Post by Bobcat on Nov 10, 2003 8:40:08 GMT -5
More Yellowstone elk calves' deaths caused by bears than wolves
By SCOTT McMILLION, Chronicle Staff Writer
Predators are killing almost two-thirds of the elk calves born in Yellowstone National Park even before winter hits, the preliminary results of a study have shown.
That is almost three times the death rate found in a similar study in the 1980s, before wolves were reintroduced to the park.
However, the lion's share of calf deaths came from grizzly and black bears, which killed almost four times as many elk calves as wolves did, the study says.
P. J. White, a wildlife biologist for the National Park Service, cautioned that the results are preliminary. The study will last for three years and only one season's worth of data has been gathered.
"It's hard to say what the average will be over three years," added Glenn Plumb, a park supervisory biologist. "But they saw what they saw."
While the study sheds some light on the contentious debate over the impact wolves have on the park's elk, it doesn't illuminate the entire debate.
Some hunters, outfitters and politicians have blamed wolves for declining elk numbers. Park scientists maintain there are a variety of factors, like drought and other predators, at play in the 2.2 million-acre park.
"I'm real skeptical about all their reports," said Bill Hoppe, a Jardine outfitter. "We've had grizzly bears forever, and bad winters, and the elk have always done OK."
The elk herd began declining in 1996 after wolves were reintroduced, Hoppe said, "and it's gotten smaller ever since."
Researchers began work in May, capturing 51 elk calves, usually within their first three days of life, and attaching ear tags that emit electronic signals. When a calf hasn't moved for four hours, it indicates that animal probably is dead.
"It's essentially a race to the carcass then," White said in an interview, "so we can get there before other predators and scavengers come in."
Field workers then gather hair and scat, analyze bite marks and assess other data to determine how the calves died.
One transmitter malfunctioned, leaving 50 animals in the study.
Of that number, predators killed 31 and three died from unknown causes as of Oct. 6.
Bears killed 19 calves, or 61 percent. Grizzlies killed 10, black bears killed five and bears of undetermined species killed the other four.
Wolves killed five, coyotes killed three and a lion and a wolverine each killed one. Either a bear or wolves -- researchers weren't sure which -- killed two more.
Total the numbers and it shows that 62 percent of the 50 calves fell to predators in their first four months of life, most within the first 30 days.
The project is set up to mimic as closely as possible a study done between 1987 and 1990, one that was conducted in part so scientists would have a baseline from which to measure wolf impacts.
Wolves were reintroduced in 1995 and 1996.
For the early study, biologists attached transmitters to 127 elk calves. Over four years, 28 of them, or 22 percent, fell to predators during the first summer of their lives.
Of that number, grizzlies killed 11, black bears killed one, and undetermined bear species killed three, for a total of 15.
That means bears accounted for 53 percent of all predator kills in the earlier study, compared to 61 percent in the recent study.
Kills by coyotes have dropped. They killed 11 calves, or 28 percent, in the early study, compared to three, or 10 percent, in the recent study.
An eagle killed one in the early study and lions killed one calf in each study.
Typically, White explained, bears kill elk calves early in the season. They tend to do it by spotting a lone female elk, chasing her from a calf, then systematically searching the brush that hides the calf.
"They're almost gridding the area," White said. "They're remarkably efficient."
The early study, led by researcher Francis Singer, found that "summer losses of elk calves, mostly due to predation, were roughly equivalent to winter losses."
If that pattern continues, it could help explain the low proportion of calves that have been surviving their first year for several years now. That proportion, known as the "recruitment rate," has been about 10 percent for the past few years.
A recruitment rate of about 30 percent, averaged over several years, is considered necessary to maintain a herd size.
Wolves likely will begin to kill more calves now that winter is arriving.
"About 40 percent of what wolves kill in the winter is elk calves," said Doug Smith, the park's top wolf biologist.
Many people have speculated that, in addition, wolves have been gobbling lots of newborn elk. But the preliminary study results show the number is relatively low.
Smith said he expected to see a higher percentage of wolf kills.
"P.J's results are striking," Smith said. "I thought wolves had a bigger piece of the pie."
Hoppe, the outfitter, noted that wolves, unlike bears, kill elk year-round. He predicted that few of the calves in the study will be alive by next spring.
The scientists running the study are hoping to learn whether the number of calves killed by wolves is "additive" or "compensatory" to the overall death toll.
If it's additive, it means wolves are increasing the death toll. If it's compensative, it means wolves are killing calves that would have been killed by another predator or in some other way.
One intriguing part of the study is the big drop in coyote predation.
In the early study, coyotes killed as many calves as grizzly bears.
But since wolves were reintroduced, coyote numbers have fallen by 50 percent or more in key wolf habitat, some studies show.
The Yellowstone mixture is a complicated one.
"Grizzly bears have increased, coyotes have decreased and wolves have been added," Smith said.
And winter has yet to play a role in the study.
Hoppe said he watched from his Jardine home while 11 wolves killed and ate an elk Thursday. Later, he saw a group of 21 wolves.
"There's just wolves everywhere around here," he said.
By SCOTT McMILLION, Chronicle Staff Writer
Predators are killing almost two-thirds of the elk calves born in Yellowstone National Park even before winter hits, the preliminary results of a study have shown.
That is almost three times the death rate found in a similar study in the 1980s, before wolves were reintroduced to the park.
However, the lion's share of calf deaths came from grizzly and black bears, which killed almost four times as many elk calves as wolves did, the study says.
P. J. White, a wildlife biologist for the National Park Service, cautioned that the results are preliminary. The study will last for three years and only one season's worth of data has been gathered.
"It's hard to say what the average will be over three years," added Glenn Plumb, a park supervisory biologist. "But they saw what they saw."
While the study sheds some light on the contentious debate over the impact wolves have on the park's elk, it doesn't illuminate the entire debate.
Some hunters, outfitters and politicians have blamed wolves for declining elk numbers. Park scientists maintain there are a variety of factors, like drought and other predators, at play in the 2.2 million-acre park.
"I'm real skeptical about all their reports," said Bill Hoppe, a Jardine outfitter. "We've had grizzly bears forever, and bad winters, and the elk have always done OK."
The elk herd began declining in 1996 after wolves were reintroduced, Hoppe said, "and it's gotten smaller ever since."
Researchers began work in May, capturing 51 elk calves, usually within their first three days of life, and attaching ear tags that emit electronic signals. When a calf hasn't moved for four hours, it indicates that animal probably is dead.
"It's essentially a race to the carcass then," White said in an interview, "so we can get there before other predators and scavengers come in."
Field workers then gather hair and scat, analyze bite marks and assess other data to determine how the calves died.
One transmitter malfunctioned, leaving 50 animals in the study.
Of that number, predators killed 31 and three died from unknown causes as of Oct. 6.
Bears killed 19 calves, or 61 percent. Grizzlies killed 10, black bears killed five and bears of undetermined species killed the other four.
Wolves killed five, coyotes killed three and a lion and a wolverine each killed one. Either a bear or wolves -- researchers weren't sure which -- killed two more.
Total the numbers and it shows that 62 percent of the 50 calves fell to predators in their first four months of life, most within the first 30 days.
The project is set up to mimic as closely as possible a study done between 1987 and 1990, one that was conducted in part so scientists would have a baseline from which to measure wolf impacts.
Wolves were reintroduced in 1995 and 1996.
For the early study, biologists attached transmitters to 127 elk calves. Over four years, 28 of them, or 22 percent, fell to predators during the first summer of their lives.
Of that number, grizzlies killed 11, black bears killed one, and undetermined bear species killed three, for a total of 15.
That means bears accounted for 53 percent of all predator kills in the earlier study, compared to 61 percent in the recent study.
Kills by coyotes have dropped. They killed 11 calves, or 28 percent, in the early study, compared to three, or 10 percent, in the recent study.
An eagle killed one in the early study and lions killed one calf in each study.
Typically, White explained, bears kill elk calves early in the season. They tend to do it by spotting a lone female elk, chasing her from a calf, then systematically searching the brush that hides the calf.
"They're almost gridding the area," White said. "They're remarkably efficient."
The early study, led by researcher Francis Singer, found that "summer losses of elk calves, mostly due to predation, were roughly equivalent to winter losses."
If that pattern continues, it could help explain the low proportion of calves that have been surviving their first year for several years now. That proportion, known as the "recruitment rate," has been about 10 percent for the past few years.
A recruitment rate of about 30 percent, averaged over several years, is considered necessary to maintain a herd size.
Wolves likely will begin to kill more calves now that winter is arriving.
"About 40 percent of what wolves kill in the winter is elk calves," said Doug Smith, the park's top wolf biologist.
Many people have speculated that, in addition, wolves have been gobbling lots of newborn elk. But the preliminary study results show the number is relatively low.
Smith said he expected to see a higher percentage of wolf kills.
"P.J's results are striking," Smith said. "I thought wolves had a bigger piece of the pie."
Hoppe, the outfitter, noted that wolves, unlike bears, kill elk year-round. He predicted that few of the calves in the study will be alive by next spring.
The scientists running the study are hoping to learn whether the number of calves killed by wolves is "additive" or "compensatory" to the overall death toll.
If it's additive, it means wolves are increasing the death toll. If it's compensative, it means wolves are killing calves that would have been killed by another predator or in some other way.
One intriguing part of the study is the big drop in coyote predation.
In the early study, coyotes killed as many calves as grizzly bears.
But since wolves were reintroduced, coyote numbers have fallen by 50 percent or more in key wolf habitat, some studies show.
The Yellowstone mixture is a complicated one.
"Grizzly bears have increased, coyotes have decreased and wolves have been added," Smith said.
And winter has yet to play a role in the study.
Hoppe said he watched from his Jardine home while 11 wolves killed and ate an elk Thursday. Later, he saw a group of 21 wolves.
"There's just wolves everywhere around here," he said.
