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.