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Weather
American kestrels are often useful in scientific studies on animal physiology, and are typically captured using the bal-chatri method or raised in nest boxes Kestrel metabolic rate increases in response to rainfall, and at ambient temperatures below about 25⁰C. Metabolic responses to weather and temperature do not vary, however, with sex Kestrels will increase their oxygen consumption, and therefore their metabolic rate in cold and wet conditions to counteract heat loss.

Environmental Disturbance
American kestrels' response to environmental stress is measured as blood concentration of corticosterone (CORT,) a hormone produced by the hypothalamic-pituitary-adrenal (HPA) axis that releases stored energy for essential body functions. Extended periods of elevated blood CORT levels may direct metabolic energy away from growth and reproduction. Thus, high levels of traffic disturbance and human development surrounding American kestrel nests are found to increase stress hormones leading to reproductive failure. Among successful nests, however, nestlings do not typically experience a higher stress response to environmental human disturbance, suggesting that they can tolerate a degree of human activity near the nest.

Environmental Contaminants
Since American kestrels are carnivores, toxic chemical runoff ingested by their prey can concentrate at high levels in their blood. Wild kestrels are subject to immunomodulation, or an altered immune response, to polybrominated diphenyl ethers (PBDEs), a group of industrial flame retardants that may leach from factories into the environment. When PBDEs accumulate in body tissues of kestrels, the T-cell mediated immune response decreases in efficiency.