Orangutan Night-Time Long Call Behavior: Sleep Quality Costs Associated with Vocalizations in Captive Pongo

Researchers have suggested that the ability of male primates to emit long-distance vocalizations is energetically costly and potentially incurring important adaptive consequences upon the calling individuals. Here, we present the first preliminary data on captive orangutan (Pongo spp.) nocturnal long calls, generated at the Indianapolis Zoo. We used videography to characterize long calls with observed behavioral contexts for 48 nights (816 observed hours totaling 83 long calls). We generated somnographic data for a subset of the long calls. Overall measures of sleep quality generated by infrared videography were then compared to the somnographic, nocturnal long call data. We tested hypotheses related to the proximate mechanisms involved in the initialization of vocalization and the potential costs of emitting long calls to overall sleep quality. We found that (1) performed long calls were conscious and premeditated in nature and (2) greater number of night-time long calls shared a positive relationship with arousability and sleep fragmentation and a negative relationship with total sleep time and sleep quality. These findings strongly suggest that only several minutes of total time invested in long calls throughout the night disproportionately cost the caller by negatively impacting overall sleep quality. 1. Introduction Several nonhuman primate species are known to emit “loud calls.” These alarm call vocalizations are like most animal acoustic signals in that they are primarily produced during their active period [1–6] and thus are characterized by species-specific circadian distribution [7, 8]. Given primate loud calls are stereotypically characterized by traits such as acoustic intensity (dB), form type (i.e., length frequency modulation), and often vocalized by high ranking males [9], it has been suggested that Old World monkey and ape loud calls are phylogenetic homologous characteristics [10]. In general, several hypotheses have been forwarded in attempts to explain the function of primate loud calls: mate-attraction, inter-group spacing and intra-group cohesion, and territorial advertisement [11]. Within the repertoire of orangutan (Pongo) vocalizations the long call is characterized by several idiosyncratic traits: it is produced often by large individuals [5, 12–14], it travels greater than 300 meters [15], it has only been observed to be emitted by flanged males [13, 14, 16], it is the loudest call in the repertoire (reaching 100？db at 1 meter away and can be heard up to more than 1？km in distance) and calls may exceed three minutes in length