A cuckoo clock is a clock, typically a pendulum clock, that strikes the hours using small bellows and whistles that imitate the call of the Common Cuckoo bird in addition to striking on a wire gong.
The design of a cuckoo clock is now conventional. Most are made in the shape of a rustic birdhouse or chalet. They hang on the wall, and are housed in wooden cases, frequently decorated with carved leaves; sometimes deer and other animals are added. Most now have an automaton of the bird that appears through a small trap door when the clock is striking, and vanishes behind the door after the clock is done.
The bird is often made to move while the clock strikes, typically by means of an arm that lifts the back of the carving. Some have musical movements, and play a tune on a music box after striking the hours or half-hours. Musical cuckoo clocks frequently have other automata that move when the music box plays. The clocks are almost always weight driven; a very few cuckoo clocks are spring driven.
In recent years, fake quartz battery powered cuckoo clocks have been sold; these do not have genuine cuckoo bellows, and typically generate their striking sounds electronically. The weights are conventionally cast in the shape of pine cones. The pendulum bob is often another carved leaf. The dial is small, and typically marked with Roman numerals.
In spite of being a widely known product, the origin of the cuckoo clock has never been clarified, that is where, when and who invented it. The first Black Forest cuckoo clocks were made between 1740 and 1750, not in 1730 as is so often cited in horological literature. There are two main fables from the XVIII and XIX centuries which tell conflicting stories about the origin of the cuckoo clock: The first is from Father Franz Steyrer, written in 1796. He describes a meeting between two clock traders from Furtwangen (Black Forest) who while travelling met a Bohemian trader who sold wooden cuckoo clocks. Both of the Furtwangen traders were so excited at seeing this that they bought one. On bringing it home they imitated it and showed their imitation to other Black Forest clock traders. Popularity grew for the cuckoo clock in the region and more and more clock traders began producing them. The second one is related by another priest, Markus Fidelis Jäck, in a passage from his report "Darstellungen aus der Industrie und des Verkehrs aus dem Schwarzwald" ("Description of Industry and Commerce of the Black Forest"), 1810; "The cuckoo clock was invented by a clock-master from Schönwald (Black Forest). This craftsman adorned a clock with a moving bird that announced the hour with the cuckoo-call. The clock-master got the idea of how to make the cuckoo-call from the bellows of a church organ". As time went on, the second version became the more popular, and is generally the one related today.
R. Dorer had pointed out, in 1948, that Franz Anton Ketterer could not have been the inventor of the cuckoo clock in 1730 because of he was not born yet. Gerd Bender in "Die Uhrenmacher des hohen Schwarzwaldes und ihre Werke" wrote that the cuckoo clock was not native to the Black Forest. Schaaf in "Schwarzwalduhren", provides his own research which leads to the earliest cuckoos being in the "Franken-Niederbayern" (Germany) area, in the direction of Bohemia (Czeck Republic), which he notes, lends credence to the Steyrer version.
Although probably the idea of placing a cuckoo bird in a clock was not originated in the Black Forest, it is necessary to emphasize that the cuckoo clock as we know it today, comes from this region located in the southwest of Germany whose tradition of clockmaking started back in the XVII century. Indeed were the people and artisans from the Black Forest who created the cuckoo clock industry, developed it and they still keep innovating with new designs, working out others and using technical improvements which have made the cuckoo clock a valued work of art all over the world.
(quote: http://en.wikipedia.org)