Which species is most sensitive to weight fluctuations?

The American Kestrel is recognized as the species most sensitive to weight fluctuations due to its smaller size and high metabolic rate. Falcons, like the Gyrfalcon and Peregrine Falcon, and larger hawks such as the Red-tailed Hawk experience weight changes, but they have a greater body mass that can buffer against the effects of minor weight loss or gain. Kestrels, being much smaller, require more frequent feeding to maintain their energy levels and overall health, making them more vulnerable to the impacts of even slight variations in body weight. Thus, maintaining an optimal weight for American Kestrels is crucial for their performance and wellbeing in falconry.