A cuckoo clock is a clock, typically pendulum-driven, that strikes the hours using small bellows and pipes that imitate the call of the Common Cuckoo in addition to striking a wire gong. The mechanism to produce the cuckoo call was installed in almost every kind of cuckoo clock since the middle of the eighteenth century and has remained almost without variation until the present.

The design of a cuckoo clock is now conventional. Most are made in the "traditional style" (also known as "carved") or "chalet" to hang on a wall. In the "traditional style" the wooden case is decorated with carved leaves and animals. Most now have an automaton of the bird that appears through a small trap door while the clock is striking. The bird is often made to move while the clock strikes, typically by means of an arm that lifts the back of the carving.

There are two kinds of movements: one-day (30-hour) and eight-day movements. Some have musical movements, and play a tune on a Swiss music box after striking the hours and half-hours. Usually the melody sounds only at full hours in eight-day clocks and both at full and half hours in one-day clocks. Musical cuckoo clocks frequently have other automata which move when the music box plays. Today's cuckoo clocks are almost always weight driven, though a very few are spring driven. The weights are made of cast iron in a pine cone shape and the "cuc-koo" sound is created by two tiny gedackt (pipes) in the clock, with bellows attached to their tops. The clock's movement activates the bellows to send a puff of air into each pipe alternately when the clock strikes.

In recent years, quartz battery-powered cuckoo clocks have been available. As on mechanical cuckoo clocks, the cuckoo bird emerges from its enclosure and moves up and down, on some quartz clocks it also flaps its wings as it calls, but instead of the call being reproduced by the traditional bellows, the call is a digital recording of a cuckoo calling in the wild (with a corresponding echo). The cuckoo call is usually accompanied by the sound of a water fall and other bird call in the background. During the cuckoo call the double doors open and the cuckoo emerges as usual, but only at the full hour, and they do not have a gong wire.
In musical quartz clocks, the hourly chime is followed by the replay of one of twelve popular melodies (one for each hour). Some musical quartz clocks also reproduce many of the popular automata found on mechanical musical clocks, such as beer drinkers, wood choppers, jumping deer, and angry wives beating lazy husbands. One thing that is unique about the quartz cuckoo clocks is that they include a light sensor, so that when the lights are turned off at night, they automatically silence the hourly chime. The weights are conventionally cast in the shape of pine cones made of plastic, as well as the cuckoo bird and hands. The pendulum bob is often another carved leaf. The weights and pendulum are purely ornamental though, as the clock is driven by battery power. As with mechanical cuckoo clocks, the dial is usually small, and typically marked with Roman numerals.
 

Since antiquity there have been timepieces with an automaton bird. The first one is credited to the Greek mathematician, Ctesibius of Alexandria (ca.285-222 BC), who in the second century B. C. "used water to sound a whistle and make a model owl move. He had invented the world's first "cuckoo" clock".[1] Ctesibius may indeed lay claim to the first known "singing" clock which could be considered the ancestor of the modern cuckoo clocks.

Later, in the Middle Ages, in 797 (or possibly 801), the caliph of Baghdad, Harun al-Rashid, presented Charlemagne with an Asian elephant named Abul-Abbas and a mechanical clock, out of which came a mechanical bird to announce the hours.[3] The maker of this clock remains unknown.

On the other hand, the elephant clock, invented by the Arab inventor Al-Jazari, featured a humanoid automaton in the form of a mahout striking a cymbal and a mechanical bird chirping after every hour or half-hour.
Finally, in Europe during the Late Middle Ages and later, roosters were used to call the hours in some clocks, like the first astronomical clock in Strasbourg Cathedral.
 

The first modern cuckoo clocks

Mechanical cuckoo, 1650
In 1629, many decades before clockmaking was established in the Black Forest,[4] an Augsburg nobleman by the name of Philipp Hainhofer (1578–1647) penned the first known description of a modern cuckoo clock.[5] The clock belonged to Prince Elector August von Sachsen.
In a widely known handbook on music, Musurgia Universalis (1650), the scholar Athanasius Kircher describes a mechanical organ with several automated figures, including a mechanical cuckoo. This book contains the first documented description -in words and pictures- of how a mechanical cuckoo works.[6] We must assume that Kircher did not invent the cuckoo mechanism, because this book, like his other works, is a compilation of known facts into a handbook for reference purposes. The engraving clearly shows all the elements of a mechanical cuckoo. The bird automatically opens its beak and moves both its wings and tail. Simultaneously, we hear the whistle - call of the cuckoo, created by two whistles of organ pipes, tuned to a minor or major third. There is only one fundamental difference from the Black Forest-type cuckoo mechanism: The functions of Kircher's bird are not governed by a count wheel in a strike train, but a pinned program barrel synchronizes the movements and sounds of the bird.
In 1669 Domenico Martinelli, in his handbook on elementary clocks "Horologi Elementari", suggests using the call of the cuckoo to indicate the hours.[7] Starting at that time the mechanism of the cuckoo clock was known. Any mechanic or clockmaker, who could read Latin or Italian, knew after reading the books that it was feasible to have the cuckoo announce the hours.

Subsequently, cuckoo clocks appeared in regions that had not been known for their clockmaking. For instance, the Historische Nachrichten (1713), an anonymous publication generally attributed to Court Preacher Bartholomäus Holzfuss, mentions a musical clock in the Oranienburg palace in Berlin. This clock, originating in West Prussia, played eight church hymns and had a cuckoo that announced the quarter hours.[8] Unfortunately this clock, like the one mentioned by Hainhofer in 1629, can no longer be traced today.

A few decades later, people in the Black Forest started to build cuckoo clocks.

The first cuckoo clocks made in the Black Forest

It is not clear who built the first cuckoo clocks in the Black Forest[10] but there is unanimity that the unusual clock with the bird call very quickly conquered the region. Already by the middle of the eighteenth century, several small clockmaking shops produced cuckoo clocks with wooden gears. So the first Black Forest cuckoo clocks were created between 1740 and 1750. They had hand-painted shields.
It is hard to judge how large the proportion of cuckoo clocks was among the total production of modern movement Black Forest clocks. Based on the proportions of pieces surviving to the present, it must have been a small fraction of the total production.

About its murky origins, there are two main fables from the first two chroniclers of Black Forest horology which tell contradicting stories about the origin of the cuckoo clock:
The first is from Father Franz Steyrer, written in his "Geschichte der Schwarzwälder Uhrmacherkunst" (History of Clockmaking in the Black Forest) in 1796. He describes a meeting between two clock peddlers from Furtwangen (a town in the Black Forest) who met a travelling Bohemian merchant who sold wooden cuckoo clocks. Both the Furtwangen traders were so excited that they bought one. On bringing it home they copied it and showed their imitation to other Black Forest clock traders. Its popularity grew in the region and more and more clockmakers started producing them. With regard to this chronicle, the historian Adolf Kistner claimed in his book "Die Schwarzwälder Uhr" (The Black Forest Clock) published in 1927, that there is not any Bohemian cuckoo clock in existence to verify the thesis that this clock was used as a sample to copy and produce Black Forest cuckoo clocks. Bohemia had no fundamental clockmaking industry during this period.

The second story 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 (in 1730) by a clock-master (Franz Anton Ketterer) 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 the one generally related today. Unfortunately, neither Steyrer nor Jäck quote any sources for their claims, making them unverifiable.

Early cuckoo clock, Black Forest, 1760-1780 (Deutsches Uhrenmuseum, Inv. 03-2002)
On the other hand R. Dorer pointed out, in 1948, that Franz Anton Ketterer (1734–1806) could not have been the inventor of the cuckoo clock in 1730 because he hadn't then been born. Gerd Bender in the most recent edition of the first volume of his work "Die Uhrenmacher des hohen Schwarzwaldes und ihre Werke" (The Clockmakers of the High Black Forest and their Works) (1998) wrote that the cuckoo clock was not native to the Black Forest and also stated that: "There are no traces of the first production line of cuckoo clocks made by Ketterer". Schaaf in "Schwarzwalduhren" (Black Forest Clocks) (1995), provides his own research which leads to the earliest cuckoos being in the "Franken-Niederbayern" area (East of Germany), in the direction of Bohemia (a region of the Czech Republic), which he notes, lends credence to the Steyrer version.

The legend that the cuckoo clock was invented by a clever Black Forest mechanic in 1730 (Franz Anton Ketterer) keeps being told over and over again. But all of this is not true.[12] The cuckoo clock is much older than clockmaking in the Black Forest. As early as 1650 the bird with the distinctive call was part of the reference book knowledge recorded in handbooks. It took nearly a century for the cuckoo clock to find its way to the Black Forest, where for many decades it remained a tiny niche product.

Although the idea of placing a cuckoo bird in a clock did not originate in the Black Forest, it is necessary to emphasize that the cuckoo clock as we know it today, comes from this region located in southwest Germany whose tradition of clockmaking started in the late seventeenth century. The Black Forest people who created the cuckoo clock industry developed it, and still come up with new designs and technical improvements which have made the cuckoo clock a valued work of art all over the world. The cuckoo clock history is linked to the Black Forest.

Even though the functionality of the cuckoo mechanism has remained basically unchanged, the appearance has changed as case designs and clock movements evolved in the region. In the beginning of the 19th century the now traditional Black Forest clock design, the "Schilduhr" (Shield-clock), was characterized by having a painted flat square wooden face behind which all the clockwork was attached. On top of the square was usually a semicircle of highly decorated painted wood which contained the door for the cuckoo. These usually depicted floral patterns (so-called “Rosenuhren”) and often had a painted column, on either side of the chapter ring, others were decorated with illustrations of fruit as well. Some clocks also bore the names of the bride and bridegroom on the dial, which were normally painted by women.[13] There was no cabinet surrounding the clockwork in this model. This design was the most prevalent between the end of the eighteenth century and the first half of the nineteenth century. These clocks were typically sold from door to door by "Uhrenträger" (Clock-peddlers) who would carry the dials and movements on their backs displayed on huge backpacks.

About the middle of the nineteenth century till the 1870s, cuckoo clocks were also manufactured in the Black Forest type of clock known as "Rahmenuhr" (Framed-clock). As the name suggests, these scarce cuckoo clocks consisted of a picture frame, usually with a typical Black Forest scene painted on a wooden background or a sheet metal, lithography and screen-printing were other techniques used. Other common themes depicted were; hunting, love, family, death, birth, mythology, military and Christian religious scenes. Works by painters such as Johann Baptist Laule (1817–1895) and Carl Heine (1842–1882) were used to decorate the fronts of this and other types of clocks. The painting was almost always protected by a glass and some models displayed a person or an animal with blinking or flirty eyes as well, being operated by a simple mechanism worked by means of the pendulum swinging. Most of them were wall clocks but a few were mantel clocks. The cuckoo normally took part in the scene painted, and would pop out in 3D, as usual, to announce the hour.

From the 1860s until the twenties, and according to the decorative tastes prevailing in each moment, cuckoo clock cases were manufactured following different styles then in vogue such as; Biedermier (some models also included a painting of a person or animal with moving eyes), Neoclassical, Gothic, Renaissance, Baroque, Art Nouveau, etc. These timepieces, based both on architectural and home decorative styles, are rarer than the popular ones looking like gatekeeper-houses (Bahnhäusle style clocks) and they could be mantel, wall or bracket clocks.
But the popular house-shaped Bahnhäusleuhr (Railroad house clock) virtually forced the discontinuation of other designs within a few years.