02456nas a2200229   4500008004100000245010700041210006900148260001600217300001300233490000700246520173400253100001901987700001902006700002402025700001902049700002702068700002402095700002202119700001702141700001602158856005202174       2018                        eng d00aCall and be counted! Can we reliably estimate the number of callers in the indri's (Indri indri) song?0 aCall and be counted Can we reliably estimate the number of calle  cMar-08-2018  ae02016640 v133 a<p>Estimating the number of animals participating in a choral display may contribute reliable information on animal population estimates, particularly when environmental or behavioral factors restrict the possibility of visual surveys. Difficulties in providing a reliable estimate of the number of singers in a chorus are many (e.g., background noise masking, overlap). In this work, we contributed data on the vocal chorusing of the indri lemurs (Indri indri), which emit howling cries, known as songs, uttered by two to five individuals. We examined whether we could estimate the number of emitters in a chorus by screening the fundamental frequency in the spectrograms and the total duration of the songs, and the reliability of those methods when compared to the real chorus size. The spectrographic investigation appears to provide reliable information on the number of animals participating in the chorusing only when this number is limited to two or three singers. We also found that the Acoustic Complexity Index positively correlated with the real chorus size, showing that an automated analysis of the chorus may provide information about the number of singers. We can state that song duration shows a correlation with the number of emitters but also shows a remarkable variation that remains unexplained. The accuracy of the estimates can reflect the high variability in chorus size, which could be affected by group composition, season and context. In future research, a greater focus on analyzing frequency change occurring during these collective vocal displays should improve our ability to detect individuals and allow a finer tuning of the acoustic methods that may serve for monitoring chorusing mammals.</p>
1 aTorti, Valeria1 aValente, Daria1 aDe Gregorio, Chiara1 aComazzi, Carlo1 aMiaretsoa, Longondraza1 aRatsimbazafy, Jonah1 aGiacoma, Cristina1 aGamba, Marco1 aReby, David  uhttp://dx.plos.org/10.1371/journal.pone.0201664