Potential for bird-insect phenological mismatch in a tri-trophic system

Climate change is altering the seasonal timing of biological events across the tree of life. Phenological asynchrony has the potential to hasten population declines and disrupt ecosystem function. However, we lack broad comparisons of the degree of sensitivity to common phenological cues across multiple trophic levels. Overcoming the complexity of integrating data across trophic levels is essential for identifying spatial locations and species for which mismatches are most likely to occur. Here, we synthesized over 15 years of data across three trophic levels to estimate the timing of four interacting phenological events in eastern North America: the green-up of forest canopy trees, emergence of adult Lepidoptera and arrival and subsequent breeding of migratory birds. We next quantified the magnitude of phenological shift per one unit change of springtime temperature accumulation as measured by accumulated growing degree days (GDD). We expected trophic responses to spring temperature accumulation to be related to physiology, thus predicting a weaker response of birds to GDD than that of insects and plants. We found that insect and plant phenology indeed had similarly strong sensitivity to GDD, while bird phenology had lower sensitivity. We also found that vegetation green-up and bird arrival were more sensitive to GDD in higher latitudes, but the timing of bird breeding was less sensitive to GDD in higher latitudes. Migratory bird species with slow migration pace, early arrivals and more northerly wintering grounds shifted their arrival the most. Across Eastern Temperate Forests, the similar responses of vegetation green-up and Lepidoptera emergence to temperature shifts support the use of remotely sensed green-up to track how the timing of bird food resources is shifting in response to climate change. Our results indicate that, across our plant-insect-bird system, the bird-insect phenological link has a greater potential for phenological mismatch than the insect-plant link, with a higher risk of decoupling at higher latitudes.