Dall's Sheep - Life in the Mountains is Changing
Masters of the Mountains:
Dall’s sheep, a subspecies of thin-horn sheep, are an icon of northern mountainous landscapes. These completely white sheep only occur in alpine pockets of northwest North America, extending from B.C., through the Yukon/NWT, and into Alaska. The majority of their global population, estimated at less than 110,000, occurs mostly in the Yukon and Alaska. They are almost entirely subarctic and are relatively rare compared to other ungulates. These sheep have evolved to endure extreme cold, persistent snow, sparse food, precarious terrain, and multiple predators. Playing an integral role in their ecosystem, Dall’s sheep are also of great importance to the past and present culture of Indigenous peoples and are highly valued by hunters and wildlife enthusiasts.
Naturally Resilient:
Dall’s sheep naturally go through population ups and downs, regulated by a variety of factors. Predation from coyotes, golden eagles, grizzly bears, and wolves – in addition to subsistence hunting by Indigenous peoples – have always played a role in the evolution of Dall’s sheep. Predation on its own has not been linked to serious, long-lasting sheep declines, likely due to their superb adaptations for rugged habitat. In the last century, direct and indirect effects of anthropogenic activities such as sport hunting, aircraft noise, construction/use, and backcountry recreation have become relatively new stressors for sheep. Although, nowadays the negative effects of these disturbances can often be mitigated through landscape management tools such as regulations and protected areas. In areas where hunting is allowed, restrictions exist to ensure only mature, full curl rams are legal to shoot. Additionally, parks encompass large swaths of Dall’s sheep habitat across their range, naturally managing impacts to sheep within their boundaries by regulating motorized access, land use, and limiting or prohibiting sport hunting. However, parks, protected areas, and regulations do not stop changing environmental conditions associated with climate change.
Climate Change Challenges:
Research is showing freeze-thaw and rain-on-snow events are happening more often, in addition to increasing variability in snowpack properties such as depth, density, and seasonal coverage. Warmer winters are responsible for these conditions which create ice crusts on top of the snowpack and can encrust vegetation. As a result, Dall’s sheep are forced to spend extra energy while foraging and travelling during the time of year when they are already nutritionally deprived. Recent studies have found sheep survival rates were higher when winter temperatures were mild, but once temperatures were too high, freeze-thaw events and winter rain became more common, which in turn reduced adult sheep survival. In another study, lamb survival was linked to the timing of spring snow melt; when snow persisted longer in the spring, lamb survival was poor. Results from some Yukon sheep surveys have shown that low temperatures in fall and/or spring have been correlated with lower-than-average lamb counts per 100 nursery sheep. Nursery sheep include ewes, yearlings, and rams younger than two years old. This ratio of lambs per 100 nursery sheep, known as “recruitment”, by biologists, is a standard index for monitoring ungulate species. Tracking recruitment ratios over time provides biologists with insights into long term population health, and the current trends are concerning.
An Indicator Species:
Within the last decade, range-wide Dall’s sheep surveys have found evidence of population instability and in some cases, serious declines. These mountain sheep have proven their resilience to predation, hunting, and other human-caused impacts in the past. However, climate change may be impacting sheep in ways they haven’t had time to adapt to yet. We know the climate is changing faster in the north compared to other parts of the world, particularly in winter and at high altitudes. Given their excellent adaptations for life in these northern, cold, high places, when Dall’s sheep struggle it is a signal of change happening at an ecosystem level, affecting all the plants, animals, and natural processes within it.
Read MoreDall’s sheep, a subspecies of thin-horn sheep, are an icon of northern mountainous landscapes. These completely white sheep only occur in alpine pockets of northwest North America, extending from B.C., through the Yukon/NWT, and into Alaska. The majority of their global population, estimated at less than 110,000, occurs mostly in the Yukon and Alaska. They are almost entirely subarctic and are relatively rare compared to other ungulates. These sheep have evolved to endure extreme cold, persistent snow, sparse food, precarious terrain, and multiple predators. Playing an integral role in their ecosystem, Dall’s sheep are also of great importance to the past and present culture of Indigenous peoples and are highly valued by hunters and wildlife enthusiasts.
Naturally Resilient:
Dall’s sheep naturally go through population ups and downs, regulated by a variety of factors. Predation from coyotes, golden eagles, grizzly bears, and wolves – in addition to subsistence hunting by Indigenous peoples – have always played a role in the evolution of Dall’s sheep. Predation on its own has not been linked to serious, long-lasting sheep declines, likely due to their superb adaptations for rugged habitat. In the last century, direct and indirect effects of anthropogenic activities such as sport hunting, aircraft noise, construction/use, and backcountry recreation have become relatively new stressors for sheep. Although, nowadays the negative effects of these disturbances can often be mitigated through landscape management tools such as regulations and protected areas. In areas where hunting is allowed, restrictions exist to ensure only mature, full curl rams are legal to shoot. Additionally, parks encompass large swaths of Dall’s sheep habitat across their range, naturally managing impacts to sheep within their boundaries by regulating motorized access, land use, and limiting or prohibiting sport hunting. However, parks, protected areas, and regulations do not stop changing environmental conditions associated with climate change.
Climate Change Challenges:
Research is showing freeze-thaw and rain-on-snow events are happening more often, in addition to increasing variability in snowpack properties such as depth, density, and seasonal coverage. Warmer winters are responsible for these conditions which create ice crusts on top of the snowpack and can encrust vegetation. As a result, Dall’s sheep are forced to spend extra energy while foraging and travelling during the time of year when they are already nutritionally deprived. Recent studies have found sheep survival rates were higher when winter temperatures were mild, but once temperatures were too high, freeze-thaw events and winter rain became more common, which in turn reduced adult sheep survival. In another study, lamb survival was linked to the timing of spring snow melt; when snow persisted longer in the spring, lamb survival was poor. Results from some Yukon sheep surveys have shown that low temperatures in fall and/or spring have been correlated with lower-than-average lamb counts per 100 nursery sheep. Nursery sheep include ewes, yearlings, and rams younger than two years old. This ratio of lambs per 100 nursery sheep, known as “recruitment”, by biologists, is a standard index for monitoring ungulate species. Tracking recruitment ratios over time provides biologists with insights into long term population health, and the current trends are concerning.
An Indicator Species:
Within the last decade, range-wide Dall’s sheep surveys have found evidence of population instability and in some cases, serious declines. These mountain sheep have proven their resilience to predation, hunting, and other human-caused impacts in the past. However, climate change may be impacting sheep in ways they haven’t had time to adapt to yet. We know the climate is changing faster in the north compared to other parts of the world, particularly in winter and at high altitudes. Given their excellent adaptations for life in these northern, cold, high places, when Dall’s sheep struggle it is a signal of change happening at an ecosystem level, affecting all the plants, animals, and natural processes within it.
Lambs are able to walk within hours of being born and are quickly building strength and agility in the following weeks.
