1

The function(s) of a long-distance signal: the orangutan long call

Brigitte Spillmann, Anthropological Institute and Museum University of Zurich Switzerland

Summary of the project Long-distance vocal communication in widely dispersed, semi-solitary species often mediates

individuals’ ranging behavior and social relationships (MacKinnon 1979, Galdikas 1985a, van

Schaik 1999, Mitra Setia, Delgado et al. 2009, Singleton, Knott et al. 2009). Long calls are the

most conspicuous long-distance vocalization in orangutans. They are emitted only by flanged

males. Long calls are audible up to 1 kilometer for human observers on the ground and are

therefore key regulators of encounters between dispersed individuals in a dense rainforest

where visibility is limited (Galdikas 1983, Mitani 1985b). Two functions of long calls are generally

considered: repulsion of male rivals and mate attraction (Mitani 1985a). Nevertheless, long call

function is poorly understood, given that recent work in our group has shown that: (i) there is a

third likely function, travel coordination with non-receptive females (Mitra Setia and van Schaik

2007); (ii) long calls can be divided into acoustically distinct types (Spillmann, Dunkel et al.

2010); and (iii) social systems, and in particular male-male competition and male-female

relationships, differ between Sumatran and Bornean orangutans (Delgado and van Schaik

2000). In this project, we intend to examine all three possible functions of long calls and their

information content on both islands, in order to elucidate the flexibility of vocal signaling in a

geographically variable social system.

We followed focal males to record their ranging, social and vocal behavior, but also established

a network of 20 autonomous digital field recorders (autonomous acoustic monitoring AAM)

throughout the area to get a complete overview of long call dynamics for 24 hours. The

combination of traditional follows and novel auditory monitoring will create an accurate picture of

flanged males’ presence in the area, and thus allow us to reconstruct a model of the

communication network over time and space and the ranging responses of individual males and

females to the long calls of other flanged males. In addition, playback experiments will answer

questions about females’ and males’ reactions to long calls in a controlled way and thus to

elucidating long call function.

As this project is not yet finished results included here refer to the validation of AAM.

Methods and data collected

This project is based on a fine-grained approach (simultaneous follows, recordings of long calls,

playback experiments) and a coarse-grained approach (autonomous acoustic monitoring AAM)

that will be merged together for data analyses.

Field work took place at two field stations: Camp Tuanan (2°09’ S, 114°26’ E) in Borneo

(Indonesia) from February 2012 until April 2013 and Camp Suaq Balimbing (03°02’N; 97°25’E) in

2

Sumatra (Indonesia) from March 2011 until November 2011. Both sites are managed by the

Anthropological Institute and Museum in collaboration with BOSF (Bornean Orang-Utan Survival

Foundation) and MAWAS for Tuanan and Paneco SOCP (Sumatran Orangutan Conservation

Project) for Suaq Balimbing. Both sites are situated in a peat swamp forest and encompass a ca.

700 ha grid based trail system for Suaq Balimbing and 1000 ha for Tuanan.

Unfortunately we faced a lot of difficulties during the first field season in Suaq Balimbing.

Problems stretched from technical equipment that did not work well (recorders, GPS devices) to

low manpower. Technical problems decreased markedly after all recorders were replaced at the

end of 2011. Unfortunately at the same time permits to stay in Suaq Balimbing were rejected

because of elections in Aceh. Therefore we had to remove the whole AAM in Suaq earlier than

intended and had to move the whole equipment to Tuanan field station in Central Kalimantan in

January 2012. This final report includes data from Tuanan.

General Methods

The collection of general behavioral data comprised full day focal follows (nest-to-nest follows)

whenever possible. Activities were recorded on a standardized instantaneous two-minute-scan

mode. Continuous sampling was used to record social behavior (see

www.aim.uzh.ch/orangutannetwork.html). Ranging data of focal animals were drawn on a map

and GPS points were set every 30 minutes. The location of special occasions such as long call

given by a male or long calls heard by a focal individual were indicated on the map and recorded

by GPS, context and direction of long calls were noted for subsequent calculation of ranging

responses.

Since February 2012 until 15th of April 2013 following sex-age classes were followed in Tuanan.

During this 731 focal follows, 506 follows had long call occurrences either heard long calls or

given long calls. Therefore On 71% of focal follows either long calls were heard or given.

Sex-Age Class Focal

follows Follows with LC

flanged males 265 196

unflanged males 52 40

females with dependent offspring 221 148

juvenile male and female 64 35

infants 111 87

Total 713 506

Nineteen different flanged males were followed during these 15 months (Tomi, Helium, Niko,

Fugit, Chili, Otto, Dayak, Kentung, Teju, Katmandun, Dolay, Max, Henk, Preman, Sugus, Tora,

Flunmu, Luca, and Wodan).

3

Long call recordings and analyses

Long calls were recorded whenever possible during focal follows using a shotgun microphone

(Sennheiser ME67) and a recording device (Sony PCM D50 or Edirol R09). Recorded long calls

with high recording quality were used for playback experiments. Measurements of the acoustic

structure of long calls will be taken with acoustic software (Raven, Praat). Frequency and time

measurements of high amplitude pulses at the beginning of the long call and descriptive

measurements that characterize the long call as a whole will be recorded (Spillmann 2008).

We were able to record around 400 long calls given by 15 different flanged males. These

recordings are essential for the identification of long calls recorded by AAM.

Playback Experiments

We conducted playback experiments using recorded long calls from a local flanged male. These

long calls are discriminated between spontaneous and elicited long calls. We will test the

immediate reactions and their delayed ranging responses 30, 60, 90, and 120 minutes after the

playback experiment of females (sexually active and non-active). Additionally, we conducted

playback experiments of unfamiliar flanged males’ long calls (provided by OU Trop) towards

flanged males. GPS points were taken at the playback position and at the position of the

receiving focal during playback experiment and after 30, 60, 90, and 120 minutes. With these

GPS points the subsequent ranging responses of the focal animal will be calculated. Playback

experiments were conducted according the rules of the pilot project in Tuanan (Spillmann 2008).

From October 2012 until April 2013 we were able to conduct playback experiments on eight

females with dependent offspring and seven flanged males. Playback data is not yet analyzed

but will be integrated into AAM analysis as soon as all AAM data is extracted.

Acoustic monitoring

We installed 20 time synchronized recording devices (autonomous digital field recorder SM2+,

Wildlife Acoustics) in a grid of 500 m inter-microphone distances (see figure 1). The initial set up

and installation of the autonomous digital field recorders were supported by a technical

assistant. All positions of autonomous recorders were taken by the integrated GPS device

SM2+. Recorders were on around 20-25 days a month from dawn to dusk and a systematic

changing subset during night. Around 6 Tb raw acoustic data was collected at Tuanan field

station.

A long call recorded by different autonomous digital field recorders shows different times of

arrival of the sound waves and the locality of this calling male can then be estimated through

triangulation. The localized long call position and probably the identity of the male (assuming it is

one we know) makes it possible to gain information about long call distribution over the whole

study area.

With the ranging data of focal follows, the additional data of long calls occurred anywhere in the

study area but now recorded by AAM we are better able to understand the ranging behavior of

orangutan individuals. The aim is to reconstruct the communication network and the ranging

responses of individual male and female receivers.

4

Fig. 1: Grid of recorders (black dots) at Tuanan field site in Central Kalimantan.

AAM data extraction and validation

The procedure of extracting data from the raw recording files of AAM and the subsequent

localization of recorded long calls are shown in the flux diagram below. We validated the

procedure with 89 known long calls (flanged males that were followed).

Fig. 2: Flux diagram of procedure of long call extraction and triangulation. Step 1 indicates long call extraction from recorded sound files. Step 2 shows the cross-correlation procedure to get time of arrival differences of the sound waves at different recorders. Step 3 is the triangulation of these arrival delays to obtain the position of the long call.

5

Step 1: A trained recognition algorithm recognized 143 long calls out of 145 long calls that were

given by flanged males during focal follows where time and position of the long calls were known

(Agranat 2009).

Step 2 and 3: Long calls that occurred in the area bounded by microphones show a mean

triangulation error of 51 meter. Sound Finder a program that uses least square solution to

estimate the position of a sound provides an output with the coordinates of the location of a

longcall and an error (ms). Low errors represent triangulations with high accuracy whereas high

errors (ms) represent unreliable triangulations (Wilson, Battiston et al. 2013).

We compared triangulation accuracy of long calls occurring inside the grid versus outside the

grid and found as farther outside the grid a long call occurred as worse was the localization

accuracy (Spearman’s rank correlation: rho = 0.596, p < 0.05) and the error output of Sound

Finder does not predict reliably the localization accuracy of a triangulation. These finding reflect

results of other studies on acoustic localization (McGregor, Dabelsteen et al. 1997, Mennill,

Battiston et al. 2012). Therefore only rough estimations are possible for long calls occurring far

outside the grid (>200 m, see fig.3).

Fig. 3 Correlation between positions of long calls occurred in relation to the distance of the long call position and the microphone grid. Triangulations with low errors (<200 ms) established by the software (red dots) and triangulations with high errors (blue dots) are shown in the graph.

Preliminary results of AAM

I am not yet able to show results of AAM in combination with focal follow data because I am still

extracting and localizing long calls. But below you see a map of the acoustic landscape of a

single day including focal follow data of a flanged male and a female with dependent offspring

(Fig. 4). This map only visualizes data that will be available when AAM data extraction is

finished. Red stars indicate triangulated locations of long calls, whereas yellow stars are rough

6

estimation of long call positions. Pink arrows indicate the travel direction of the female with

dependent offspring (Desy) and blue arrows the travel direction of the flanged male (Teju). In a

next step we want to identify localized long calls to make the picture more complete.

Fig. 4: Map of a single day including all long calls occurred and the ranging data of a female with dependent offspring and a flanged male.

Conclusion

The validation of AAM shows that we are able to draw maps of the distribution of long calls over

time and space. We think that a mean triangulation error of 51 meter in a dispersed system

where mean inter-individual distances range from 500-730 m is accurate to draw conclusion

about orangutans ranging behavior to long calls (Mitra Setia, Delgado et al. 2009). Anyway, the

triangulation error is here defined as the distance between the acoustic localization of Sound

Finder and the GPS position of a corresponding long call recorded during focal follow. GPS

handheld show an error of around 8-12 meter at Tuanan field site, and observer take GPS points

at a distance of around 5-20 meters away from their focal animal. These errors may improve or

worsen the accuracy of the results obtained by triangultion.

AAM in combination with focal follow data is a powerful tool to understand the social

organization of orangutans by examining their long-distance communication system. This

approach may bring the study of social communication in dispersed systems such as that of

orangutans to a new level of sophistication.

7

Acknowledgments

I am grateful to the Indonesian Ministery of Science and Technology (RISTEK), Director General

Departemen Kehutanan (PHKA), Departemen Dalam Negeri, TNGL Medan, and the BKSDA

Palangkaraya for permission to carry out research in Indonesia and to the Universitas Nasional

(UNAS) for support and collaboration and particularly Pak Tatang Mitra Setia and Dr. Suci Utami

Atmoko. I thank the Bornean Orangutan Survival Foundation (BOS) and MAWAS in

Palangkaraya and the Sumatran Orangutan Conservetion Project (SOCP) for their support and

permission to stay and work at both sites.

I thank Carel van Schaik for giving me the opportunity to carry out this project and for inspiring

advice and discussions. I thank Mure Wipfli for his technical support (not only in the field) but

also his moral support when things did not work as expected. In the course of this project

several people were involved in discussions and brainstorming many thanks to Maria van

Noordwjik, Erik Willems, Hjalmar Kühl, Oliver Wagner, Marta Maser and Simon Townsend.

Many thanks go to students and volunteers Alie Ashbury, Markus Lütscher, Sofia Forss,

Caroline Schuppli, Tom Green, Piero Amodio Anna Marzec, Stephanie Mercier, Bonnie Evans,

Meret Heidmann, Zoe Maxon, Alysse Moldawer, Hamdani, Joandini, and Tomi. Special thanks

to all field assistants and staff of both field sites: Pak Rahmatd, Idun, Abuk, Tono, Suwi, Kumpo,

Suga, Ilo, Nunik, Pak Jubai, Pak Nandi for Tuanan, and Herman, Izumi, Fikar, Toni, Armas,

Mahmudin, Pak Rustam, Pak Syafi’I, and Pak Ishak for Suaq Balimbing.

I am grateful to James Askew and Helen Morrogh-Bernard, from OuTrop for providing recorded

long calls from Sabangau field site to be able to conduct playback experiments. I thank my

family and friends for supporting me during my work in the field and now back in Switzerland.

Thanks to the University of Zurich for financial support and the foundations that supported this

project financially: Leakey Foundation, Basler Stiftung für biologische Forschung, and Giacomi

Foundation.

References:

Agranat, I. (2009). Automatically identifiying animal species from their vocalizations, Wildlife Acoustics Inc., Concord, MA. Delgado, R. A. and C. P. van Schaik (2000). "The behavioral ecology and conservation of the orangutan (Pongo pygmaeus): A tale of two islands." Evolutionary Anthropology 9(5): 201-218. Galdikas, B. F. M. (1983). "The Orangutan Long Call and Snag Crash at Tanjung Puting Reserve." Primates 24(3): 371-384. Galdikas, B. M. F. (1985a). "Adult male sociality and reproductive tactics among orangutans at Tanjung Puting." Folia Primatologica 45(1): 9-24. Lameira, A. R. and S. A. Wich (2008). "Orangutan Long Call Degradation and Individuality over Distance: A Playback Approach." International Journal of Primatology 29(3): 615-625.

8

MacKinnon, J. (1979). Reproductive behaviour in wild orangutan populations. The Great Apes. D. A. Hamburg and E. R. McCown. Menlo Park, CA, Benjamin/Cummings Publishing Company: 257-273. McGregor, P. K., et al. (1997). "Accuracy of a passive acoustic location system: empirical studies in terrestrial habitats." Ethology Ecology & Evolution 9(3): 269-286. Mennill, D. J., et al. (2012). "Field test of an affordable, portable, wireless microphone array for spatial monitoring of animal ecology and behaviour." Methods in Ecology and Evolution 3(4): 704-712. Mitani, J. C. (1985a). "Mating-behavior of male orangutans in the Kutai Game Reserve, Indonesia." Animal Behaviour 33(MAY): 392-402. Mitani, J. C. (1985b). "Sexual selection and adult male orangutan long calls." Animal Behaviour 33(FEB): 272-283. Mitra Setia, T., et al. (2009). Social organization and male-female relationships. Orangutans geographic variation in behavioural ecology. S. A. Wich, S. S. Utami Atmoko, T. Mitra Setia and C. P. van Schaik. Oxford, Oxford University. Mitra Setia, T. and C. P. van Schaik (2007). "The response of adult orang-utans to flanged male long calls: Inferences about their function." Folia Primatologica 78(4): 215-226. Singleton, I., et al. (2009). Ranging Behavior of orangutan females and social organization. Orangutans Geographic Variation in Behavioral Ecology and Conservation. S. A. Wich, S. S. Utami Atmoko, T. Mitra Setia and C. van Schaik. Oxford, Oxford: 205-212. Spillmann, B. (2008). Female's reaction to context-dependent long calls of flanged males in Bornean orangutans (Pongo pygmaeus wurmbii). Anthropological Institute and Museum Zurich, University of Zurich. Spillmann, B., et al. (2010). "Acoustic Properties of Long Calls Given by Flanged Male Orang-Utans (Pongo pygmaeus wurmbii) Reflect Both Individual Identity and Context." Ethology 116(5): 385-395. van Schaik, C. P. (1999). "The socioecology of fission-fusion sociality in orangutans." Primates 40(1): 69-86. Wilson, D. R., et al. (2013). "Sound Finder: a new software approach for localizing animals recorded with a microphone array." Bioacoustics 23(2): 99-112. Website (Standards and Methods): www.aim.uzh.ch/orangutannetwork.html