Implications
Our work adds to a growing body of literature on the importance of snow
for mediating survival and population persistence of winter-adapted
species in northern ecosystems (Petty et al. 2015, Zuckerberg and Pauli
2018, Smith et al. 2022). Phenotypic mismatch with snow presence or
absence appears to impact ruffed grouse winter survival and provides a
possible explanation for the proposed geographic structuring of morph
ratios across the ruffed grouse’s range. It has long been speculated
that morph ratios in grouse covary with latitude and snow season length,
with higher proportions of gray birds in northern areas and more red
individuals in southerly and coastal regions (Bump et al. 1947, Rusch et
al. 2020), but there has been no previous work to formally describe the
potential mechanisms of these patterns.
Investigating drivers of morph-specific survival differences in color
polymorphic species is critical for understanding how species might
adapt to novel environmental conditions such as reduced snow cover in a
rapidly warming climate. Modern climate change has created and will
continue to create novel selective pressures and environmental
conditions for species (Parmesan 2006). For many high-latitude
ecosystems, and specifically the Upper Midwest, climate change has
resulted in earlier snow melt, a reduction in the number of days with
persistent snow cover (Choi et al. 2010), and an overall decrease of
snow cover extent across the Upper Midwest (Andresen et al. 2014).
Climate predictions for the Upper Midwest and Northeastern United States
project these trends will continue in future decades (Notaro et al.
2014, Demaria et al. 2016), and pose a significant threat for
winter-adapted species (Williams et al. 2015). Understanding how snow
cover affects survival for winter-adapted species is crucial to
informing conservation decisions as climate change continues to alter
snow cover duration and extent (Sultaire et al. 2016, Zuckerberg and
Pauli 2018). This is especially true for ruffed grouse, a species
experiencing population declines across the Upper Midwest, specifically
along its southern range boundary in Wisconsin. Our findings may help
inform future conservation actions such as selecting individuals
best-suited for translocations or identifying regions in a species’
distribution where they may be most vulnerable or resilient to shifting
winter conditions (Roulin 2014, Baling et al. 2016, Mills et al. 2018,
Smith et al. 2022).