Phenotypic plasticity co-varies with elevational range in two avian species of elevational migrants in the Himalayas

Montane birds represent a large proportion of global avian biodiversity and are highly sensitive to seasonal climatic shifts. Many montane species undertake elevational migration in response to seasonal climate change, but how they cope with disparate environmental pressures along the elevational gradient is poorly understood. Here, we investigate phenotypic plasticity in two closely related elevational migrants that differ in their seasonal movements (small-scale vs. large-scale elevational migrants). Through common-garden experiments with adult male birds of these species, we compared gene and protein expression plasticity in response to changes in temperature and partial pressure of oxygen (PO₂). The small-scale elevational migrant exhibited greater plasticity in response to changes in temperature, and the large-scale elevational migrant exhibited greater plasticity in response to changes in PO₂. These findings correspond to annual variation in environmental conditions experienced by each species, suggesting that phenotypic plasticity may co-vary with the seasonal elevational distributions of these elevational migrants.