Temporal environmental variation imposes changing selection pressures that can result in multiple fitness optima occurring over time. In an effort to meet these changing fitness optima, an individual may express multiple trait values in the form of phenotypic flexibility (i.e., the ability to reversibly modify a trait value). Phenotypic flexibility provides an individual with repeated opportunities to match its phenotype to environmental conditions across its lifetime, and is predicted to evolve in environments characterized by frequent and predictable variation. In their latest study titled "Temperature heterogeneity correlates with intraspecific variation in physiological flexibility in a small endotherm",  Dr. Maria Stager and her collaborators tested this prediction by integrating surveys of population genetic and physiological variation with thermal acclimation experiments and indices of environmental heterogeneity in the Dark-eyed Junco. They found that Junco populations respond differentially to thermal cues in the field, and that temperature variability may be driving these patterns of intraspecific variation in thermogenic capacity. Altogether, these results highlight the importance of phenotypic flexibility for coping with environmental change. Beautiful work!