Environmental Influences on Dall's Sheep Survival

• Published in: The Journal of Wildlife Management
• Main Authors: Van de Kerk, Madelon, Arthur, Stephen, Bertram, Mark, Borg, Bridget, Herriges, Jim, Lawler, James, Mangipane, Buck, Lambert Koizumi, Catherine, Wendling, Brad, Prugh, Laura
• Other Authors: NASA ABoVE
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2020
• Subjects: Arctic; Canada; Climate change; Alaska; Aquila chrysaetos
• Online Access: http://dx.doi.org/10.1002/jwmg.21873; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjwmg.21873; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jwmg.21873; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/jwmg.21873

ABSTRACT Understanding how species respond to environmental conditions can assist with conservation strategies and harvest management, especially in arctic and boreal regions that are experiencing rapid climate change. Although climatic influences on species distributions have been studied, broad‐scale effects of climate on survival are less well known. We examined the interactive effects of meteorological and remotely sensed environmental variables on survival of Dall's sheep ( Ovis dalli dalli ) lambs and adults by synthesizing radio‐telemetry data across their range. We used data from 9 studies of adult sheep and 2 studies of lambs that were conducted between 1997 and 2012 at sites spanning the species' range in Alaska, USA, and northwestern Canada. We obtained environmental variables throughout the range of Dall's sheep, including the normalized difference vegetation index (NDVI) from optical remote sensing, freeze‐thaw frequency (FTF) from passive microwave remote sensing, and gridded climate variables such as snow water equivalent, temperature, and precipitation. We used Cox proportional hazard regression to investigate the effects of environmental variables recorded during summer, winter, and the previous winter on annual survival rates of Dall's sheep lambs and adults. Summer NDVI was the most influential environmental factor affecting lamb survival, with improved lamb survival occurring in years with a high maximum NDVI. Also, lamb predation by coyotes ( Canis latrans ) and golden eagles ( Aquila chrysaetos ) decreased substantially with increasing NDVI. The previous winter FTF had the strongest effect on adult survival, with decreased survival occurring after winters with high FTF. In addition, these remotely sensed environmental factors interacted with meteorological factors to affect survival, such that effects of winter temperature depended on summer NDVI and winter FTF. Warm winters increased lamb survival only when preceded by summers with high NDVI, and warm winters increased adult survival only ...