A turkey vulture, one of several Pennsylvania vultures trapped and tagged with a satellite telemetry unit in 2004, was resighted a month ago in late June. Raptor researchers spotted the vulture in a forest in New Jersey, just across the Delaware River from Riegelsville. This is less than 50 miles from the location where it was originally captured — more than a decade ago — at a dump in Pen Argyl, in Northampton County.
According to Keith Bildstein, the director of Conservation Science at Hawk Mountain Sanctuary, the sighting was unusual for two reasons — the age of the vulture and the length of time that the transmitter has been functioning, still providing valuable information.
Upon its original capture nearly 11 years ago, the adult vulture — named Irma Broun in honor of the Sanctuary’s first volunteer — was fitted with two data-collecting devices. A solar-powered backpack-style satellite tracking device is worn externally and an internal data logger had been surgically installed.
“The tracking units we used are estimated to work anywhere from three to five years, so this one is a real overachiever,” joked Bildstein.
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A decade’s worth of data showed that the female vulture migrated to South Jersey during the winters of 2004-2005 and 2005-2006. Since then, she has been a year-round resident of an area near Easton and Phillipsburg, N.J., shuttling between feeding and roosting sites on both sides of the Delaware River.
“This data is a wonderful thing. It tells us where they have gone and where they die,” commented Bildstein. “Combined with a necropsy, it also tells us what killed the vulture. This is wonderful information for raptor conservation. Although we know that the first year of life is tough on most raptors, including vultures, specific information regarding how they meet their demise is an all-too-rare commodity among conservationists.”
Success with the internal data logger has been a different story.
“Working with a veterinarian, back in 2004, we placed a data logger in the bird’s body cavity to record core body temperature and heart rate. It meant that we would need to recapture the bird the following year to extract the logger and download the data to learn how turkey vultures use and save energy during migration,” Bildstein explained.
Five other turkey vultures were also fitted with internal data loggers — four were recaptured, but not Irma. According to Bildstein, three of the four monitors failed, and the fourth provided only 38 days’ worth of heart and body temperature data.
“Those devices cost $2,000 each, and we really got burned when they didn’t work,” Bildstein said. “However, those 38 days of data have proven very valuable. We learned that vultures exhibit controlled torpor — able to lower their core body temperature seven to eight degrees Fahrenheit each night. This lowers their metabolic rate and is big energy savings for the birds.”
Turkey vultures are certainly not a “glamour species,” such as cardinals or bald eagles, but they perform an important ecological function. According to Cornell University Lab of Ornithology, vultures are opportunistic feeders — cleaning up road kills and hunter gut piles. They are widespread in both North and South America. Commonly called “turkey buzzards,” these vultures were rare in Pennsylvania a century ago; however, they have now pushed northward into Canada. Black vultures, a southern species, are following the same pattern and are just now making their presence known in Pennsylvania.
The Hawk Mountain study is on-going — another eight vultures (four turkey and four black) were captured and fitted with transmitters and/or wing tags on July 16. The capture site was on a farm east of Hawk Mountain in Kempton, Berks County. According to Sanctuary spokesperson Mary Linkevich, this particular phase of their vulture research has been funded by the Pennsylvania Wild Resource Conservation Program. Other parts of the vulture research are being funded by private donations, as well as the Pennsylvania Game Commission.
“In this case, the Wild Resources Program paid for two GPS units that were placed on black vultures,” Linkevich said.
Costing well over a quarter million dollars, Hawk Mountain Sanctuary’s vulture research is much larger than a few Pennsylvania turkey vultures. According to Bildstein, 14 turkey vultures were fitted with transmitters in Pennsylvania and 57 total in the United States, Canada and Argentina.
History was made in 2011, when Hawk Mountain researchers were simultaneously tracking South American turkey vultures as they migrated north toward the equator and North American turkey vultures as they moved south. No other species of raptors has ever been tracked from breeding areas both north and south of the Equator at the same time.
“What we learned is that turkey vultures in the southern hemisphere behave in a mirror image of those in the northern hemisphere,” commented Bildstein in a recent telephone interview. “The vultures that live closest to the equator migrate the least, and those that breed farther away migrate the greatest distances — sometimes thousands of miles.”
Hawk Mountain’s long-term strategic plans call for continued investigations in hopes of better understanding the biology of this species, which they plan to use as an ecological sentinel for environmental contaminants.
Researchers from Hawk Mountain Sanctuary hope to recapture Irma and replace her aging satellite tracking device with a new one. As for the internal data logger, those secrets, if there are any, will remain untapped.
“This vulture is too valuable for us to put her through the risk of surgically removing the internal data logger,” Bildstein noted. “This is especially true when you consider that three out of the four units already recovered have failed to record anything.
“We live in a golden era of raptor migration science, which also puts us in the golden era of raptor conservation,” Bildstein added. “We are doing things that I only dreamed about as a graduate student in the late 1970s.”