Erratum to: Born to sing! Song development in a singing primate

The pagination of this article online has been updated to pages 597-608 to match the print version.The Publisher sincerely apologizes for introducing this error online.

Evidence for acoustic discrimination in lemurs: A playback study on wild indris Indri indri

Indris Indri indri are group-living lemurs that occupy stable territories over several years and perform remarkable long-distance vocal displays.Vocal exchanges between long-term territory neighbors may contribute to assessing reciprocal resource-holding potentials, thus adaptivelyreducing the costs of territorial defense by limiting aggressive escalation. Previous work showed that indris’ songs show distinctive acousticfeatures at individual and group level. However, the possibility that indris use such cues for individual or group-level recognition has never beeninvestigated experimentally. We conducted a playback experiment to test whether indris discriminate between familiar and nonfamiliar songs.Our rationale lies in the hypothesis of the dear enemy phenomenon, which predicts that territorial animals will show reduced aggression levelstoward familiar neighbors compared with novel rivals. We played back stimulus recordings to wild indris from their territory boundaries andexamined their responses in terms of vocal and behavioral indicators of willingness to engage in a fight. In line with our predictions, focal animals responded more rapidly and approached more often the speaker in response to playback stimuli of nonfamiliar individuals than to stimuliof neighboring groups. These results indicate that indris can discriminate between different classes of intruders based on distinctive acousticfeatures of their song choruses. We suggest that increased aggression directed toward unfamiliar intruders may be explained by higher threatlevels associated with dispersal and group formation dynamics. We further discuss the relevance of these findings in a strepsirrhine primatemodel for comparative studies of vocal communication and sociality.

Female indris determine the rhythmic structure of the song and sustain a higher cost when the chorus size increases

Among the behavioral traits shared by some nonhuman primate species and humans there is singing. Unfortunately, our understanding of animals' rhythmic abilities is still in its infancy. Indris are the only lemurs who sing and live in monogamous pairs, usually forming a group with their offspri ng. All adult members of a group usually participate in choruses that are emitted regularly and play a role in advertising territorial occupa ncy and in tergroup spaci ng. Males and females emit phrases that have similar frequency ranges but may differ in their temporal structure. We examined whether the individuals' contribution to the song may change according to chorus size, the total duration of the song or the duration of the individual con tribution using the in ter-on set intervals within a phrase and between phrases. We found that the rhythmic structure of indri's songs depends on factors that are different for males and females. We showed that females have sigrdficantly higher variation in the rhythm of their contribution to the song and that, changes according to chorus size. Our findings indicate that female indris sustain a higher cost of singing than males whe n the nu mber of singers in creases. These results suggest that cross-species investigatio ns will be crucial to un derstanding the evoluti on ary frame in which such sexually dimorphic traits occurred.

Born to sing!Song development in a singing primate

In animal vocal communication,the development of adult-like vocalization is fundamental to interact appropriately with conspecifics.However,the factors that guide ontogenetic changes in the acoustic features remain poorly understood.In contrast with a historical view of nonhuman primate vocal production as substantially innate,recent research suggests that inheritance and physiological modification can only explain some of the developmental changes in call structure during growth.A particular case of acoustic communication is the indris’singing behavior,a peculiar case among Strepsirrhine primates.Thanks to a decade of intense data collection,this work provides the first long-term quantitative analysis on song development in a singing primate.To understand the ontogeny of such a complex vocal output,we investigated juvenile and sub-adult indris’vocal behavior,and we found that young individuals started participating in the chorus years earlier than previously reported.Our results indicated that spectro-temporal song parameters underwent essential changes during growth.In particular,the age and sex of the emitter influenced the indris’vocal activity.We found that frequency parameters showed consistent changes across the sexes,but the temporal features showed different developmental trajectories for males and females.Given the low level of morphological sexual dimorphism and the marked differences in vocal behavior,we hypothesize that factors like social influences and auditory feedback may affect songs’features,resulting in high vocal flexibility in juvenile indris.This trait may be pivotal in a species that engages in choruses with rapid vocal turn-taking.