falcon, eagle
鶻 centers on a specific bird of prey: a falcon or eagle. The two given meanings are closely related, both referring to large, powerful hunting birds.
鶻 combines 骨 (bone) and 鳥 (bird). The exact historical reason for the bone component is uncertain; it may have originally contributed a phonetic element or been used to describe a bony or strong bird of prey.
A bird (鳥) with prominent bones (骨) suggests a lean, powerful hunter: a falcon or eagle.
For コツ, imagine a falcon's sharp beak tapping against bone with a hard 'kots' sound: kots -> コツ.