Vocal communication in wild chimpanzees: a call rate study

BACKGROUND: Patterns of vocal communication have implications for species conservation: a change in calling behaviour can, for instance, reflect a disturbed habitat. More importantly, call rate is a parameter that allows conservation planners to convert call density into animal density, when detecting calls with a passive acoustic monitoring system (PAM). METHODS: We investigated chimpanzee (Pan troglodytes schweinfurthii) call rate during the late dry season in the Issa Valley, western Tanzania by conducting focal follows. We examined the socio-ecological factors that influence call production rate of savanna woodland chimpanzees. RESULTS: We found that sex, proportion of time spent in a vegetation type, proportion of time spent travelling, time of the day, party size and swollen parous female presence had a significant effect on the call rate. Call rate differed among the different demographic classes with subadult and adult males vocalising twice as often as the subadult and adult females and three times as often as the juveniles. APPLICATIONS: The use of PAM and recent statistical developments to estimate animal density is promising but relies on our knowing individual call rate, often not available for many species. With the improvement in automatic call detection, we anticipate that PAM will increasingly be broadly applied to primates but also across taxa, for conservation

Vocal communication in wild chimpanzees: a call rate study.

Background: Patterns of vocal communication have implications for species conservation: a change in calling behaviour can, for instance, reflect a disturbed habitat. More importantly, call rate is a parameter that allows conservation planners to convert call density into animal density, when detecting calls with a passive acoustic monitoring system (PAM). Methods: We investigated chimpanzee (Pan troglodytes schweinfurthii) call rate during the late dry season in the Issa Valley, western Tanzania by conducting focal follows. We examined the socio-ecological factors that influence call production rate of savanna woodland chimpanzees. Results: We found that sex, proportion of time spent in a vegetation type, proportion of time spent travelling, time of the day, party size and swollen parous female presence had a significant effect on the call rate. Call rate differed among the different demographic classes with subadult and adult males vocalising twice as often as the subadult and adult females and three times as often as the juveniles. Applications: The use of PAM and recent statistical developments to estimate animal density is promising but relies on our knowing individual call rate, often not available for many species. With the improvement in automatic call detection, we anticipate that PAM will increasingly be broadly applied to primates but also across taxa, for conservation

Noninvasive Technologies for Primate Conservation in the 21st Century

Observing and quantifying primate behavior in the wild is challenging. Human presence affects primate behavior and habituation of new, especially terrestrial, individuals is a time-intensive process that carries with it ethical and health concerns, especially during the recent pandemic when primates are at even greater risk than usual. As a result, wildlife researchers, including primatologists, have increasingly turned to new technologies to answer questions and provide important data related to primate conservation. Tools and methods should be chosen carefully to maximize and improve the data that will be used to answer the research questions. We review here the role of four indirect methods—camera traps, acoustic monitoring, drones, and portable field labs—and improvements in machine learning that offer rapid, reliable means of combing through large datasets that these methods generate. We describe key applications and limitations of each tool in primate conservation, and where we anticipate primate conservation technology moving forward in the coming years

Acoustically assessing apes: chimpanzee conservation with passive acoustic monitoring

With one million species at risk of extinction, there is an urgent need to regularly monitor threatened wildlife. In practice this is challenging, especially with wide-ranging, elusive and cryptic species or those that occur at low densities, such as chimpanzees (Pan troglodytes). Monitoring is needed to establish conservation actions, but also to assess population trends. For conservationists, key questions concern species distributions and densities. These data must be regularly updated, allowing conservation planners to effectively execute and assess conservation efforts. Conservationists benefit from methods that are time- and cost-efficient and simultaneously provide accurate and precise data. I evaluate passive acoustic monitoring (PAM) as a tool for detecting, localising, and estimating densities of chimpanzees. I compare with results from camera traps (CT), a more common method. I deployed two arrays of acoustic sensors in Issa Valley, Tanzania: one comprising twelve non-GPS-synchronised acoustic sensors across the whole study area for nine months to estimate chimpanzee presence/absence and density. I simultaneously deployed 53 CT for methodological comparison and used spatial capture-recapture (SCR) and distance sampling (DS) methods. Another acoustic array comprised four custom-built GPS synchronised acoustic sensors, deployed for a 3-month period around a single valley (~2km2), to localise chimpanzees. I found chimpanzee detectability varied over seasons. It is five times faster than an equivalent method using CT. Furthermore, I found that the estimated density of calling chimpanzees with acoustic SCR was lower than density derived from SCR with CT data, but within the 95% CI obtained with DS and CT data. Playback sounds were localisable with 27 ± 21.8m error and chimpanzee calls were localisable within 52m from the location of a researcher following the calling individuals. These results suggest PAM is a promising non-invasive method for chimpanzee monitoring. Despite the current challenges to automate data analysis, improvements of automatic call detection are promising. I anticipate that PAM will become more common in the conservationist’s toolbox for loud calling terrestrial species monitoring such as chimpanzees, gibbons, orangutans, wolves or elephants