Environmental Influences on Dall's Sheep Survival

Kerk, Madelon van de; Arthur, Stephen M.; Bertram, Mark R.; Borg, Bridget L.; Herriges, Jim D; Lawler, James P.; Mangipane, Buck A.; Koizumi, Catherine Lambert; Wendling, Brad; Prugh, Laura R.

doi:10.1002/jwmg.21873

Cited by 9 publications

(11 citation statements)

References 53 publications

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“…Furthermore, an index of green vegetation (NDVI) was positively, but not significantly selected by sheep during summer in LCNPP ( Table 3 ). Similar patterns were reported by van de Kerk et al [ 34 ] who found that maximum summer NDVI was associated with higher lamb survival and Roffler et al [ 38 ] who noted that Dall’s sheep selected intermediate values of NDVI during summer. Mountain sheep move to forage in areas with newly emerged green vegetation with high nutritional content [ 18 , 74 ], and the lack of a strong effect of NDVI on habitat selection during summer could be related to the presence of alpine dwarf evergreen scrub year round [ 73 ] and/or to tradeoffs associated with other ecological needs including security [ 19 ].…”

Section: Discussionsupporting

confidence: 86%

“…Female sheep in LCNPP selected habitat with less snow cover and shallower snow depths during spring and winter, and warmer winters will reduce both of these factors, allowing more and longer access to forage [ 4 , 8 , 33 ]. However, changes in the composition and frequency of precipitation, such as rain-on-snow events and changes in temperature that lead to a higher frequency of freeze-thaw cycles, will increase the cost of movement by sheep and reduce access to forage [ 9 , 33 , 34 , 67 ]. Because of its location near the southern coast of Alaska, LCNPP could be particularly influenced by rain-on-snow events and a higher frequency of freeze-thaw cycles as opposed to regions in the interior of Alaska [ 9 , 34 , 78 ].…”

Section: Discussionmentioning

confidence: 99%

“…Recent work has suggested that climate can exert a strong influence on the behavior and demography of Dall’s sheep, but many questions remain. Across Alaska, a decline in recruitment of lambs and survival of adults is strongly affected by spring weather, and the magnitude of the effect varies across latitudes [ 32 – 34 ]. In the Northern Richardson Mountains of the Yukon in Canada, multiple factors such as potential competition for resources with other herbivores, predation, and emerging diseases could be contributing to observed population declines, however, the effects of documented increases in temperature and precipitation related to climate change remain unknown [ 30 ].…”

Section: Introductionmentioning

confidence: 99%

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Habitat selection by Dall’s sheep is influenced by multiple factors including direct and indirect climate effects

et al. 2021

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Arctic and boreal environments are changing rapidly, which could decouple behavioral and demographic traits of animals from the resource pulses that have shaped their evolution. Dall’s sheep (Ovis dalli dalli) in northwestern regions of the USA and Canada, survive long, severe winters and reproduce during summers with short growing seasons. We sought to understand the vulnerability of Dall’s sheep to a changing climate in Lake Clark National Park and Preserve, Alaska, USA. We developed ecological hypotheses about nutritional needs, security from predators, energetic costs of movement, and thermal shelter to describe habitat selection during winter, spring, and summer and evaluated habitat and climate variables that reflected these hypotheses. We used the synoptic model of animal space use to estimate parameters of habitat selection by individual females and calculated likelihoods for ecological hypotheses within seasonal models. Our results showed that seasonal habitat selection was influenced by multiple ecological requirements simultaneously. Across all seasons, sheep selected steep rugged areas near escape terrain for security from predators. During winter and spring, sheep selected habitats with increased forage and security, moderated thermal conditions, and lowered energetic costs of movement. During summer, nutritional needs and security influenced habitat selection. Climate directly influenced habitat selection during the spring lambing period when sheep selected areas with lower snow depths, less snow cover, and higher air temperatures. Indirectly, climate is linked to the expansion of shrub/scrub vegetation, which was significantly avoided in all seasons. Dall’s sheep balance resource selection to meet multiple needs across seasons and such behaviors are finely tuned to patterns of phenology and climate. Direct and indirect effects of a changing climate may reduce their ability to balance their needs and lead to continued population declines. However, several management approaches could promote resiliency of alpine habitats that support Dall’s sheep populations.

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Section: Discussionsupporting

confidence: 86%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Habitat selection by Dall’s sheep is influenced by multiple factors including direct and indirect climate effects

et al. 2021

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“…Our dataset however does not include variables pertaining to the quality of vegetation available to ewes in the summer preceding or current to lambing. Both early [93] and more recent work [94] has connected metrics of summer forage quality with both lamb survival rates [93,94] and Dall's sheep productivity [93]. Also beyond the scope of the current study are the effects of interspecific relationships.…”

Section: Plos Onementioning

confidence: 92%

“…Also beyond the scope of the current study are the effects of interspecific relationships. The primary predators of Dall's sheep, coyote (Canis latrans) and golden eagles (Aquila chrysaetos), have been shown to account for less lamb mortality in summers with a high Normalized Difference Vegetation Index (NDVI) [94] and are likely to prey more on Dall's sheep during years with low snowshoe hare numbers [43,45]. To gain a more holistic understanding of Dall's sheep productivity and population dynamics, attention needs to be paid to a wide range of biotic and abiotic factors that are not considered here.…”

Section: Plos Onementioning

confidence: 99%

Seasonal influence of snow conditions on Dall’s sheep productivity in Wrangell-St Elias National Park and Preserve

et al. 2021

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Dall’s sheep (Ovis dalli dalli) are endemic to alpine areas of sub-Arctic and Arctic northwest America and are an ungulate species of high economic and cultural importance. Populations have historically experienced large fluctuations in size, and studies have linked population declines to decreased productivity as a consequence of late-spring snow cover. However, it is not known how the seasonality of snow accumulation and characteristics such as depth and density may affect Dall’s sheep productivity. We examined relationships between snow and climate conditions and summer lamb production in Wrangell-St Elias National Park and Preserve, Alaska over a 37-year study period. To produce covariates pertaining to the quality of the snowpack, a spatially-explicit snow evolution model was forced with meteorological data from a gridded climate re-analysis from 1980 to 2017 and calibrated with ground-based snow surveys and validated by snow depth data from remote cameras. The best calibrated model produced an RMSE of 0.08 m (bias 0.06 m) for snow depth compared to the remote camera data. Observed lamb-to-ewe ratios from 19 summers of survey data were regressed against seasonally aggregated modelled snow and climate properties from the preceding snow season. We found that a multiple regression model of fall snow depth and fall air temperature explained 41% of the variance in lamb-to-ewe ratios (R2 = .41, F(2,38) = 14.89, p<0.001), with decreased lamb production following deep snow conditions and colder fall temperatures. Our results suggest the early establishment and persistence of challenging snow conditions is more important than snow conditions immediately prior to and during lambing. These findings may help wildlife managers to better anticipate Dall’s sheep recruitment dynamics.

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Collaborative wildlife–snow science: Integrating wildlife and snow expertise to improve research and management

et al. 2022

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For wildlife inhabiting snowy environments, snow properties such as onset date, depth, strength, and distribution can influence many aspects of ecology, including movement, community dynamics, energy expenditure, and forage accessibility. As a result, snow plays a considerable role in individual fitness and ultimately population dynamics, and its evaluation is, therefore, important for comprehensive understanding of ecosystem processes in regions experiencing snow. Such understanding, and particularly study of how wildlife–snow relationships may be changing, grows more urgent as winter processes become less predictable and often more extreme under global climate change. However, studying and monitoring wildlife–snow relationships continue to be challenging because characterizing snow, an inherently complex and constantly changing environmental feature, and identifying, accessing, and applying relevant snow information at appropriate spatial and temporal scales, often require a detailed understanding of physical snow science and technologies that typically lie outside the expertise of wildlife researchers and managers. We argue that thoroughly assessing the role of snow in wildlife ecology requires substantive collaboration between researchers with expertise in each of these two fields, leveraging the discipline‐specific knowledge brought by both wildlife and snow professionals. To facilitate this collaboration and encourage more effective exploration of wildlife–snow questions, we provide a five‐step protocol: (1) identify relevant snow property information; (2) specify spatial, temporal, and informational requirements; (3) build the necessary datasets; (4) implement quality control procedures; and (5) incorporate snow information into wildlife analyses. Additionally, we explore the types of snow information that can be used within this collaborative framework. We illustrate, in the context of two examples, field observations, remote‐sensing datasets, and four example modeling tools that simulate spatiotemporal snow property distributions and, in some cases, evolutions. For each type of snow data, we highlight the collaborative opportunities for wildlife and snow professionals when designing snow data collection efforts, processing snow remote sensing products, producing tailored snow datasets, and applying the resulting snow information in wildlife analyses. We seek to provide a clear path for wildlife professionals to address wildlife–snow questions and improve ecological inference by integrating the best available snow science through collaboration with snow professionals.

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Environmental Influences on Dall's Sheep Survival

Cited by 9 publications

References 53 publications

Habitat selection by Dall’s sheep is influenced by multiple factors including direct and indirect climate effects

Habitat selection by Dall’s sheep is influenced by multiple factors including direct and indirect climate effects

Seasonal influence of snow conditions on Dall’s sheep productivity in Wrangell-St Elias National Park and Preserve

Collaborative wildlife–snow science: Integrating wildlife and snow expertise to improve research and management

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