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Net results: 40 years of bird-banding brings a wealth of data to Powdermill program

Monday, May 21, 2001

By Don Hopey, Post-Gazette Staff Writer

The white-eyed vireo flitted around the ponds and through the cattail marshes, hedgerows and brushy alders of the Powdermill Nature Reserve on a sun-splashed early May morning. Then, like a knuckleball into a catcher's mitt, it plopped softly into a billowed mist net.

Field ornithologist Bob Mulvihill removes a frightened tufted titmouse from a mist net at Powdermill Nature Reserve on a Friday morning in early May. (V.W.H. Campbell Jr./Post-Gazette photos)

The bird struggled briefly, its feet tangled in the fine-threaded netting, before Robert Mulvihill arrived to deftly pull it free. He dropped the bird unharmed into a brown paper bag and closed the bag with a clothespin.

After checking the rest of his nets, Mulvihill returned to a sparsely furnished lab in a whitewashed, cinderblock building. There, he identified and banded the bird, carefully recording information about its age, sex, wing length, fat deposits and body weight.

Placing the tiny aluminum tag imprinted with a code number and U.S. Fish and Wildlife phone number on the bird's ankle and recording the information took less than a minute. Mulvihill then released the bird through a small sliding wooden door in the banding lab window.

The whole process hasn't changed much in 40 years, and its low-tech sameness, 300 days a year, year in and year out, is one of its strengths.

On April 24, the longevity of the banding program, started as a Carnegie Museum of Natural History pilot project in 1961 by Robert Leberman, was rewarded when it captured and banded its 400,000th bird.

Within the next week or so it will pass another milestone as the number of original bandings and recaptures of previously banded birds hits 500,000.

"This is one of the oldest bird banding programs in all of North America, and the oldest professionally staffed, year-round program going," said Mulvihill, a 43-year-old field ornithologist. He has worked at the 2,200-acre research center abutting Forbes State Forest in Westmoreland County since 1978, when he arrived as a volunteer.

"The data we have collected on these birds over a long time shows consistent patterns. It's a phenomenal research tool."

Special, and not so special

Over its four decades of operation, Powdermill's avian research program has banded about 10,000 birds a year and collected data on nearly 200 species, ranging from hummingbirds to pileated woodpeckers to the occasional raptor and 40 different kinds of warblers.

This year, the program's spring bird count -- a running total that's available on the Powdermill Web site -- is up to 997 birds and 76 species.

Materials used in banding.

Because virtually all of the data has been collected by Leberman, Mulvihill and a stable group of volunteers, the database is among the cleanest, most internally consistent, of its kind. It provides information about bird populations and diversity, including longevity in wild bird populations, differences in migration behavior between species and between sexes and age groups within species, bird life cycles, weight and plumage changes.

"We're studying birds in all seasons. We could have 100 records of some resident birds, or just one of various transients or migrants. Others we know return here to breed, while other species are winter residents that migrate north in the spring," said Leberman, 64. The field ornithologist was one of the first to use mist netting, originally imported from Japan, to do bird banding and study.

"We field lots of data requests and, as people become aware that the data set is based on half a million bandings over 40 years, we expect those to increase."

M. Graham Netting, director of the Carnegie Museum of Natural History in the 1950s, was the one of the first to recognize the value of studying songbird migration away from established migration routes along the East Coast.

"There's nothing special about Powdermill and that's what you want," Leberman said. "There's no special concentration or migration route. This is just another valley in the Appalachians and, as such, gives a truer picture of what's out there."

Studying migration in detail

The greatest number of species fly through the area this month, but the greatest number of birds counted and banded occurs in the fall, when avian populations are swollen with birds hatched in the spring and not yet reduced by over-wintering mortality.

The tufted titmouse Mulvihill retrieved from a mist net takes its unhappiness out on his finger.

"Today we'll have vireos, warblers, sparrows and thrushes, among others," said Leberman, who has authored or co-authored 20 research papers based on the banding data. "We have a lot of diversity because of our elevation here and because we are at the ends of northern and southern migration routes."

One of Leberman's research areas involves differential migration -- by species, sex and age groups.

And six years ago, Mulvihill began a study of the Louisiana water thrush, with preliminary results showing that breeding density for the species declines significantly when its stream habitat is degraded by acid mine drainage.

Data collected at Powdermill may also help researchers determine if global migration is related to and affected by trends in global warming.

Despite sometimes large annual variations in migrant populations long-term trends do not show significant differences, Mulvihill said.

"The timing of migration is related to mean spring temperature but so far we haven't been able to show a trend on temperature," he said. "Still, we have reason to believe that there would be an effect on migration if there is global climate change."

Also adversely affecting migration and bird populations is urban sprawl and development, which cause loss of valuable bird habitat, though there is little evidence of that at rural, wooded Powdermill.

Mulvihill said that fragmented landscapes are bird population "sinks" that lead to declining bird populations, while rural and wooded areas -- including the vast northern tier and middle sections of Pennsylvania -- are "population sources."

"We're grateful for the environment around us," Mulvihill said, "but there are increasing pressures from development and road building even here. And I can say without qualification that fragmented habitats are negative for biodiversity. By monitoring for as long as we have we will have benchmarks to check."

Yellow-rumped thrill

At morning's first light, Mulvihill unfurled the mist nets, and five hours later he is still walking quickly with long strides along the narrow boardwalks that parallel the nets and keep him from sinking into the marshy land.

 
    For more information

To learn more about Powdermill and the bird banding program, visit www.clpgh.org/cmnh/powdermill

 
 

"Watch out for that fox scat," Mulvihill said over his shoulder as he jumped over the small pile at the end of a well-weathered board. "We see bobcat, fox and coyote visit here. We have to be alert to that type of thing, but we really have no significant problem with predation."

That those animals would know where to come for an easy meal isn't surprising. The 50 mist nets, each 7 feet high and 40 feet long and placed in hedgerow gaps and along habitat edges, must look like a cafeteria line to the predators.

And that the foxes, bobcats and coyotes go away hungry more often than not is a tribute to the speed, dedication and more than 60 years of experience that Leberman and Mulvihill bring to their work.

What their work still brings to them is excitement.

Mulvihill, who could identify most birds when he was 10 and came to Powdermill for the first time, remembers it as a life changing.

"I came out here on a visit and realized I could do this," he said. "I was fascinated by the nuts and bolts of banding and that brought my scientific curiosity into play."

That fascination and curiosity is reflected in his answer to a question about his most memorable banding day at Powdermill.

"It was actually two days. One was when we worked to band the largest number of birds -- 576 in 1982 -- that I ever banded in a day," he said. "The other was the day we banded the largest diversity of species -- 53. It was a phenomenal experience to handle that many kinds of birds in one day."

Leberman, who once captured and banded 650 birds in a single day before Mulvihill worked at Powdermill, said his most memorable day was Sept. 21, 1971, when he found a Kirtland's warbler in one of the nets. It is the only endangered species ever captured at Powdermill.

"It was a busy day and there were also 11 yellow-rumped warblers in the net," Leberman said. "I knew what it was immediately, but I finished doing the common birds before I let myself deal with the reality of finding that really rare species."

The Kirtland's warbler breeds in Michigan and winters in the Bahamas. When Leberman found one in his net there were only 200 known pairs in the world.

"It wasn't biologically important but that day stands out for me," he said. "You could never have predicted that out of 400 birds in the world, one would show up in Pennsylvania.

"That's what keeps me going every day. There's always something new in the nets."



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