UNIVERSITY PARK, Pa. -- An ongoing cooperative study of fawn mortality between Penn State's College of Agricultural Sciences and the Pennsylvania Game Commission at two sites in central Pennsylvania has revealed that black bears are a major predator of young white-tailed deer.
Wildlife biologists knew that black bears kill an occasional fawn, according to Justin Vreeland, graduate research assistant in the Pennsylvania Cooperative Fish & Wildlife Research Unit, but they were surprised about how many.
"We didn't really expect to find that Pennsylvania black bears are the efficient predators of fawns that they are," he says. "It is widely known that the state's large population of coyotes prey on fawns, but it now looks like bears kill as many, possibly more."
Because deer numbers are stable and have been growing in Pennsylvania, Vreeland is quick to point out that predation is not impacting the herd significantly. He notes that there is a good reason why most fawns are born during a two-week period in late May and early June.
"Most fawns drop in the same time period and their numbers overwhelm predators," he says. "The odds are good for an individual fawn surviving. Does in Pennsylvania deliver from one to three fawns a year, depending on factors such as food, habitat and weather."
However results from his 16 months of Game commission-funded research -- where 218 fawns were captured, fitted with radio collars, then released and monitored -- show that many don't make it. Mortality from predation in the wild ranges from less than 10 percent to 100 percent, Vreeland explains, with 50 percent being about average.
On his two study sites -- one a mostly agricultural, 200-square-mile area in eastern Centre County called Penns Valley, the other a 100-square-mile "big woods" tract in Elk, Cameron and Clearfield counties known as Quehanna Wild Area -- predation varies widely.
In Quehanna, which is predominantly mature forest largely uninterrupted by roads, dwellings or other trappings of civilization, predators kill many fawns. In Penns Valley, Vreeland notes, predation is much less common and fawn survival is higher overall.
"Fifty percent of the fawns we collared in the Quehanna area were killed by predators last year, compared to just 8 percent at the Penns Valley site," he says. "Habitat in Quehanna is poorer for deer in terms of both food and cover. There are fewer humans and interference, and more predators because deer have overbrowsed the trees and other plants. There are fewer hiding places and alternative food sources for predators."
It is unclear whether bear predation on fawns is increasing, Vreeland admits, because his study is the first in-depth look at Pennsylvania's fawn population done in three decades. Because radio telemetry technology was unavailable for previous studies, this research is more thorough than past efforts, although it is sometimes still impossible from evidence left at kill sites to determine what predator killed a fawn.
"There clearly are more bears now in Pennsylvania," Vreeland explains. "The population has tripled to 9,000 or 10,000. Bears are opportunistic predators -- they eat what they stumble upon. They are omnivores and will eat everything from carrion to nuts and berries to live animals. If they stumble upon a fawn sleeping in the middle of the night, they are going to whack it."
He thinks many people have trouble believing Pennsylvania's black bears kill lots of fawns. "We run into people at both of our study sites who are adamant that we have a coyote problem and that we have too many coyotes that are killing too many deer," he says. "But when we tell them that bears in this state are killing at least as many fawns as coyotes, they don't want to believe it."
The study of fawn mortality started in May 2000 and will conclude in April 2002. Once a fawn is collared, researchers monitor it sometimes daily and at least weekly, tracking movement and survival. The collars fall off when cotton stitches rot after a year or so. They are designed to grow with fawns and sit comfortably on a deer's neck. The battery lasts a year or more.
When a collar signals that a fawn has died, the researchers locate the collar and examine evidence at the kill site -- such as tracks, hair and matted vegetation (bears like to wallow during or after a big meal, perhaps from contentment) -- to determine what killed the young deer.
The study has involved 18 Game commission employees in each of the two years. The staff is a combination of part-time, full-time and temporary employees who are students. Many have graduated.
A special Web site allows the public to keep track of Penn State fawn research progress. Results are regularly updated in the study journal at http://sites.state.pa.us/PA_Exec/PGC/deer/fawn/fwnintro.htm.
Researchers were surprised to learn two other things about fawns. First, it doesn't seem unusual for them to travel long distances. One covered four miles in a few hours. And for unknown reasons, between 10 and 30 percent of fawns are abandoned by their mothers. At the Penns Valley study site, starvation-malnutrition and disease are the two biggest killers of fawns, according to Vreeland.
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EDITORS: Justin Vreeland can be reached at 814-865-3972 or e-mail jkv104@psu.edu.
Contact:
Jeff Mulhollem jjm29@psu.edu 814-863-2719 814-865-1068 fax