Ecological and Behavioural Factors Influencing Territorial Call Rates for the Bolivian Titi Monkeys, Plecturocebus modestus and Plecturocebus olallae

Abstract

Primate territorial calls have been used to locate groups in censuses. Daily variations in call rates are a potential source of error in these studies. To obtain more accurate estimations of population density it is necessary to determine how much variation there is in group call rates and to identify the factors that influence them. We present data on the emission of territorial calls by two threatened and endemic titi monkeys in Bolivia: Plecturocebus olallae and P. modestus. We found interspecific differences in daily call rates (52% P. modestus and 33% P. olallae). Groups inhabiting more continuous forests vocalized more frequently than groups in fragmented forests, which might be linked to the higher abundance of groups in less fragmented forests. We found seasonal differences in call rates between species, with more frequent calling in P. modestus during the dry season, while P. olallae called more frequently in the rainy season. The study groups emitted territorial calls mostly from the central zones of their territories, suggesting they do not face intense spatial competition with neighbouring groups. Our results improve the general ecological knowledge on P. olallae and P. modestus, and can also be used to improve population abundance studies and ongoing conservation efforts.

Ranging behavior and the potential for territoriality in pair‐living titi monkeys (Plecturocebus discolor)

“…Alternatively, titis might have less need to monitor their borders as they frequently produce loud duets that convey to neighbors and other potential challengers (e.g., dispersing individuals) the occupancy of the callers' home range by an adult pair. In this study, the three main groups called from locations throughout their home ranges, that is, without concentrating their vocal behavior in either border or core areas, which is similar to the pattern seen in Plecturocebus modestus and P. olallae (Martinez & Wallace, 2016) and Callicebus personatus (Price & Piedade, 2001) and is consistent with the idea that these vocalizations are an intergroup spacing mechanism that involves regular announcement of occupancy of an entire home range (da Cunha & Byrne, 2006;Van Belle et al, 2013). It remains to be studied whether loud calls in titis mediate movement decisions (e.g., approaching, retreating) in nearby listening groups, as has been observed in other primates (Bornean gibbon, Hylobates muelleri, Mitani, 1985, mantled howlers, Alouatta palliata, Hopkins, 2013black howlers, Alouatta pigra, Van Belle & Estrada, 2020;grey-cheeked mangabeys, Brown, 2020).…”

“…Both members of a male-female pair engage regularly in long-distance vocalizations (i.e., duets and solo calls) that can be heard over at least 200 m (Gestich et al, 2017) and are produced mainly in the morning (Adret et al, 2018). These calls are presumed to be components of a territorial display and are inferred to be associated with advertisement or defense of a range and/or mates (Caselli et al, 2014;Caselli et al, 2015;Lawrence, 2007;Martinez & Wallace, 2016;Robinson, 1981). However, limited information is available from wild studies about ranging behavior and space use for these small-bodied (~850-1400 g), primarily frugivorous primates (Norconk, 2011).…”

Duetting Patterns of Titi Monkeys (Primates, Pitheciidae: Callicebinae) and Relationships with Phylogeny

“…Because the habituation process of just one family group can take months, methods relying on either auditory detection of loud calls at fixed points or playback of titis’ vocalizations have been used as surrogate techniques for field surveys [ 94 , 118 , 119 , 120 , 121 ]. Better density estimations of cryptic species obtain when taking into account the seasonal variation in loud call emissions [ 93 ] and by combining playback with point transect distance methods [ 122 ]. The present study will make for a better taxonomic identification of titi monkey loud calls and for selecting the appropriate auditory stimulus for playback in field surveys of population densities.…”

“…Bolivia harbors six species of titi monkeys distributed both in the donacophilus ( P. donacophilus , P. modestus , P. olallae , and P. pallescens ) and moloch ( P. aureipalatii and P. toppini ) lineages [ 72 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 ].…”

Pitheciid vocal communication: what can we say about what they are saying?

“…Call playback has already been used successfully for distribution surveys of several titi monkey species, including Callicebus coimbrai (Aldrich et al 2008; Chagas and Ferrari 2010; Jerusalinsky 2013; Jerusalinsky et al 2006; SouzaAlves and Ferrari 2010, Plecturocebus discolor (formerly Callicebus discolor) (Dacier et al 2011) (Gestich et al 2017), and Plecturocebus olallae (formerly Callicebus olallae) (Martinez and Wallace 2016). In all cases, the technique was found to increase the likelihood of encountering the target animals.…”