Abstract
Color polymorphism is an adaptive strategy in which a species exhibits
multiple color phenotypes in a population. Often times, phenotypes are
variably suited to different environmental conditions which may buffer
the population against variable conditions. Modern climate change is
creating novel selective pressures for many species, especially in
winter habitats. Few studies have quantified the benefits of
polymorphism for allowing species to cope with climate-induced
environmental change. We investigated how color polymorphism mediates
selective pressures in ruffed grouse Bonasa umbellus, a widespread and
winter-adapted bird species of North American forests. Ruffed grouse
display phenotypic variation in plumage color, ranging from red to gray.
Over five winter seasons (2015-2022), we monitored weather conditions,
habitat use, and weekly survival for 94 ruffed grouse to test whether
individuals had lower survival when grouse were phenotypically
mismatched with snow cover (e.g., a gray bird on a snowless landscape or
a red bird in snow). Grouse phenotypically mismatched with snow cover
had lower survival, but only when winter survival rates were lowest.
During winters of lower overall survival, red grouse exhibited higher
survival during snow-free periods, whereas gray grouse had higher
survival when snow was present. We also found that open habitat
negatively impacted survival, regardless of color. While the effect of
phenotypic mismatch was variable among years, it was a stronger
predictor of winter survival than land cover features, suggesting that
snow is an important habitat feature mediating overwinter survival. Our
work offers an advancement in understanding how environmental
variability affects geographic variation in and maintenance of multiple
color phenotypes in seasonally-snow covered environments. Our finding
that interactions between color morph and snow cover are important for
conferring winter survival provides further evidence that color
polymorphism may serve as a buffer against rapidly changing conditions
and a pathway for persistence of polymorphic species.