Shade seeking by Common Grackle (Quiscalus quiscula) nestlings at the scale of the nanoclimate

Solar radiation is a major source of heat for open-cup passerine nestlings, and a key variable influencing parental nest site selection. Although temperature, like food, is critical for nestling growth and survival, the use of thermal and insolation gradients when describing passerine nestling orientation and movement within the open-cup nest has not been explored. Our study used the Common Grackle (Quiscalus quiscula) as a model system to directly test the hypothesis that passerine nestlings mitigate thermal extremes behaviourally. Pairs of nestlings were tested in shaded (homogeneous) and exposed (heterogeneous) nests, movements within nests were tracked and nest temperatures recorded. Our results show that nestlings are able to detect and respond to nanoclimate heterogeneity, and can mitigate short-term radiant heat loads through shade-seeking.