frequency range and the power wanes in higher frequencies, as in many tiger vocalizations, yet a distinct pattern allows prusten to be distinguished. It has been found that tigers are most sensitive to lower frequencies and are likely able to hear in the infrasonic range, which is likely reflected in the production of calls such as prusten. It has also been hypothesized that hearing in the low frequency range is beneficial in communicating and locating prey in the low-visibility jungle habitats where these cats usually live. Purpose Prusten is social in nature, and may be produced for a variety of purposes. In captive tigers, it is more likely to be expressed when the animals are housed in groups rather than individually. Cats may produce the vocalization both to each other in greeting, or to familiar people such as zookeepers, as seen in clouded leopards. It is used to signal friendly intent to the other animal, and is generally reciprocated by other felids. It may also signify happiness, as content leopards tend to be more vocal and produce prusten more frequently. In the clouded leopard and tiger, it has been observed that females often express this vocalization during estrous. This has also been noted in snow leopards, and is on occasion used by females to initiate mating with a male. It is frequently used by felid mothers when returning to her den in greeting to her cubs, and the cubs begin to produce this vocalization at around 5 weeks in snow leopards. Significance This vocalization is distinct from friendly and non-threatening vocalizations produced by other felids, and thus has been described as a behavioural apomorphy. This distinction has been useful in determining evolutionary relationships between members of the family Felidae. Prusten may be able to serve as an indication of well-being. It is also valuable for conservation purposes, along with other unique felid vocalizations, and may enable the location and monitoring of both individuals and populations in their habitats. Ongoing studies seek to determine if there are individual differences in the acoustic pattern of tiger vocalizations that would aid in monitoring and conservation practices. This hypothesis is the basis of The Prusten Project, which analyses individual tiger calls with the goal of developing and implementing non-invasive monitoring systems as a conservation tool. See also Purr References External links http://www.lairweb.org.nz/tiger/Tiger3a.wav Animal sounds