Merlins can be distinguished from American Kestrels by their:

Merlins can be distinguished from American Kestrels by their broader and stockier build. This physical characteristic sets Merlins apart, as they tend to have a more robust, compact body compared to the more slender and delicate structure of kestrels.

Merlins are known for their strong, muscular build, which enables them to be powerful hunters. This broader build, coupled with their shorter tails relative to their body size, differentiates them from American Kestrels, which have a more elongated and slender appearance. Understanding this distinction is important for ornithologists and falconers, as it assists in the identification of these two species in the field, particularly when observing their behaviors or habitats.

In contrast, size comparison is less definitive, as both species can vary in size. The other options regarding wing shape and tail size are also not reliable indicators for distinguishing between these two species, as both birds exhibit wings and tails that suit their hunting styles without making one markedly different from the other in those aspects.