Acciones y Actividades de Fortalecimiento

2.4.1 Study periods

The study was composed of 3 field seasons: two studies of six months each (July- December 2008 and May-October 2009), and a third season in May-July 2010. All observations were recorded during the activity period of the animals (approximately from 5:00 to 18:00 h in the wet season) ranging approximately 11-13 hours a day. I maintained contact with at least one study group for 564, 555 and 176 hours respectively, which corresponded to 85% of the total time (1,530 hours) in the field.

2.4.2 Behavioural data

The usual methods to locate groups were to walk along the trail system and follow vocal cues. Upon finding a group, I collected data continuously (Altmann, 1974) until the focal group was lost or settled in one sleeping tree (ST). When I stayed with the focal group until they were settled on a sleeping tree, I tried to arrive before they left on the next morning and follow the same group for a full day. I did that at least once a month with each group to record the movement pattern and intergroup encounters throughout the day (not presented in this thesis). After having a full day completed I would change to another group the next day, byeither looking for it in its home-range or wait until the previous group had an encounter with a prominent group.

2.4.3 Recording and digitalisation of the vocal repertoire

Recordings were made with a SENNHEISER K6/M66 directional microphone and MARANTZ PMD660 solid-state recorder (44.1 kHz sampling rate; 16 bits accuracy). Any additional verbal comments were later transcribed. All recordings were transferred digitally onto a desktop computer. The auditory and visual categorization of the calls, together with the acoustic analysis were conducted through the PRAAT© acoustic analysis software (Boersma and Weenink, 2005, version 5.1; www.praat.org). In PRAAT, the following spectral settings were applied to measure fundamental frequency: pitch range 500-11,000 Hz, spectrogram view range 0-22 kHz (to determine the number of harmonics) and 0-5 kHz (window length 0.01 s, dynamic range 70 dB).

2.4.4 Behavioural responses during natural and experimental predatory events

General description

After a visual and auditory discrimination of the calls, I then coded and counted the large number of vocalisations produced by these monkeys during the whole time of their vocal responses, or up to the first five minutes after detection of a predator. For each vocal response, the following structural measures were determined:

(a) The total length of the response (in minutes);

(b) The types of calls present during a response to up to five minutes after detection.

(c) The total number of calls during the first minute, and up to the first five minutes after detection of a potential predator. For this I used the tool ‗create a text grid‘ on PRAAT, which enabled me to mark and name all the calls produced in a response(Fig. 2.8). Call rate per individual was calculated by dividing the total number of calls produced in a response to a potential predator, during the first minute after detection and during the first five minutes after detection, bythe number of juveniles and adults in a group at the time of the response.

(d) The proportion of each call type during the first minute and during the first five minutes after detection of a predator. The proportion of each call type was calculated by dividing the number of each call type by the total number of calls produced in a response.

Figure 2.8. Illustration showing call coding and counting, blue bars, depicting 23 B calls in

10.6s.

2.4.5 Vocal data and definitions

To provide a conservative estimate of the repertoire size (during predatory contexts), I used a visual-discrimination method using frequency and time information from the spectrograms to classify calls. Studies on animal communication usually use different terms to refer to and to describe the vocalisations produced by a specific species. In this study I am using the following terms:

Call or vocalisation: the sound produced by the vibration of the vocal cords (Fitch, 2010). It was nominated as having a single or multiple syllables/units. A call was also determined as ―tonal‖ when the fundamental and its harmonics could be seen clearly or ―noisy‖ when the call was harsh.

Harmonics or bands: harmonics bands at integer multiples of the fundamental frequency (as in Rendell et al., 1999).

Syllable: a unit or note usually defined as a sound that at normal intensity makes a single continuous impression, with associated frequency bands (or harmonics), in time on the spectrogram (Eisenberger, 1976).

Simple call: A call of one syllable only. To classify a simple call, I used the criterion that the syllable must have been produced independently of other sounds within a call (not as composite, see below) and be produced by all groups (adapted from Davidson and Wilkinson 2002) (example figure 2.9).

Composite call: According to Robinson (1979a), titi monkeys‘ loud calls have a common pattern of inhalation and-exhalation to produce two or three syllables and a pause. Robinson (1979a) described these type of calls as having: (a) a ―pre- introduction‖ high pitched, quiet, short syllable, followed immediately by (b) a loud, low-pitched ―introduction‖, which are both produced by inhalation, followed by (c) a ―pause‖, and (d) the ―climax‖ produced by exhalation (figure 2.9). Not all multiple calls have all four components and variance will be found in almost all call types. Here, I am considering a composite call as all calls compound of at least two, usually one high- and one low-pitched, syllables (examples on figure 2.10). In most cases, the second syllable would be not produced independently of the first syllable, for instance the ―suffix‖/second syllable of call BS (chapter 3), would only happen after a call B and never by itself.

Series or phrases: a repetition or multiplication of at least two calls of the same type (figure 3.10 chapter 3).

Fre q u en cy (k H z)

Figure 2.9. Components of a composite call with three syllables and a pause (a) ―pre- introduction‖ (b) ―introduction‖, (c) a ―pause‖, and (d) ―climax‖. Classification according to Robinson (1979a).

Figure 2.10. Example of calls of Callicebus nigrifrons showing one simple (one syllable) and four composite (with two or three different syllables) calls.