Outside source

This is the famous European bird whose voice is imitated by cuckoo clocks (and whose call, coo-coo, gave the name to the entire cuckoo family).
The cuckoo makes its presence known to our little protagonists as they look to it for guidance.

"Though many natives of the Black Forest like to believe that the cuckoo clock was invented by a brilliant local, evidence suggests that cuckoo clocks, albeit in a form different from its modern avatar, existed elsewhere in the country long before they found their way to the Black Forest. However, the credit for innovating the cuckoo clock to the stylized work of art as it is today does, indeed, go to the Black Forest.

Nobody knows for certain how cuckoo clocks came to be produced in the Black Forest or exactly when. Some theories suggest that by the late 17th century, farmers in the region had learned to make cuckoo clocks out of wood collected from the forest in order to supplement their earnings in colder months. While this can’t be proven, there is enough evidence to suggest that by the mid-18th century, several clock-makers in the Black Forest were adept in hand-carving wooden cuckoo clocks. However, cuckoo clock production remained a small and niche segment for the next couple of centuries."
-theculturetrip.com

LINK Sound of the Cuckoo