The true cost of migration: testing the species-energy hypothesis by quantifying the energy budget of free flying avian migrants under spatially explicit environmental conditions

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Migration is a key life-history stage for many avian species and underpins the distribution of biodiversity on Earth. The species-energy hypothesis states that energetics underlies spatial- and temporally-specific patterns; yet the energetic balance for free-flying migratory species is poorly understood due to the inherent difficulties in studying individuals across vast geographic scales. To date, it has not been possible to obtain a field-derived metric of energetics in passerines let alone relate it to the environmental energetic conditions experienced. Major advances at the MPI-AB in the miniaturisation of heart-rate loggers, and the launch of ICARUS tracking technology with high spatio-temporal resolution, will now enable unique insights into energetically costly flight behaviour over the full annual cycle. By filling a technological and a conceptual gap, the ER will be the first to develop a novel, integrated approach to quantify the true energetic costs in the natural environment across a continuum of flight strategies, and calibrate metabolic costs under controlled settings to transform the research field of energetics. Empirically-derived data, resulting from this action, will be used to test if the species-energy relationship is applicable to the vast majority of small songbirds which change their distribution in response to seasonal variation in conditions and resources. Furthermore, this will enable the development of a tool to refine flight performance models and determine the response of this biological system to climate change. It will permit explicit testing of the species-energy relationship under seasonally specific environmental conditions, with a unique approach of incorporating energetic demands into the system. Cumulatively, fulfilling the objectives of TesSSEH, will significantly contribute to biogeographic theory, develop our understanding of energetically efficient physiological traits and revolutionise avian energetic models.