Combinatoriality in the vocal systems of nonhuman animals

1) Humpback whales (Megaptera novaeangliae) produce a series of beautiful and varied sounds for a period of 7 to 30 minutes and then repeat the same series with considerable precision. We call such a performance "singing" and each repeated series of sounds a "song." 2) All prolonged sound patterns (recorded so far) of this species are in song form, and each individual adheres to its own song type. 3) There seem to be several song types around which whales construct their songs, but individual variations are pronounced (there is only a very rough species-specific song pattern). 4) Songs are repeated without any obvious pause between them; thus song sessions may continue for several hours. 5) The sequence of themes in successive songs by the same individual is the same. Although the number of phrases per theme varies, no theme is ever completely omitted in our sample. 6) Loud sounds in the ocean, for example dynamite blasts, do not seem to affect the whale's songs. 7) The sex of the performer of any of the songs we have studied is unknown. 8) The function of the songs is unknown.

Many animals produce alarm signals when they detect a potential predator, but we still know little about the information contained in these signals. Using presentations of 15 species of live predators, we show that acoustic features of the mobbing calls of black-capped chickadees (Poecile atricapilla) vary with the size of the predator. Companion playback experiments revealed that chickadees detect this information and that the intensity of mobbing behavior is related to the size and threat of the potential predator. This study demonstrates an unsuspected level of complexity and sophistication in avian alarm calls.