Valeria Torti

Behavioral correlates of extra-pair copulation in Indri indri

Active pursuit of extra-pair mating has been reported for Indri indri, the socially monogamous largest living lemur. This study, conducted in a mountain rainforest in eastern Madagascar, presents the first evidence for extra-pair mating of indri and discusses the alternative mating strategy and alteration of the social, territorial, spatial, and vocal behavior of the adult female of a group of wild indris. Further studies may investigate whether extra-pair copulation is an attempt to breed with a partner of superior quality and thus lead to extra-pair paternity. If so, it could potentially play a role in maintaining genetic variability within a population.

The songs of the indris (Mammalia: Primates: Indridae): contextual variation in the long-distance calls of a lemur

Abstract Contextual variation in the loud calls of strepsirhine primates is poorly understood. To understand whether songs given by indris in different contexts represent acoustically distinct variants and have the potential to elicit context-specific behaviours in conspecific listeners, we investigated the acoustic variability of these songs and the distance travelled by vocalizers after their emissions. Songs of 41 individuals were recorded from 16 indri groups in four different forest sites in eastern Madagascar. We collected a total of 270 duets and choruses arising during territorial defence, advertisement and cohesion. We demonstrated that the structure of indri songs conveyed context-specific information through their overall duration, but shared the sequential pattern of harsh units (roars) followed by long notes and, finally, descending phrases. Analysing in detail individual contributions to advertisement songs and cohesion songs, we found that the acoustic structure of units could be classified correctly with a high degree of reliability (96.23% of long notes, 80.16% of the descending phrases, 72.54% of roars). Future investigations using playback stimuli could explore the relationship between acoustic features and the information transmitted by the song.

Comparative Analysis of the Vocal Repertoire of Eulemur : A Dynamic Time Warping Approach

The diversity of qualitative approaches and analytical methods has often undermined comparative research on primate vocal repertoires. The purpose of the present work is to introduce a quantitative method based on dynamic time warping to the study of repertoire size in Eulemur spp. We obtained a large sample of calls of E. coronatus, E. flavifrons, E. fulvus, E. macaco, E. mongoz, E. rubriventer, and E. rufus, recorded between 1999 and 2013 from captive and wild lemurs. We inspected recordings visually using spectrograms, then cut and saved high-quality vocal emissions to single files for further analysis. We extracted the acoustic features of all vocalizations of a species using the Hidden Markov Model Toolkit, an application of dynamic time warping, and then compared cepstral coefficients (a feature widely used in automatic speaker recognition) pairwise. We analyzed the results using affinity propagation clustering. We found that Eulemur species share most of their vocal repertoire but species-specific calls determine repertoire size differences. Repertoire size varied from 9 to 14 vocalization types among species, with a mean of 11.

Overlapping And Synchronization In The Song Of The Indris (Indri indri)

The interplay between synchronous and asynchronous displays in communicative interactions are based over sequential symmetry formations and symmetry breaks, which may involve postural, gestural, and vocal displays (Rotondo & Boker, 2002; Adger-Antonikowski, 2008). Thus, it has been hypothesized that the spatio-temporal structure of the formation and breaking of symmetry can be diagnostic of social and cognitive aspects of human dyadic In Indri indri, males and females within a social group emit loud, long distance calls in a coordinated manner. An indri may start emitting a vocal utterance before the end of another individual’s contribution, resulting in different degrees of overlap between individual songs. This study provides the first quantitative analysis of the individual overlap between indri males and females showing the adult pair members mainly overlap each other. The adult female song also has an effect on male singing in 35% of the cases, while the timing of a song unit could predict the occurrence of a unit sung by another group-member in only 10% of the other dyads (e.g. male-female or male-youngster). PUBLISHED AS / CITE THIS AS:

Territory exclusivity and intergroup encounters in the indris (Mammalia: Primates: Indridae: Indri indri) upon methodological tuning

Abstract Territorial, socially monogamous species actively defend their home range against conspecifics to maintain exclusive access to resources such as food or mates. Primates use scent marks and loud calls to signal territory occupancy and limit the risk of intergroup encounters, maximizing their energetic balance. Indri indri is a little-studied territorial, socially monogamous singing primate living in family groups. The groups announce territory occupancy with long-distance calls, and actively defend their territories from conspecific intruders. This work includes data collected in three forests in Madagascar on 16 indri groups over up to 5 years. We aimed (1) to estimate the extent of territories using minimum convex polygon (MCP), implementing minimum sampling effort requirements; (2) to quantify territorial exclusivity, measuring the overlap between territories; and (3) to evaluate the intergroup encounter rate and to quantify the dynamics of group encounters. Our results showed that indris range evenly within exclusive small territories with no or little overlap. Intergroup encounters are rare (0.05 encounters per day), and are located on the periphery of the territories. Disputes were mostly solved with vocal confrontation and only in 13% of the cases ended in physical fights. This frame underlines a cost–benefit explanation of territoriality, favouring a strategy that efficiently limits overlap and avoids costly intergroup encounters. We hypothesize that territorial behaviour in indri is related to mate-guarding strategy and that vocal behaviour plays a fundamental role in regulating intergroup spacing dynamics.

Primate songs and their relevance in the study of language evolution

It has been suggested that early human vocal communication should result from at least two critical abilities: the ability to engage in cooperative efforts (Levinson, 2005), and the ability to combine sounds in larger structures (Collier et al., 2014). These characteristics are essential features of choral songs, and, in fact, Darwin speculated that language might have originated from singing. The rhythms and pitch contours that distinguish songs in other species may be investigated to understand the roots of our language. Many authors have indicated birds and singing primates as the natural target of these studies (Geissmann, 2000). The evolution of songs in nonhuman primates has been associated with a monogamous mating system and to the active defense of a territory. We have investigated the layers of complexity of the songs emitted by three nonhuman primate species: the siamang (Symphalangus syndactylus), the white-handed gibbon (Hylobates lar), and the indri (Indri indri). Although the single species have received attention from scientists, a comparative approach investigating frequency variation and individual temporal patterns has never been used. For each of these species, we analyzed songs from different social groups and hierarchically classified the units emitted in the songs in phrases using dynamic time warping and cluster analysis. For each unit, we extracted a pitch 134

Call and be counted! Can we reliably estimate the number of callers in the indri's (Indri indri) song?

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.

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

Abstract 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 offspring. All adult members of a group usually participate in choruses that are emitted regularly and play a role in advertising territorial occupancy and intergroup spacing. 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 contribution using the inter-onset 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 significantly 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 when the number of singers increases. These results suggest that cross-species investigations will be crucial to understanding the evolutionary frame in which such sexually dimorphic traits occurred.

An intra-population analysis of the indris’ song dissimilarity in the light of genetic distance

The increasing interest in the evolution of human language has led several fields of research to focus on primate vocal communication. The ‘singing primates’, which produce elaborated and complex sequences of vocalizations, are of particular interest for this topic. Indris (Indri indri) are the only singing lemurs and emit songs whose most distinctive portions are “descending phrases” consisting of 2-5 units. We examined how the structure of the indris’ phrases varied with genetic relatedness among individuals. We tested whether the acoustic structure could provide conspecifics with information about individual identity and group membership. When analyzing phrase dissimilarity and genetic distance of both sexes, we found significant results for males but not for females. We found that similarity of male song-phrases correlates with kin in both time and frequency parameters, while, for females, this information is encoded only in the frequency of a single type. Song phrases have consistent individual-specific features, but we did not find any potential for advertising group membership. We emphasize the fact that genetic and social factors may play a role in the acoustic plasticity of female indris. Altogether, these findings open a new perspective for future research on the possibility of vocal production learning in these primates.

Melody in my head, melody in my genes? Acoustic similarity, individuality, and genetic relatedness in the indris of Eastern Madagascar

Indris (Indri indri) are the only singing lemurs and produce different types of songs that can be differentiated according to their temporal patterns. The most distinctive portions of the songs are “descending phrases” consisting of 2-5 units. In our study, indri songs were recorded in the Eastern rainforests of Madagascar from 2005 to 2015. All the recordings were made when the recorder operator was in visual contact with the singing social group and by recognizing individual indris using natural markings. Because the individual songs frequently overlap during the chorus, we extracted the pitch contour of 1084 descending phrases using the program Praat. We tested whether the structure of the phrases could provide conspecifics with information about sex and individual identity. We also examined whether the structure of the phrases was related to the genetic relatedness of the indris. The results suggest that the songs have consistent sex-, group-, and individual-specific features. We have also found a sig...