wild animals, including the Western scarecrow). Instead of using a visual method to distract pests, as the scarecrow does, it uses the sound of a heavy pipe repeatedly and rhythmically hitting a rock, using water as a timing device. The sōzu is also used in Japanese popular culture to denote inordinate amounts of wealth, combined with a traditional sensibility: by design, the shishi odoshi uses copious amounts of water, meaning either a very high water bill, or that it is situated on high-value land with a stream or river running through it. Propane cannons Propane scare cannons are one of the most common types of bird scarer available in Europe and America. It is a propane-powered gas gun which produces a periodic explosion. The audible bang can reach very loud volumes, in excess of 150 decibels, causing a flight reaction in birds. The similarity between a scare cannon and a 12 gauge shotgun is thought to cause a startle/fear reaction, although it is also effective against birds that have not been exposed to hunting pressure. Birds can become habituated to the sound of regular cannon detonations, especially if it does not vary in its magnitude, pitch, or time interval. However, regularly moving the cannon, utilizing on-demand firing options, including radio control, and combining cannons with other methods of deterrents can prevent habituation. Propane scare cannons are very loud and can be disruptive to people living nearby. One study found that restricting cannon use to only hours when birds are active and incorporating better bird damage plans drastically reduced the number of complaints from neighbours. Electronic repellers Sonic bird repellers are not effective; the birds quickly acclimate to them. Usually consisting of a central unit and several speakers, the system emits digitally recorded distress calls of birds, and, in some cases, calls of predators of the target species. Some emitters randomize pitch, magnitude, time interval, sound sequence and other factors in an attempt to prevent birds from getting used to them. Many of the sounds produced are regarded as annoying to people. Ultrasonic scarers Ultrasonic devices are static sound-emitting bird deterrents, which, in theory, will annoy birds to keep them away from enclosed or semi-enclosed areas. Ultrasonic scarers are not harmful to birds, however, there is debate around birds' ability to hear these frequencies at loud enough decibels. Birds are believed to have similar hearing to humans, with studies showing birds