Standing their ground
Jasper's bighorn sheep face the danger of predators, highway traffic, invasive weeds and drought. But so far, they are free of the contagious lung diseases decimating wild sheep in the western U.S.
By Dick Dekker
A bighorn sheep near the road between Banff and Lake Louise on November 23, 2009.
Compared to the elusive grizzly or woodland caribou, bighorn sheep seldom seem newsworthy, although it is the most common and iconic mammal of our Rocky Mountain national parks.Familiar to every visitor, herds of sheep hang out beside the Yellowhead Highway. After years of protection from hunting in the park, therams and ewes have lost their fear of humans.
They may even make use of us as an involuntary shield against their many natural enemies. Predators such as wolves and cougars tend to shy away from roadsides where the bighorns concentrate.But just in case a four-legged foe might try something, the sharp-eyed sheep instinctively stay within a quick dash from steep escape terrain. Equipped by mother nature with hollow suction hoofs, a defenceless lamb can make a stand on a rocky pinnacle where a slavering wolf finds no footing.
Historically, Jasper's sheep population has gone through major fluctuations that are intertwined with the ups and downs of the region's elk.In 1907, when Jasper National Park was established, the majestic elk, like all other big-game animals, had been practically exterminated in western Alberta.Elk were reintroduced to the park in the 1920s with stock obtained from Yellowstone. By the mid-1940s, they had increased to about 3,000 and were competing for grass with the park's sheep on shared winter ranges. In order to reduce grazing pressure, park wardens culled elk herds by shooting several hundred cows each winter.
Nevertheless, forage conditions continued to deteriorate and, in the mid-1960s, provincial biologist John Stelfox predicted that a massive sheep die-off was imminent, triggered by malnutrition. In particular, he feared the outbreak of contagious disease.Fortunately, Stelfox's realistic scenario failed to unfold because nature interfered, coupled with a watershed change in public attitudes toward wolves.Paradoxically, both Stelfox and the park wardens had supported the old policy that predators were not welcome. Wolves were shot on sight, and poisoning campaigns were routine on Jasper's boundaries, sometimes even inside the park. By the mid-1960s, after the strychnine years finally ended, the wolves staged a big comeback.
They did so with a vengeance, so to speak, for their prey had reached unprecedented levels and the elk were weakened by a series of extremely cold winters.The killer year was 1974 when the Jasper weather station reported an accumulation of 90 centimetres of snow in late January, with over half a metre still on the ground at the end of March. Following the combined effect of heavy predation superimposed on starvation, elk numbers plunged to less than one third of former estimates. Sheep declined as well, but the threat of disease had lifted.
In combination with environmental factors, the return of the wolf had clearly been a pivotal event in bringing the park's elk and sheep back to more sustainable levels. Up to this day, Jasper's herbivores and carnivores have been allowed to find their own equilibrium in a dynamic balance between grass and meat.
The park's sheep population appears to have been quite stable from 1967 to 1987. An aerial survey flown by Stelfox along 20 mountain ranges in 1967 produced a total estimate of 2,011 sheep. Twenty years later, park wardens flew the same ranges and tallied 2,278.
Craving the freshest greens, the majority of bighorns spend the summer months on high alpine slopes. In these lofty solitudes, the ewes and their newborn spread themselves thinly over a huge range where predators are scarce; denning wolves tend to stay behind in the valleys. As winter approaches, the sheep descend to montane habitats, to traditional locations which have to meet their twin requirements of food and safety.
In the thickly forested Rocky Mountains, suitable winter range for sheep is spotty. They prefer open, grassy slopes, allowing a wide view so that wolves can be discovered in time for a safe retreat to a nearby cliff. Some of the best sites are near the main highway, at Disaster Point, at Sulphur Springs, and just east of the townsite across from the turnoff to Maligne Lake.
The sheep's habit of licking road salt on the busy Yellowhead, which carries about 4,000 vehicles per day, comes at the risk of vehicle collisions. On average, 100 hoofed animals die each year on the pavement, and an additional fifty are killed on the CN rails that transect the park's main valley. The month of January, 2011 was particularly bad for sheep: on the 17th, a mixed group of ewes and rams was hit at Disaster Point, probably by a transport truck that never bothered to stop. And on the 13th, a band of six mature rams was destroyed by a train.
Away from the park's dangerous traffic corridor, other traditional sheep wintering sites are on the opposite rim of the wide Athabasca valley near the confluence of the Snaring and Snake Indian Rivers. As a volunteer wildlife researcher, and in co-operation with the warden service, I have had the opportunity to survey two sites over a period of 30 winters. Site One was inhabited by a band of mature rams as well as varying numbers of ewes; Site Two was the exclusive winter home for ewes, yearlings, and lambs. Often accompanied by a fellow observer, I visited the study area on foot once or twice per month between October and March. Each morning and evening we spent about one hour on a lookout hill to scan the semi-open slopes through binoculars or a telescope, counting the sheep and all other large mammals seen.
In this relatively remote corner of the park, there has been little human disturbance; no tourist developments, no road building, no industrial forestry, and no oil exploration. Furthermore, during winter there is no access for unauthorized vehicles, ATV's or snowmobiles. These restrictions are to the credit of Parks Canada's policy of preserving the region's ecological integrity.
One would expect that long-term habitat protection of this sort should result in a stable population of its wildlife, including the sheep. But that did not prove to be the case. Surprisingly, we recorded major declines at both localities. On Site One, the ewes declined from year to year and became totally absent after 15 winters, while the ram band dropped from an average of 18 members in the first 20 years to eleven in the next five years. On Site Two, the ewe band, which varied from 36-46 members during the first 20 years, dropped to 14 in 2008-2010. What could have been the cause?
A keen reader will ask: What about predators? Didn't the area in question abound in wolves and other carnivores? Yes, it did indeed. And their role in the sheep decline was a major focus of our long-term census. The notion that predators regulate, depress, or even decimate prey species is not new, particularly when it concerns the wolf, the ancient nemesis of the herdsman and the competitor for hunters. Many field studies have been and are being conducted in Canada and the United States to find answers about the impact of wolf predation on the numbers and behaviour of herbivores.
Despite the fact that both wolves and bighorns are common in Jasper Park, their direct interaction has seldom been witnessed first-hand by park wardens and biologists. During the 30-year study, we only saw one attack in detail. A single wolf which had been eyeballing a band of 26 ewes standing in a tight group some 80 metres higher on an open slope, suddenly sprinted upward. The band split into two and one group ran down, bypassing the charging wolf, which turned in pursuit. Just before he could seize his prey, the sheep disappeared over the edge of a cliff below the hillside. After three similar attacks, all sheep managed to reach safety.
In another failed attack, photographed near Medicine Lake, a black wolf raced down a steep slope in pursuit of several fleeing ewes and lambs. They managed to escape by a hair's breath, while the wolf slipped and fell partway down the rocks. Wolves are by no means rare in the area we monitored. Most winters, the territorial wolf pack included seven or eight members, and we found fresh tracks on an almost daily basis. However, during our 30-year study only two mature rams were known to have been killed by wolves, which we saw feeding on the remains.
Apparently, these unlucky rams had been intercepted on their flight to the cliff. Additional evidence that sheep can cope quite well with wolves comes from several studies of wolf predation conducted in both Jasper and Banff. Of hundreds of wolf kills examined by researchers, less than 10 per cent were sheep, with the vast majority of victims being deer, elk, and moose. The proportional difference is all the more revealing considering that the bighorn is the most common hoofed mammal in both national parks.
Yet, wolves do play a critical role in sheep population dynamics because the risk of predation forces the band to stay close to an escape cliff, and because of this restriction the safest terrain close to the cliff soon becomes overgrazed. In the absence of wolves, the sheep could have multiplied and spread out to forage over a wider range without the need for a rocky retreat.
Another, and perhaps more dangerous predator of sheep is the cougar, which is common but rarely seen in Jasper's main valley. In Alberta, quite a number of cougars have been captured, fitted with radio-telemetry collars and closely followed. Their main prey was found to be deer. However, as stated by zoologist Marco Festa-Bianchet, individual cougars that specialize in preying on sheep could potentially wipe out small local herds. In the Jasper study area, we occasionally spotted a cougar or found its tracks.
A sheep predator that is generally more common than either wolf or cougar is the coyote. Quick and agile, coyotes can grab a lamb before the band has spotted the danger. They have also been known to kill mature ewes. Coyote occurrence on the sheep hills of the Athabasca valley has apparently declined over our 30-year study. Coyote sightings dropped from one for every five days of observation to less than one for every 33 days. The main reason for their scarcity probably has to do with their bigger canid cousin. Wolves are known to keep coyote numbers down.
Despite the mortal danger posed by three species of predators, proof that the local ram band was quite capable of taking care of itself was illustrated by the fact that their number usually stayed the same from late January to the end of March. How then to explain the eventual decline on both sheep ranges?
The answer has to do with environmental deterioration. By 1993, we discovered that 20 to 40 per cent of Site One had become covered with an invasive weed. Originating from Central Europe, its scientific label is Salsola kali. The common name is Tumble Weed or Russian Thistle, well-known to westerners. On livestock ranges the plant is considered an indicator of overgrazing. When young, the seedlings are palatable, but over summer the small leaves become brittle and the plant turns into a dense ball of thorns that can be spread by the wind.
The thistle infestation began when Site One was frequented by up to 40 ewes. Interestingly, a decade after the departure of the ewes, grazing pressure became less and the thistles were gradually replaced by native grasses. By 2006, the range appeared to have recovered until a new and perhaps even more serious threat arrived: drought. Data from Environment Canada show that Jasper's annual precipitation for the years 2001-2004 averaged 430 millimetres, well below the 35-year mean of 569 mm. During these drought years, south-facing Site Two became denuded of vegetation and largely turned to dust. Scraping for plant roots, the ewes aggravated the problem and eventually they all but abandoned the eroding slopes.
It is not clear whether the drop in local sheep numbers is indicative of an overall decline in the total sheep population of Jasper National Park.
After departing their traditional range, the ewes might have gone elsewhere. Their possible return would depend on summer rains that are badly needed for a greening of the hills. At the end of our 30-year census the picture was bleaker than ever. In 2008 and 2009, annual precipitation was down to 306 and 194 mm, the lowest values recorded since 1971. What the future will bring is an fascinating question for continued observation.
The good news is that Jasper's bighorns have thus far been free from contagious lung diseases, which have been a serious concern for provincial sheep biologists in southwestern Alberta. Based on information provided by William Wishart, Dr. Marco Festa-Bianchet, and University of Calgary professor Kathreen Ruckstuhl, major outbreaks occurred in 1978, 1985, and 2000 due to pneumonia.
In 1983 almost half the sheep population succumbed in the Waterton-Crowsnest Pass region. The exact source of the bacterial infection is unknown but was thought to be domestic cattle intruding on sheep range.
However, the mode of transmission remains a potential problem in discussions between wildlife managers and ranchers.
The issue of disease in mountain sheep came to the fore again in December 2010, when the U.S. Forest Service announced that eleven bighorn herds in Montana, Nevada, Washington, Wyoming, and Utah were coughing and sneezing. More than one thousand sheep died or had to be culled. The carrier of the lethal pathogen known to cause pneumonia was domestic sheep that had mingled with their wild cousins on public lands. The recent mortalities have added a wave of concern over the future of the West's bighorns.
Recent measures by the U.S. government to phase out or reduce livestock grazing allotments on wildlands were countered by appeals from a coalition of American sheep ranchers, who argued that transmission is not well enough understood to warrant drastic restrictions that may sink their operation.The fortunate fact that livestock related problems have been avoided in the population fluctuations of Jasper's bighorn sheep can in part be credited to their remote location, away from domestic grazing leases, as well as to the presence of predators, such as wolves, which tend to weed out unfit and vulnerable prey.
With an intact large mammal system, Jasper Park is an ecological treasure and a Canadian national heritage site of increasing value as the last remaining wild places of the world are being destroyed at an unprecedented rate.
Dick Dekker, PhD, is an independent wildlife researcher who lives in Edmonton.
He has published several books and research papers on wolves and other wildlife in Jasper National Park based on 45 years of first-hand field observation.
They may even make use of us as an involuntary shield against their many natural enemies. Predators such as wolves and cougars tend to shy away from roadsides where the bighorns concentrate.But just in case a four-legged foe might try something, the sharp-eyed sheep instinctively stay within a quick dash from steep escape terrain. Equipped by mother nature with hollow suction hoofs, a defenceless lamb can make a stand on a rocky pinnacle where a slavering wolf finds no footing.
Historically, Jasper's sheep population has gone through major fluctuations that are intertwined with the ups and downs of the region's elk.In 1907, when Jasper National Park was established, the majestic elk, like all other big-game animals, had been practically exterminated in western Alberta.Elk were reintroduced to the park in the 1920s with stock obtained from Yellowstone. By the mid-1940s, they had increased to about 3,000 and were competing for grass with the park's sheep on shared winter ranges. In order to reduce grazing pressure, park wardens culled elk herds by shooting several hundred cows each winter.
Nevertheless, forage conditions continued to deteriorate and, in the mid-1960s, provincial biologist John Stelfox predicted that a massive sheep die-off was imminent, triggered by malnutrition. In particular, he feared the outbreak of contagious disease.Fortunately, Stelfox's realistic scenario failed to unfold because nature interfered, coupled with a watershed change in public attitudes toward wolves.Paradoxically, both Stelfox and the park wardens had supported the old policy that predators were not welcome. Wolves were shot on sight, and poisoning campaigns were routine on Jasper's boundaries, sometimes even inside the park. By the mid-1960s, after the strychnine years finally ended, the wolves staged a big comeback.
They did so with a vengeance, so to speak, for their prey had reached unprecedented levels and the elk were weakened by a series of extremely cold winters.The killer year was 1974 when the Jasper weather station reported an accumulation of 90 centimetres of snow in late January, with over half a metre still on the ground at the end of March. Following the combined effect of heavy predation superimposed on starvation, elk numbers plunged to less than one third of former estimates. Sheep declined as well, but the threat of disease had lifted.
In combination with environmental factors, the return of the wolf had clearly been a pivotal event in bringing the park's elk and sheep back to more sustainable levels. Up to this day, Jasper's herbivores and carnivores have been allowed to find their own equilibrium in a dynamic balance between grass and meat.
The park's sheep population appears to have been quite stable from 1967 to 1987. An aerial survey flown by Stelfox along 20 mountain ranges in 1967 produced a total estimate of 2,011 sheep. Twenty years later, park wardens flew the same ranges and tallied 2,278.
Craving the freshest greens, the majority of bighorns spend the summer months on high alpine slopes. In these lofty solitudes, the ewes and their newborn spread themselves thinly over a huge range where predators are scarce; denning wolves tend to stay behind in the valleys. As winter approaches, the sheep descend to montane habitats, to traditional locations which have to meet their twin requirements of food and safety.
In the thickly forested Rocky Mountains, suitable winter range for sheep is spotty. They prefer open, grassy slopes, allowing a wide view so that wolves can be discovered in time for a safe retreat to a nearby cliff. Some of the best sites are near the main highway, at Disaster Point, at Sulphur Springs, and just east of the townsite across from the turnoff to Maligne Lake.
The sheep's habit of licking road salt on the busy Yellowhead, which carries about 4,000 vehicles per day, comes at the risk of vehicle collisions. On average, 100 hoofed animals die each year on the pavement, and an additional fifty are killed on the CN rails that transect the park's main valley. The month of January, 2011 was particularly bad for sheep: on the 17th, a mixed group of ewes and rams was hit at Disaster Point, probably by a transport truck that never bothered to stop. And on the 13th, a band of six mature rams was destroyed by a train.
Away from the park's dangerous traffic corridor, other traditional sheep wintering sites are on the opposite rim of the wide Athabasca valley near the confluence of the Snaring and Snake Indian Rivers. As a volunteer wildlife researcher, and in co-operation with the warden service, I have had the opportunity to survey two sites over a period of 30 winters. Site One was inhabited by a band of mature rams as well as varying numbers of ewes; Site Two was the exclusive winter home for ewes, yearlings, and lambs. Often accompanied by a fellow observer, I visited the study area on foot once or twice per month between October and March. Each morning and evening we spent about one hour on a lookout hill to scan the semi-open slopes through binoculars or a telescope, counting the sheep and all other large mammals seen.
In this relatively remote corner of the park, there has been little human disturbance; no tourist developments, no road building, no industrial forestry, and no oil exploration. Furthermore, during winter there is no access for unauthorized vehicles, ATV's or snowmobiles. These restrictions are to the credit of Parks Canada's policy of preserving the region's ecological integrity.
One would expect that long-term habitat protection of this sort should result in a stable population of its wildlife, including the sheep. But that did not prove to be the case. Surprisingly, we recorded major declines at both localities. On Site One, the ewes declined from year to year and became totally absent after 15 winters, while the ram band dropped from an average of 18 members in the first 20 years to eleven in the next five years. On Site Two, the ewe band, which varied from 36-46 members during the first 20 years, dropped to 14 in 2008-2010. What could have been the cause?
A keen reader will ask: What about predators? Didn't the area in question abound in wolves and other carnivores? Yes, it did indeed. And their role in the sheep decline was a major focus of our long-term census. The notion that predators regulate, depress, or even decimate prey species is not new, particularly when it concerns the wolf, the ancient nemesis of the herdsman and the competitor for hunters. Many field studies have been and are being conducted in Canada and the United States to find answers about the impact of wolf predation on the numbers and behaviour of herbivores.
Despite the fact that both wolves and bighorns are common in Jasper Park, their direct interaction has seldom been witnessed first-hand by park wardens and biologists. During the 30-year study, we only saw one attack in detail. A single wolf which had been eyeballing a band of 26 ewes standing in a tight group some 80 metres higher on an open slope, suddenly sprinted upward. The band split into two and one group ran down, bypassing the charging wolf, which turned in pursuit. Just before he could seize his prey, the sheep disappeared over the edge of a cliff below the hillside. After three similar attacks, all sheep managed to reach safety.
In another failed attack, photographed near Medicine Lake, a black wolf raced down a steep slope in pursuit of several fleeing ewes and lambs. They managed to escape by a hair's breath, while the wolf slipped and fell partway down the rocks. Wolves are by no means rare in the area we monitored. Most winters, the territorial wolf pack included seven or eight members, and we found fresh tracks on an almost daily basis. However, during our 30-year study only two mature rams were known to have been killed by wolves, which we saw feeding on the remains.
Apparently, these unlucky rams had been intercepted on their flight to the cliff. Additional evidence that sheep can cope quite well with wolves comes from several studies of wolf predation conducted in both Jasper and Banff. Of hundreds of wolf kills examined by researchers, less than 10 per cent were sheep, with the vast majority of victims being deer, elk, and moose. The proportional difference is all the more revealing considering that the bighorn is the most common hoofed mammal in both national parks.
Yet, wolves do play a critical role in sheep population dynamics because the risk of predation forces the band to stay close to an escape cliff, and because of this restriction the safest terrain close to the cliff soon becomes overgrazed. In the absence of wolves, the sheep could have multiplied and spread out to forage over a wider range without the need for a rocky retreat.
Another, and perhaps more dangerous predator of sheep is the cougar, which is common but rarely seen in Jasper's main valley. In Alberta, quite a number of cougars have been captured, fitted with radio-telemetry collars and closely followed. Their main prey was found to be deer. However, as stated by zoologist Marco Festa-Bianchet, individual cougars that specialize in preying on sheep could potentially wipe out small local herds. In the Jasper study area, we occasionally spotted a cougar or found its tracks.
A sheep predator that is generally more common than either wolf or cougar is the coyote. Quick and agile, coyotes can grab a lamb before the band has spotted the danger. They have also been known to kill mature ewes. Coyote occurrence on the sheep hills of the Athabasca valley has apparently declined over our 30-year study. Coyote sightings dropped from one for every five days of observation to less than one for every 33 days. The main reason for their scarcity probably has to do with their bigger canid cousin. Wolves are known to keep coyote numbers down.
Despite the mortal danger posed by three species of predators, proof that the local ram band was quite capable of taking care of itself was illustrated by the fact that their number usually stayed the same from late January to the end of March. How then to explain the eventual decline on both sheep ranges?
The answer has to do with environmental deterioration. By 1993, we discovered that 20 to 40 per cent of Site One had become covered with an invasive weed. Originating from Central Europe, its scientific label is Salsola kali. The common name is Tumble Weed or Russian Thistle, well-known to westerners. On livestock ranges the plant is considered an indicator of overgrazing. When young, the seedlings are palatable, but over summer the small leaves become brittle and the plant turns into a dense ball of thorns that can be spread by the wind.
The thistle infestation began when Site One was frequented by up to 40 ewes. Interestingly, a decade after the departure of the ewes, grazing pressure became less and the thistles were gradually replaced by native grasses. By 2006, the range appeared to have recovered until a new and perhaps even more serious threat arrived: drought. Data from Environment Canada show that Jasper's annual precipitation for the years 2001-2004 averaged 430 millimetres, well below the 35-year mean of 569 mm. During these drought years, south-facing Site Two became denuded of vegetation and largely turned to dust. Scraping for plant roots, the ewes aggravated the problem and eventually they all but abandoned the eroding slopes.
It is not clear whether the drop in local sheep numbers is indicative of an overall decline in the total sheep population of Jasper National Park.
After departing their traditional range, the ewes might have gone elsewhere. Their possible return would depend on summer rains that are badly needed for a greening of the hills. At the end of our 30-year census the picture was bleaker than ever. In 2008 and 2009, annual precipitation was down to 306 and 194 mm, the lowest values recorded since 1971. What the future will bring is an fascinating question for continued observation.
The good news is that Jasper's bighorns have thus far been free from contagious lung diseases, which have been a serious concern for provincial sheep biologists in southwestern Alberta. Based on information provided by William Wishart, Dr. Marco Festa-Bianchet, and University of Calgary professor Kathreen Ruckstuhl, major outbreaks occurred in 1978, 1985, and 2000 due to pneumonia.
In 1983 almost half the sheep population succumbed in the Waterton-Crowsnest Pass region. The exact source of the bacterial infection is unknown but was thought to be domestic cattle intruding on sheep range.
However, the mode of transmission remains a potential problem in discussions between wildlife managers and ranchers.
The issue of disease in mountain sheep came to the fore again in December 2010, when the U.S. Forest Service announced that eleven bighorn herds in Montana, Nevada, Washington, Wyoming, and Utah were coughing and sneezing. More than one thousand sheep died or had to be culled. The carrier of the lethal pathogen known to cause pneumonia was domestic sheep that had mingled with their wild cousins on public lands. The recent mortalities have added a wave of concern over the future of the West's bighorns.
Recent measures by the U.S. government to phase out or reduce livestock grazing allotments on wildlands were countered by appeals from a coalition of American sheep ranchers, who argued that transmission is not well enough understood to warrant drastic restrictions that may sink their operation.The fortunate fact that livestock related problems have been avoided in the population fluctuations of Jasper's bighorn sheep can in part be credited to their remote location, away from domestic grazing leases, as well as to the presence of predators, such as wolves, which tend to weed out unfit and vulnerable prey.
With an intact large mammal system, Jasper Park is an ecological treasure and a Canadian national heritage site of increasing value as the last remaining wild places of the world are being destroyed at an unprecedented rate.
Dick Dekker, PhD, is an independent wildlife researcher who lives in Edmonton.
He has published several books and research papers on wolves and other wildlife in Jasper National Park based on 45 years of first-hand field observation.
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