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An hour's drive east-southeast of Pittsburgh, hidden among the picturebook-perfect red barns, white fences, and green fields of the Lignonier Valley, lies an equally carefully maintained landscape of bird research—a nature preserve whose ponds and wildflowers have been augmented with mist nets, field microphones, a songbird recording booth, and a one-of-a-kind rotating flight tunnel.



On a recent morning, Venue joined researchers Luke DeGroote, Amy Tegeler, Mary Shidel, Kate Johnston, and Matt Webb, as well as several dozen warblers, catbirds, and a cuckoo, for a tour of the various devices of bird surveillance at the Powdermill Avian Research Center (PARC), part of Carnegie Museum of Natural History's Powdermill Nature Reserve.

Founded in 1961, PARC is the longest-continuously running bird banding station in the United States, and has assembled one of North America's largest census data sets on migratory songbird populations. Six days a week during the spring and fall (and only slightly less often during the winter and summer), DeGroote and his team head out before dawn to unfurl the Center's 61, forty-foot long, eight-foot tall nylon mesh mist-nets.

Over the course of the morning, until either the temperature reaches 78 degrees or the time hits 11 a.m., whichever comes first, these superfine, over-sized volleyball nets form a network of barely visible barriers stretched between trees, along the banks of artificial ponds, and hanging parallel to overgrown hedgerows, trapping both droplets of dew and unwitting birds from the atmosphere.



The majority of the nets have stood in the same place for the past half-century, raised and lowered each day to create a sort of avian calendar, marked by the arrival and departure of different species within the northern Appalachian landscape. Indeed, as we accompanied DeGroote on his rounds, he noted that the preponderance of warblers signaled that the spring migration was drawing to a close.

While carefully untangling a Kentucky Warbler and a stunning Scarlet Tanager (the first male of the season, apparently) from the first net, and stowing them in cloth bags attached to a system of color-coded carabiners he wore on a chain around his neck, DeGroote explained that the landscape is pruned and maintained to remain as similar as possible to its 1970s "early successional" state: arrested in a state of post-agricultural regrowth that will never be allowed to mature into secondary forest. The more things the banders can keep the same within their own research ecology, the more valuable their data becomes for detecting changes in bird populations and behavior. It is both a control landscape, anchoring the variables of the various experiments, and a landscape of control.



Bird-banding, we quickly realized, does not make for a relaxing morning. Every minute spent away from its normal activities eats into a bird's valuable refueling and breeding opportunities, so PARC's operation is set up with assembly-line efficiency. Back at the banding station, DeGroote and his colleagues unhooked bird bags from their necks and hooked them onto a washing-line pulley for processing.

PARC catches roughly 13,000 birds each year (their up-to-date tallies are posted online), 3,000 of which are recaptures. The other 7,000 need to be issued with a unique 9-digit number ("bird Social Security," joked DeGroote), which they will carry with them for the rest of their lives on a small aluminum cuff gently fitted around one leg. On the wall, behind the bird pulley, was a map showing all the places PARC bands have been reported, with sightings as far afield as Peru.

DeGroote held a bird in one hand and typed with the other, measuring and entering data on weight and wing length, all the while continuing a running commentary on sage grouce dance-offs, the particular chirrup a bird makes when it is released ("like it's saying 'potato chip'"), and the dietary choices to blame for the cuckoo's notorious stink (too many caterpillars). By blowing gently on the birds' stomachs, he revealed more data points: their fat stores (visible through translucent skin) and breeding condition.



The only pause in the otherwise seamless process came when trying to determine the birds' age. The quality of their feathers is apparently the main giveaway—baby birds grow all of their feathers in a hurry so that they can get out of the nest, and then have to regrow some to a higher standard. The difference is almost impossible for a novice to spot—the juvenile feathers have slightly less of sheen, and the plumage pattern is muddier—and it is sometimes quite challenging even for experts.

As we watched, hypnotized by the banding team's practiced, economical motions, PARC's bird processing line ground to a brief halt over the cuckoo, whose spotted tail feathers were of inconclusive quality. DeGroote pulled down a reference book to look for additional clues before playing it safe with a broad "older than two years" designation, and swinging smoothly back into action.

Even the architecture had been modified to account for this avian activity: a small hole in the wall, complete with a sliding panel, acted as a quick-release hatch for any birds not destined for additional research. With the banding as its baseline activity, PARC balances releasing birds quickly with the opportunity to conduct additional research, and this season was also hosting a West Nile virus swabbing station, as well as its own ongoing programs for flight tunnel and bioacoustic research.



We accompanied Amy Tegeler, the bioacoustics program manager, over to her recording studio, with a gorgeous and talkative black, orange, and yellow American Redstart in tow.

In addition to its mist nets, the landscape around PARC is also miked, with three pole-mounted "sky ear" recording devices, based on a simple plastic flowerpot design originally developed by Bill Evans.



As they migrate, most songbirds emit short, single-note nocturnal flight calls. No one, Tegeler explained, is quite sure why they do this—she likened it to trying to make a phone call while running a marathon—although the generally accepted hypothesis is that it has to do with maintaining flock spacing and cohesion.

Researchers are not only interested in learning about these nocturnal calls for their own sake, however: the idea behind PARC's bioacoustics program is that, by using software to analyze recordings of the nocturnal soundscape, it will be possible to conduct a remote, automated census of migration and species numbers.

This, Tegeler was quick to explain, won't replace bird banding. Instead, a bioacoustic survey can pick up species that aren't often caught in nets, can be used in environments that would be difficult for humans to reach or set up nets in the first place (remote rainforest and cities, for example), and offers the opportunity to conduct lower-resolution counts across a larger landscape (perhaps even as a citizen science effort—the microphone costs about $50 to make out of parts readily available at a hardware store and RadioShack).



While exciting, the technique is still in its infancy, and the Raven Pro software that Tegeler uses to extract flight calls from the hours of night recordings—cross-species cryptanalysis as app—also flags, unfortunately, each and every raindrop impact as a bird. After spring migration season, Tegeler estimates that she ends up with 75,000 audio clips, only 5,000-10,000 of which are actually calls. Sorting through the terabytes of data takes months.


Andrew Farnsworth and colleagues developed this 2006 guide to warblers' nocturnal flight calls using field recordings. A larger version, with sound samples, can be seen/heard at the Cornell Lab of Ornithology's website.

To help improve the call identification process, PARC has built a custom-designed bird recording studio, which it uses to capture a "Rosetta Stone" library of "clean" nocturnal flight calls, to replace the fuzzier field recordings currently used as reference.

To demonstrate, Tegeler dropped our Redstart into an "acoustic cone" (actually a black-out fabric cylinder built from a long-sleeved T-shirt and two embroidery hoops from Jo-Ann), hung it between four mics in a soundproof booth, closed the door, and sat down at the control desk with her headphones on. The whole set-up looked like something Paul McCartney might use to re-record a vocal track—that is, if he liked to sing suspended in mid-air in complete darkness.



With her headphones on, Tegeler played our avian rock star two minutes of American Redstart nocturnal flight calls recorded in the field, interspersed with silence, and the croak of a spring peeper frog as a control. From within the booth, the bird responded to the calls with four high-pitched squeaks—in the process, yielding a perfectly clean recording for Tegeler and other researchers in her field to work with.


Spectrographs of the nocturnal flight calls of the American Redstart (left) and Savannah Sparrow (right), from Bill Evans' spectrograph library.

With most common birds recorded, this migration season, Tegeler has been collecting data to try to establish what other information, beyond species identification, is embedded in nocturnal flight calls.


Zeep, double-banded upsweep, and single-banded downsweep nocturnal flight calls, from Bill Evans' spectrograph library.

"There are patterns to the calls, but we don't yet understand why, or what they mean," Tegeler explains, adding that the calls themselves can be separated into distinct types, named for their sound: buzzy, zeep, upsweep, downsweep, and chip. An entire acoustic ecosystem awaits decoding: some species will respond to other species' flight calls, others, for reasons known only to themselves, won't; and Tegeler can detect variations within a species' calls, based on an individual bird's age and sex.


Diagram showing the moon-watching technique developed by George H. Lowery Jr from Gatherings of Angels: Migrating Birds and Their Ecology, edited by Kenneth P. Able. The original caption explains that "as birds cross the disk of the moon their flight paths are coded as 'in' and 'out' times on an imaginary clockface. All paths are then analyzed to produce a migration traffic rate—the number of birds crossing 1.6km per hour."

Astonishingly, before bioacoustic research got started just a few decades ago, the only way to gather data on nocturnal bird migrations was a technique called "moon-watching," in which researchers and volunteers would point a telescope at a full moon from twilight until dawn, counting and identifying birds silhouetted against its disk.

Now, nocturnal flight call surveys are matched with radar bioscatter analysis in a new scientific discipline called "aeroecology," or the study of the planetary boundary layer and lower free atmosphere as a biological ecosystem.


A screengrab showing "Composite Reflectivity in the National Radar Mosaic" from the SOAR (Surveillance of the Aerosphere Using Weather Radar) website.

Meanwhile, bioacoustic bird monitoring is just one area of an emerging field of acoustic ecology: researchers are using sound to assess population shifts in species as diverse as whales and bark beetles, while the National Park Service recently recognized soundscapes as an intangible asset, worthy of historical protection, and has begun installing field microphones across their lands to conduct a system-wide acoustic survey.


An acoustically instrumented landscape at Kenai Fjords National Park; photograph courtesy the National Park Service.

From the ways in which humans use invisible information to see birds, we moved to the bird's final stop in their short, PARC-assisted detour—a device designed to test how birds see human infrastructure.



One of only two bird flight test tunnels in the world, this prototype was built in partnership with Christine Sheppard of the American Bird Conservancy, in order to test how birds interact with different window treatments. An astonishing number of birds—more than a billion, according to the most recent estimates—die each year as a result of flying into the glass facades of urban America.


Clouds reflected in the Time-Warner Center towers in New York City (left) and a temptingly plant-filled glass atrium (bottom left) are among Christine Sheppard's collection of bird-unfriendly buildings. In her caption to the top right image, Sheppard notes that "architectural cues show people that only one panel on the face of this shelter is open; to birds, all the panels appear to be open." All photographs by Christine Sheppard, American Bird Conservancy.


Birds killed by building collisions, collected by monitors with FLAP (Fatal Light Awareness Program) in Toronto, photograph by Kenneth Herdy, via the American Bird Conservancy.

Sheppard's goal is to measure "relative threat values" for different kinds of glass patterns or finishes, in order to develop a recommendation for the most bird-visible (and thus bird-friendly) glass. And the device she has designed to do that is extraordinary: a stretched-out shed combined with the trompe-l'oeil trickery of a Baroque cathedral.

Matt Webb, the technician in charge of these bird/window strike-avoidance studies, retrieved a bagged Grey Catbird from the banding station ("they love flying in the tunnel"), in order to show us how the system works. He released the Catbird from its bag into a tiny hole at one end of the tunnel, and, as it flew down the ten meter-long darkened shed, a video camera recorded the bird flying toward the plain glass control panel covering half of the tunnel's other end, rather than the crazy-paving patterned glass on its right.



As we braced sympathetically, anticipating impact, the bird was saved by an invisible mist net (the same kind the banding team use). It hopped about in the felt-lined tunnel, completely unharmed and making the miaow-ing sound for which the species is named, while Webb logged the result, walked around to the side, opened a small door in the tunnel wall, and released it.

This particular manufacturer's "bird-friendly" glass, Webb told us, has a 73 percent avoidance rate, meaning that out of 120 tunnel test flights (each using a different bird), 88 had presumably seen the pattern, and chosen to avoid it by flying toward the clear—and hence invisible—glass to the left.



Not all birds are suitable research subjects, Webb explained: Yellow Warblers "get confused" and fly around in all directions; our vocal friend the American Redstart often sees the safety net, rending the whole test moot; and House Sparrows and other cavity-nesting birds simply make themselves at home in one of the tunnel's dark corners.

The tunnel itself is an experimental prototype: it is based on a design originally created by Austrian scientist Martin Rössler to test free-standing glass panels used in highway barriers, and Sheppard is already fine-tuning the next-generation tunnel from her base in the Bronx.

Briefly, it is worth noting some resonances here between Sheppard's architectural design for tracking and framing bird flight and a body of much earlier work done by bio-media pioneers such as Étienne Jules-Marey, who performed his own controlled studies of bird flight.



Jules-Marey's work combined innovations in multi-lens camera design and wearable media for birds with an interest in the science of flight to produce astonishing documents of animal bodies in motion.



These often took surreal form, including a proposal for hooking birds up to a machine that could register individual wing beats.



In any case, at the moment, Sheppard's current flight-monitoring structure is mounted on a turntable so that it can follow the sun, thus ensuring that its mirrors bounce sunlight onto the front of the glass at the same angle all morning. Inside the tunnel, and for the birds that fly through it, it is always the same time of day.

When we followed up with her by phone, Sheppard explained that this feature, while ingenious, is not perfect:

On a cloudy day, for example, you're going to have a break in the clouds that's nowhere near the location of the sun, but it's still the brightest part in the sky, and that will throw the reflections off.

One of the things that we're most interested in studying is ultraviolet patterns, because birds can see UV and we can't, but the mirrors we're using to reflect light onto the glass surface take out more of the UV in light than they do other wavelengths. At the moment, our flight tunnel handicaps the UV patterns.


In Sheppard's new design, the entire tunnel is housed in a shipping container, which allows for a much more closely controlled, and potentially more sophisticated, set of lighting parameters, in which an array of "daylight" and UV bulbs can be set up to mimic a variety of natural solar conditions.

The shipping container also weather-proofs the structure: although we visited on a sunny, calm morning, the current tunnel has been known to pivot with a sudden gust, giving bystanders a nasty shock.

Most important, however, is the fact that the new tunnel will increase capacity. "With only one tunnel," explains Sheppard, "we actually can't do enough testing to conduct our own research and test prototypes for glass companies that are trying to develop products for bird-friendly design. And, because we definitely want to encourage the market for bird-friendly products, we've been doing a lot of commercial testing over the last two years."



Even as scientists move toward a better understanding of avian perception (Sheppard told us of one project to build a model of the avian retina using a digital camera equipped with a series of specially designed filters), they still can't necessarily model how the bird will react to that visual information—"the 'what do the birds think about this?' question," as Sheppard puts it.

Will a bird think it can go through a space in between stripes? What about if the lines are diagonal? Will birds perceive a cobweb pattern as an obstacle?

Although the American Bird Association already knows (and recommends) several strategies for bird-friendly design, their goal is not to arrive at a single avian-endorsed glass solution. Instead, Sheppard says:

What we want is to create the situation where architects have maximum flexibility, and they don't feel like bird-friendly design is a burden. We're not trying to get them to stop using glass, and we're not trying to make them to design ugly buildings; we want to give them lots of different possibilities. To do that, we have to ask these birds a lot of different questions.

In other words, PARC's spinning, elongated garden shed, with its trompe l'oeil sky, wing mirrors, and slide-in glass panels, is a cross-species translation tool—a structural device designed to test whether the built environment makes perceptual sense both to people and to birds.



As the last stop on our tour of this well-oiled bird surveillance machine disguised as a nature reserve, the flight tunnel provided an intriguing counter-perspective, asking, in this artificially shaped landscape disguised as a natural preserve, how birds see our habitat and what their perceptual frame might require from our own future designs.

Grafton Tyler Brown & Co. map of the Comstock Lode and the Washoe Mining Claims in Storey & Lyon Counties, Nevada, published in 1873, via.

Although tourism is now Nevada's largest employer, the state was born from a mining boom in the 1860s, inspired by the discovery of a rich vein of silver ore christened the Comstock Lode.

Extraction still plays a signficant role in shaping the state's landscape and economy: the Nevada Bureau of Mines and Geology lists 29 gold and silver mines in its 2010 Mineral Industry Census, alongside claims that the state "continues to be in the midst of the biggest gold boom in U.S. history," producing up to eight times as much over the past thirty years as California did during its fabled Gold Rush.


Mine tour photographs by Nicola Twilley.

To get a glimpse of the state's subterranean origins, Venue visited Chollar Mine in Virginia City, which, between 1859 and 1942, yielded enough silver (and some gold) to rank as the third most productive mine on the Comstock. Curiously enough, it's now offered for sale, along with some mineral rights, although our guide assured us that it's much more viable as a tour business than as a working mine, given the flooding in the lower levels, the effort required to retrieve the remaining ore, and the not-insignificant cost of all the impact studies and permits needed to start a mining operation in Nevada today.


Gorgeous U.S. Geological Survey maps of the shafts and tunnels of the Comstock mines, published in 1881. The different colors used indicate each separate hundred feet of depth. From the David Rumsey collection in the Harvard University digital map library.

The Comstock Lode is legendary not just for the mineral wealth it yielded (an inflation-adjusted $400 million in silver per year, plus another $270 million in gold, at peak production in 1877), but for its role as a catalyst for extraction technology innovation.

As our guide explained, one of the major challenges faced by the miners was an ongoing battle against flooding from below by geothermal waters. When the Chollar Mine teamed up with neighboring mines to sink a new shaft to 3250 ft., they had to pump out 5 million gallons of water per day, as well as construct a special underground cooling chamber by lowering in big blocks of ice and buckets of ice water. Workers would spend 15 or 20 minutes working in the heat, and 15 or 20 minutes recovering in the cooling chamber, back and forth throughout their eight-hour shift.


The odd-looking structure to the right-hand side of the photograph is the head of the Combination Shaft, the deepest ever sunk on the Comstock, and so-called because it was a joint effort between the Chollar, Potosi, Hale & Corcross, and Savage mines.

In response, a 30-year-old German immigrant called Adolph Sutro proposed a wildly ambitious solution — drilling a 4-mile tunnel into the mountain that would use gravity to drain its mines from below, while simultaneously allowing equipment and ore to be shipped in and out at valley level rather than lowered and hauled up and down the mine shafts.

Work began on the Sutro Tunnel in 1869 and it opened in 1878 — but, by then, the Comstock had passed peak production, and improved ventilation and pump technology had already delivered many of the tunnel's proposed benefits. Sutro unloaded his own shares as soon as the tunnel was completed, and while his stockholders lost millions, he moved to San Francisco and became mayor.


The Sutro Tunnel entrance, then and in 2007, via the Library of Congress Historic American Buildings Survey and Rich Moreno.

The Sutro Tunnel has caved in in places now, and its entrance is off-limits, on private land. It is, nonetheless, a remarkable engineering landmark, and the direct forerunner of the large access and drainage tunnels still used by mines today.


Our guide told us this story while we stood 100 ft. underground in a stope — an auditorium-like hollow that had been mined out. Shored up tunnels and shafts led to more stopes, all around and beneath us — some as big as skyscrapers. And, in the second of the Comstock's engineering marvels, all of these underground voids are filled with cubes of heavy girders, arranged in regular grids like a wooden honeycomb inside the earth.


A cross section of Virginia City's Belcher Mine, via the Nevada Historical Society.

According to a 1912 history of Nevada, this "square-set" timbering system was invented by another German, Philipp Desdeheimer, as a modular solution that could be extended in any direction, "so as to fill in any ore-chamber as fast as the ore is taken out."

The unit in itself lies within the scope of a man's arms, but, built up in a series, it filled the vacant spaces left by the removal of the Con Virginia bonanza, hundreds of feet in height, in width, and in length.

The resulting lattice-work of notched timbers, held in place by the pressure of the rock all around them, looks uncannily like the skeleton of a skyscraper, stripped in order to construct its mirror image above ground.


A lumber mill at Lake Tahoe, via.

Indeed, as the miners followed the vein of silver further into Mt. Davidson, more than 100 square miles of old growth pines around Lake Tahoe were clear-cut, with the forest brought underground to replace the minerals. Logging, our guide told us, quickly became the second biggest industry in Nevada, as the territory's newcomers rushed to rearrange its resources.

This gridded timber superstructure, stretching for miles underground, as the rocks whose place it took were transmuted into coin, forms a sort of forgotten Continuous Monument of extraction — a ghost forest built underground, in search of silver.

Thanks to Ronald James, the Nevada State Historic Preservation Officer, for the suggestion. If you think of any sites or people that Venue should visit, please let us know!
 
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