An hour's drive east by southeast from 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, 40-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 avoiding collisions.
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.
To help improve the software identification rate, 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.