The function of male and female long-distance vocalizations in three mammalian taxa
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Recent research has demonstrated that female birdsong is present in the majority of songbird species worldwide. In addition, the results indicated that female birdsong was already present in the common ancestor of modern songbirds. These results are rather unexpected as it was generally believed that birdsong has evolved especially in male songbirds by ways of sexual selection. Similarly to research on birdsong, research on long-distance vocalizations in mammals often focuses on males. However, within many mammalian species these vocalizations are used by females as well. This study provides an overview of the production of long-distance vocalizations by males and females in three mammalian taxa: simian primates (Simiiformes), ungulates (Perissodactyla and Cetartiodactyla) and bats (Chiroptera). Additionally, an attempt was made to determine the function of these long-distance vocalizations. Five functional hypotheses of long-distance vocalizations have been proposed: 1) defence hypothesis; 2) alarm hypothesis; 3) spatial coherence hypothesis; 4) intragroup competition hypothesis and 5) finding a mate hypothesis. Data on long-distance vocalizations in the three mammalian taxa were gathered from literature. Factors indicative for a call’s function, like call stimulus, consequence, and characteristics of the signaller, were included in the data acquisition. The results reveal that long-distance vocalizations were present in 63 species of simians, 26 species of ungulates and eight species of bats. These vocalizations were most often produced by individuals of both sexes within a species or exclusively by males. Females rarely produced long-distance vocalizations when males within the same species did not. All proposed functions were found in at least one of the researched taxa. The fact that long-distance vocalizations are present in both males and females and that these vocalizations serve distinct functions, suggests that long-distance vocalizations have evolved under different environmental and social conditions. Above all, similarly to birdsong, long-distance calls may have been present in ancestral primates, ungulates and bats.