. 

The evening grosbeak’s virtual disappearance from the region has prompted scientific inquiry into its mysterious decline. 

Researchers like David Yeany, of the Western Pennsylvania Conservancy, posit that changes to spruce budworm populations, loss of old growth forests, window collisions, disease and climate change could all have a hand in the grosbeak’s departure.

The evening grosbeak once played a role in maintaining the balance of local ecosystems, and its disappearance could lend clues to the ways in which environments change over time—and the measures that could preserve habitat for the species that remain.