Quantitative Analysis of the Vocal Repertoire of Squirrel Monkeys (Saimiri sciureus)

Z. Tierpsychol., 38, 225-250 (1975) @ 1975 Verlag Paul Parey, Berlin und Hamburg ISSN 0044-3573 / ASTM-Codcn: ZETIAG

Max-Planck-lnst i tut f u r Psychiatric, Abte i lung f u r Verhal tensforschung, Munchen

Quantitative Analysis of the Vocal Repertoire of Squirrel Monkeys (Saimiri sciureus)

By DITMAR SCHOTT

With 14 figure5

Received: 13. 8. 1973

Introduction

The social behavior of the squirrel monkey has been described in many previous papers (PLOOC e t al . 1963, 1967; MACLEAN 1964; BALDWIN 1968, 1971). This is so complex that, in order to analyse the communication processes, extensive and exact extraction of all signals is necessary. Therefore, for example, the conventional methods used in behavioral observations and experiments, such as recording of sFontaneous behavior o r dummy experiments, are not sufficient here. For this reason, the following method has been developed (MAURUS and PLOOG 1971; MAURUS e t a l . 1972):

In a group of free-moving squirrel monkeys ( two 8 8 , three 99) a social signal was released in one of the animals by means of remote-controlled electrical brain stimulation; the rest of the group responded to this signal. The elicitation of this signal was repeated automatically a t fixed time intervals as often as desired. The stimulus response and the reaction of the rest of the group were silently filmed. The interactions taken from the film evaluation were mathematically analysed (MAURUS and PRUSCHA 1972). This analysis has shown that the variability of the social interactions initiated by repeated stimulation of the same brain site is considerable.

From among all the signals of species-specific conimunicatioii, vocalizations offer the best possibilities for an automated registration and identification of a situation. For the development of such a signal-recognition system, detailed information about the features of the squirrel monkey vocal signals is necessary (PEETZ 1969; MAURUS e t al . 1970).

After the description of the total vocal expressions, further steps into the analysis of the signal function can be taken. This will lead to the question as to which calls function as distinct signals and which are functionally meaning- less variations of a signal.

O n the basis of physical characteristics of vocalizations, WINTER, PLOOG and LATTA established a catalogue of the squirrel monkey’s calls and showed that certain groups of calls, e.g. cackle and err calls, are less stereotyped than

226 DITMAR SCHOTT

others (WINTER et 61. 1966; WINTER 1969a and b). Investigations in a natural environment were presented by DUMOND (1968) and WINTER (1972).

MACLEAN and PLOOG (1963), JURGENS et al. (1967), JURGENS (1969) and JURGENS and PLOOG (1970) investigated the brain structures from which vocalization is elicited. WINTER and FUNKENSTEIN (1971) and WOLBERG and NEWMAN (1972) found neurons in the auditory cortex that respond only to certain components of species-specific vocalization.

None of the publications mentioned contained sufficient data concerning the physical dimensions of calls (frequency and time course), with which the technical development of call recognition will be possible. Accordingly the aim of this paper is:

1. To describe the vocal repertoire on the basis of the call types and their physical parameters;

2. to describe the variability of calls and the transitions between call types on a quantitative basis;

3. to investigate whether or not it is possible to identify each individual’s calls on the basis of physical parameters and to distinguish them from the calls of other group members.

Methods

During the period extending from January 1969 to March 1970, the calls of 19 squirrel monkeys (Saimiri sciuretrs L., gothic type according to MACLEAN [19641) were examined.

The animals were kept three to a cage. The dimensions of the cages were 70 cm X 60 cm X 70 cm. The experimental animals consisted of three groups, each containing 1 8 and 2 99, and two groups with 3 8 8 each. During the month of August 1969, one baby was born in two of the combined groups, and in the third group two babies were born.

Tape recordings of the animals’ calls were made in a room specially equipped for the dampening of sound reflection. During this time the animal was kept in a cylindrical net cage (R = 60cm, h = 50cm). The recordings were taken from one animal alone or together with other species members, according to the means and methods needed to induce vocalization. The animals could be incited to vocalize the following situations:

A. Single animal 1. Space allowing movement 2. I n a net cage

a. Confrontation with a mirror b. Confrontation with a taxodermic model of a monkey in genital display c. Showing of a leather glove used in catching the animals d. Sudden touching of the animal with the hand

3. Confrontation with a strange animal a. Dog b. Snake

a. Regular feeding of animal b. Mornings before feeding c. After not being fed for 24-36 hr d. Showing and then withdrawing food bowl

5. Playing of species-specific calls from tapc recorder

1. Mother and baby

4. Feeding of peanuts

B. Animal together with other species members

a. Baby on the back of mother (riding position) b. Baby off of mother inside net cage c. Baby nursing from mother

a. A submissive animal of the same species in the same cage b. A group member in neighbouring cage

other group member

2. Feeding of peanuts

3. Experimental animal located at a distance of 2-3 m from the cage containing the

Quantitative Analysis of the Vocal Repertoire of Squirrel Monkeys 227

a. Species member visible and audible b. Species member only audible c. Species member incited to vocalize by species-specific tape recordings

4. Spccies members from other groups are located a. in the cage of the experimental animal b. in a neighbouring cage.

In all situations, the calls could be clearly identified as originating from the experimental animal.

The calls were recorded with a directional microphone (Sennheiser M K H 805) and taped with a UHER 4200 stereo tape recorder. To obtain an optimal tone modulation, the calls were taped at the same time on two tracks, each with a different recording sensitivity.

In the second experimental stage the calls were converted into frequency-time and frequency-amplitude diagrams by means of a sonograph (Kay Electrics 6061 B). A 45 Hz band-pass filter was used for all diagrams. Only for the “err” calls, with the exception of E.3”’, was a 300 Hz band-pass filter used. To maintain a more accurate time analysis, a few vocalizations (err calls) were depicted on an oscilloscope and photographed. 6120 calls were evaluated according to the criteria of optical form (shape of call), frequency, duration and the relation of intensity between the fundamental frequency and the overtones.

Definition of the ternis “cal1”and “call type”: Vocalizations with a time interval up to and including 200 msec are defined as a call. Within one call type, the calls which havc similar o tical shapes are pooled (frequency-duration-diagram). The differentiation according to opticarshape - meeting technical requirements - was carried out as fa r as possible (these may but must not be biologically significant).

Results

The vocal repertoire consists of 52 call types which can be divided into six groups. They are termed cackle, err, shriek, peep, trill (WINTER et ul. 1966), and bark calls ( JURGENS 1969).

In the following, the call types are represented by the first letter of the call group and a number (e.g. K. l ) .

Cackle calls (Fig. 1 and 2, K. 1-9)

Within this term all those calls are included which have a fundamental frequency of between 150 and 730 Hz and overtones. The cackle calls can be subdivided into nine different call types. The first five are characterized by the shape of their fundamental frequency, the remaining four by a smearing (unclear differentiation) or by variation in the intensity of the harmonics.

The shape of the fundamental frequency is predominantly horizontal in K.l, ascending in K.2, descending in K.3, ascending then descending in K.4, and descending then ascending in K.5 (Fig. 1). O n the average, the call types have a fundamental frequency of 430 Hz. The decrease in intensity from the fundamental frequency to the first harmonic is - 6 dB, from the fundamental frequency to the second harmonic is -5 dB, to the third harmonic -7 dB, and to the fourth harmonic - 11 dB. The average duration of these calls is approximately 65 msec. All calls belonging to call type K.l have a difference of less than 50 Hz between the highest and lowest points of the fundamental frequency.

The increase and decrease within the course of the fundamental in K.2, K.3, K.4 and K.5 can be so faint that these call types overlap with K.l (the fundamental of which is horizontal). Moreover, there are calls included in K.2, the fundamental frequency of which drops slightly towards the end. These form a transition to K.4. Those K.2 calls, the fundamental frequency of which decreases slightly a t the beginning, form a transition to K.5. Similar transitions

DITMAR SCHOTT

60- L P - 3,O -

a - 1,s-

10-

- A \

- -

Zcif I x c l

x a b c D 1. 2. 3. 4. ms Hz Hz Hz Hz dB dB dB dB

80 380 420 470 90 -6 -5 -8 -11

300 boo 6 6 0 130 2 7 0 +6 +9 +9 +8 30 200 260 300 50 -25 -24 -29 -29

50 70 70 a 0 4 0 5 5 8 8

uu- 60- L.0- $0- Lo- 1,s-

ZCl t I Y C I x a b c D 1. 2. 3. 4. ms Hz Hz Hz Hz dB dB dB dB

80 430 530 450 110 -6 -2 -7 -11 20 80 110 80 60 5 6 5 6

170 6 0 0 7 0 0 600 300 +3 +9 +4 + 4 4 0 220 260 220 50 -16 -19 -19 -23

- -

rcc" - -

I 6 2 dL 46 0,E zctt I Y C I

x a b c D 1. 2. ms nz nz HZ n z dB dB 65 480 440 400 8 0 -7 -5 25 60 6 0 50 20 5 5

150 650 boo 550 130 +3 +8 30 350 320 300 50 -15 -13

60 -1

3. 4. dB dB -7 -13 5 5

+8 +3 .18 -23

n=38

Zeit ( x c l

x a b c D 1. 2. 3. 4 . ms Hz Hz Hz Hz dB dB dB dB

95 500 410 500 lo0 -4 - 4 -5 -9 55 6 0 50 70 40 4 4 6 6

250 700 560 720 200 +4 +4 +5 +3 40 400 320 4 0 0 50 -20 -14 -15 -23

Fig . I

Errata to F igs . 1-12: Frequenz = Frequency; Zeit = Time.

Fig . f and 2: Cackle calls. a = frequency at the beginning of the fundamental tone in Hz; b = frequency in the middle of the fundamental tone (or the highest or lowest frequency) in Hz; c = frequency at the end of the fundamental tone in Hz 1.2.3.4 - The relation of the intensity between the fundamental and the 1st harmonic (overtone), the fundamental and the 2nd harmonic, etc. expressed in dB, whereby + d B

x = duration of the call in nisec;

Quanti ta t ive Analysis of the Vocal Kepertcire of Squirrel Monkeys

K. 6

n=176

x a 1. 2. 3. 4 . m s Hz d B d B d B d B

S 2 0 8 0 4 5 4 6 max 2 0 0 600 t6 +1 o + 4 m i n 20 200 -15 -19 -21 -19

M 60 4 0 0 -8 -8 -7 -7

..= sl . _

Z N l I ~ l

K.6 S.6 K.6'

M S max m i n

Zcil isecl

x a 1. 2. 3. m s Hz d B d B d B

55 230 +12 +6 +6 25 4 0 4 5 5

5.6

4 . d B

+5 4

40 330 +19 +13 +15 +11 20 150 +5 - 4 -3 o

Z o t i y c l

x a b c D ms n z HZ HZ H~

M 95 490 660 530 180 S 15 30 80 50 6 0 max 130 530 760 600 260 m i n 6 0 430 530 430 60

229

Zeil IYCI

E.3/K.3 E.3 E.3'

K.9

K . 9

n=6.4

x a 1. 2. 3. 4 . m s Hz d B d B d B d B

M 35 4 4 0 -12 -14 -12 -11 S 20 50 5 9 11 8 max 120 540 +3 t6 0 - 4 m i n 20 250 -18 -26 -26 -23

Fig . 2

nieans increase of intensity and -dB means decrease of intensity of the overtones in contrast to the fundamental D = the difference between the highest and lowest point of the fundamental frequency in Hz; t i = number of investigated calls; ni = means; s = standard deviation; max = maximum value; min = minimum value Except for K.6', the frequencies of all cackle calls are logarithmically applied (presented). I n the representation of call types K.l-5, K.S and K.9 there is a frequency-amplitude diagram beside each of the

corresponding calls

230 DITMAR SCHOTT

exist from K.3 to K.4 and from K.3 to K. 5. Consequently, these five call types are not clearly defined, but are intermingled with one another.

The call type K.6 differs from K.l by a larger number of harmonics, which in this case become noisier. K.7 differs in the same way from K.4 (Fig. 2 and 12). The transition from K.l to K.6 and K.4 to K.7 is continuous. The cases described above were only occasionally seen in the call types K.2, K.3 and K.5. The acoustical effect of such call types is scratchy.

The call types K.1-4 develop into: I . P.11 and P.12 (see peep calls); 2. T.4 and T.5 (see trill calls).

The call types K.6 and K.7 develop into: I . S.1 and S.2 (shriek calls) by a lengthening of the call and an increased

noisiness of the overtones; 2. S.6 by a shortening of the call, increase in the noisiness and an unrhythmic

repetition of the call; 3. B.4 and B.5 (barking) by a lengthening of the call, an increase in the

noisiness and an abrupt beginning (Fig. 11 and 12). Calls belonging to K.8 differ from other cackle calls in a decrease in the

fundamental frequency (230 Hz) and a weaker intensity of the fundamental than that of the first harmonics (Fig. 2 ) . Calls belonging to K.9 are characterized by the short duration (35 msec) and sharp decrease in intensity of the harmonics against that of the fundamental frequency.

K.8 and K.9 are transitions from the cackle calls to the err calls. This is particularly clear in the comparison of K.9 and E.3, in which E.3 is nothing more than a rhythmic series of short calls of the type K.9 (Fig. 2, K.9 and E.3’ - logarithmic; Fig. 3, E.3 and E.3‘ - linear).

Cackle calls arose in the following situations: I . When the animal was frightened by a sudden touch (human hand, stick)

or by the holding up of a leather glove which is used to catch the animals; 2. when an animal made a genital display towards his own reflection in a

mirror (PLOOG et ul. 1963) or when he grasped the head or waist (PLOOG et al. 1967) of a lower-ranking animal (K.l-9, in addition to shriek and err calls);

3. when confronted with a dog or snake (K.l-7, also barking, and to some extent shrieking).

Err calls (Fig. 3)

The call types E.l to E.4 are characterized by a series of noisy elements (click) that have a maximum intensity of between 0.5 and 2 k H z (Fig. 3).

E.l differs from E.2 and E.3 in that it has a greater number of elements (on an average 35 as opposed to 10 or 5) and in that the frequency range of the maximum intensity is higher (on an average 1 kHz as opposed to 0.6 kHz). Mostly E.4 is combined with T.6, which is a type of trill call (Fig. 3, E.4).

When comparing the maximum or minimum values for the duration of element (x), the frequency maximum intensity (b) and the number of elements (A), it is obvious that the transitions from E.l to E.4 are continuous.

Moreover, E.3 develops into: 1. S.6, by an increase in the frequency range, the duration of the elements

and the distance between the elements (Fig. 3, E.3”, Fig. 5, S.6); 2. S.1 and S.2, in that the frequency range is increased and the elements

fuse together (Fig. 3, E.3”’); 3. K.9 (see cackle calls).

Quantitative Analysis of the Vocal Repertoire of Squirrel Monkeys

I 4 2 Q,L 0,6 98 1.0 Zcit Isccl

x y a b A m s m s kHz kHz

M 4 17 2.6 1,o 35 s 2 6 1,8 0.5 16 max lo 40 8.0 2.0 60 min 2 lo 1.5 0.5 6

0.1 Zeit(sec) x y a b A m s m s kHz k u z

M 9 1 2 6.6 0,6 5 S 5 6 3.4 0,4 4 max 20 30 16.0 2p 28 min 3 3 1.5 0,s 2

I ' 0,2 Z C l l I s r c l x y a b m s m s kHz kHz

M 4 16 2,3 0.6 s 2 6 0.6 0.4 max lo 30 4,O 20 min 3 lo 2.0 0,s

E.3 t

n=96 ai a2 a3 a&

Zeit (ur)

x y a b m s m s kHz kHz

M 7 lo 6,9 1,9 s 4 6 3,3 0,3 max 15 30 12,o 2,o m i n 2 2 2'0 q5

A

1 0

32 3

a

A

12 11 45 2

231 - . ...

E.2

n = l l

E.4

n=55

E. 3/K. 3 E.3 K. 9 E.3 E.2 S.6 I21

E . 3 " '

PI 02 Q3 94 Q5 0.6 0.7 0.8

ZClI (uc)

E.3 / S.1

F l g . 3 : Err calls. y = average distance between the elements of the call in mscc; a = the ceiling frequency in kHz; b = range of the highest intensity in kHz; n = number of investigated calls; m = means; s = standard deviation; max = maximum value; min = minimum

value

x = average duration of the call in msec;

A = number of elements within the call;

232 DITMAR SCHOTT

S . l

S . 1 ‘

5 . 3

a1 03 a3 QL 95 0.6

zen(scc)

x y a b c m s m s kHz kHz kHz S . 3 , S . 4

M 4 1 0 2 1 0 4 , l 4.4 2.9 n=23 S 2 0 5 1 7 0 2,2 42 l,O max 1 5 0 560 lop 1,5 5,o m i n lo 2 5 2,o 2,5 1,5

91 02 93 9L 95 0.6 07

Zric(uc)

x a m s kHz S . l , S . 2

M 380 5,O S 2 0 0 1,6 n=98 max 1 9 0 10,o m i n 6 0 2,o

0.1 0.2 0.3 9L a5 0.6

Z e i l ( u c )

ai w a3 QL 95 0.6

x b c m s kHz kHz

Zeit(sec)

M 300 49 3,3 S 9 5 1,l 1,3 Kmx 410 6,5 5,5 min 1 4 0 3,s 2.0

Fig . 4

s . 2

s.4

s . 5

n= 6

F i g . 4 and 5 : Shriek calls. y = duration of the call components, that i n S.3, S.4, S.7 and S.8 develop out of the range of greatest intensity in nisec; a = range of the greatest intensity of the call in kHz; b = the highest frequency point of the call components’ fundamental and of the call type S.5 in kHz; c = the lowest frequency point of the call ccmponents’ fundamental and of the call type S.5 in kHz; n = number of investigated calls; ni = mean; s = standard deviation; max = maximum value; min = minimum value . Because there existed no difference in the duration and frequency range

between S.1 and S.2 as well as S.3 and S.4, they were combined

x = duration of the call in msec;

Quan t i t a t ive Analysis of the Vocal Repertoire of Squirrel Monkeys 233

0.1 a2 0.3 44 0.1 0.2 03 44 45 05 0.7 0,8 09

ZCll (SKI Zcit (yc)

S . 6 s.l 5 .6 x a m s kHz

M 2 5 6,? S 11 1,3 max 50 11,o m i n l o 2,o

a1 a2 0,3 44 a5

x y a b c ms ms kHz kHz kHz

M 9 0 5 5 6.5 7#2 5,3 S 5 0 3 0 42 2,1 1,l max 2 5 0 180 10,o l z o 8,o m i n 3 0 2 0 4,0 4,O 4,O

Zril (uc)

I . 3 -.

3.

4.

5.

0.1 0.2 0.3 44 Q5 46 07

2Clt 1%)

x y a b c m s m s kHz kHz kHz

M 3 6 0 110 6,5 8,7 4,3 S 330 1 1 5 o,? 2,9 1,7 max 1 1 6 0 4 0 0 8,o 13,o 9,o m i n 80 l o 5,o 4 p 2,o.

Fig. fi

Err calls occurred in the following situations:

shortly before (E.2) and during nursing of bab,y by its mother (E.1); when a monkey made a genital display towards its own reflection in the mirror o r grasped the hcad c r waist of a lower-ranking animal (E.2, E.3, in addition to shrick and cackle calls); whcn the dominant animal - separated by distance but not completely separated from the remaining members of his group - was fed. Also when a hungry mother with her baby was isolated from the group (E.2, E.4 and trill calls); when the dominant animal, which had been separated for approximately one hour from his group, regained visual and acoustical contact with the remaining group members and was a t this time fed (E.3, E.4, in addition to trill calls); when a d was near a P in estrous, he uttered calls of the types E.2, E.4 and T.6

234 DITMAR SCHOTT

Shriek calls (Fig. 4 and 5)

The call types S.l and S.2 consist of a continuous range of noise that extends from 0 to 10 k H z and above, with an average intensity peak of 5 k H z and an average duration of 380 msec. These differ from one another only in that S.2 is intermingled with cackle components (Fig. 4). S.5 consists of an irregular fundamental and its harmonics. The acoustic effect of this call is squeal-like.

The call types S.4 and S.3 form the transition from S.l and S.2 to S.5. These arise because S.5 directly follows maximum intensity range of S.l and s.2.

The call type S.6 presents an unrhythmic series of short shriek impulses (elements), the ceiling of which is 15 k H z and the peak intensity of which lies a t 6.7 kHz. The duration of the elements is on the average 25 msec, while the distance between reaches from 30 to 90 msec; their number varies between 1 and 11 (Fig. 5 ) .

Through a broadening of the elements and a decrease in distance, S.6 develops into S.l (compare with S.6'). A t the maximum intensity range of the S.6 elements, an S.5 (with similar, irregular fundamental with its harmonics) is joined to form call type S.7. O n the basis of its generally higher fundamental frequency (7.2 in comparison with the 4.9 k H z of SS), this call type develops into the peep call group.

Within S.8 are all the calls which develop out of shriek and trill calls. The range of maximum intensity of S.l, as well as the highest and lowest frequency point of the fundamental of the trill call T.l-3, corresponds to the data under S.8 (Fig. 5).

1. 2.

3. 4.

1.

2 . 3. 4.

5.

6.

and

The shriek develops as follows: S.1-3 and S.6 develop into cackle calls (see cackle calls, Fig. 1 and 2 ) ; S.l and S.6 develop into err and bark calls (see err and bark calls, Fig. 3 and 11); S.7 develops into peep calls (see peep calls, Fig. 6-8); S.8 develops into trill calls (Fig. 9). The shriek calls were uttered in the following situations: By higher-ranking animals in connection with head- and waist-grasping, suppression of lower-ranking animals, and occasionally biting (S.l, S.2 and S.6, in addition to cackle and err calls); when an aniinal was held in the hand (S.l, S.2); by a monkey which suddenly attacked a dog (S.1, S.2); during a confrontation with a snake (S.1-5, in addition to cackle and bark calls); when a monkey made a genital display towards a mirror reflection or d o t h e r species member (S.6, S.7, in addition to S.l, S.2, cackle, err and peep calls); by higher-ranking animals when fighting over food (S.6, S.8, in addition to S.l, S.2, cackle, err and trill calls).

Peep calls (Fig. 6 to 8)

The peep calls are characterized by a fundamental frequency (between 2 14.5 kHz1 with harmonic overtones. The duration of the call varies

between 20 and 970 msec. Occasionally the fundamental is interrupted by pauses up to 50 msec (see Fig. 6, P.3).


P . l

4- n=69 0.1 0.2 03 QL Q5

zcll~secl x a b c d D A m s k n z kHz kHz knz knz

M 3 8 5 7,4 9,o 9,8 8,6 2,7 1 S 1 4 5 1,8 2,o 2,l 1,8 1,o max 7 2 0 10,5 13,o 1 4 , O 12,o 5,o 4 m i n 170 4,o 5,o 6,5 1,5 1,o 1

4 . . . . . - . -.- n=287 0.1 0.2 03 QL 05 0,6 0.7

Zen1 (WC)

x a b c d D A ms kHz kHz kHz kHz kHz

M 4 2 0 8,8 9,4 8,4 6,5 3,2 2 S 1 2 0 1,4 1,1 1,2 1,7 1,5 m a x 970 1 4 p 12,5 11,o lop 7,O 5 m i n 1 6 0 4 p 4 5 4 0 2,5 1,o 1

8 ----_I_

- P . 4

n=922

- 2 6

g 4

g 2 P . 3

0.1 0.2 03 Q4 Q5 n=42

0.1 0.2 03 QL

x a b c d A m s kHz kHz kHz knz

X a b c d D A ms k n z kHz kHz kHz kHz

M 3 4 5 8.1 a,5 a,5 7,7 2 M 4 0 0 7,9 10,l 140 7,l 3.7 1 S 1 2 5 2.0 1,5 1 ,4 1,9 S 11 5 2,o 1,8 1,8 1,8 1,5 max 720 11,o 12,o 11,o 1 i,o 5 m a x 8 3 0 12.0 14,5 14,5 12 .0 9,o 4 m i n 160 4,5 5 5 5,5 4,5 1 m i n 1 6 0 3,O 4.0 45 3.0 1.0 1

f---

P . 5 P . 6

n = l 3 0 n=139 m 02 03 44 a5 01 a2 Q3 QL

Zcit (XI Z C l l ( W C )

x a b c d D A x a b c d D A ms kHz kHz kHz kIlz kHz m s kHz kHz kHz kHz kHz

M 360 7*6 9,3 9,2 6.5 3.0 1 M 230 4,7 7.0 6,7 4.9 3,0 2 S loo 1,5 1.3 1,4 1,5 1,3 S 4 0 1.2 1,3 1.7 1,6 1,0 m a x 690 11,o 12,o 12.0 140 6.0 6 m a x 3 5 0 9,o 11.5 12.0 1l.o 6.5 3 m i n l o o 3,5 3,5 4,o 3,o 1,o 1 m i n l o o 2,o 2,s $0 2.0 40 2

F i g . 6

The peep calls are divided into 19 different call types. The f i rs t 10 are distinguished by the duration and the shape of the fundamental frequency. The remaining are characterized by their close correlation to other call types.

236

14.

12.

10.

8

DITMAR SCHOTT

L

'

P . 7

n = 9 7

Z e i l ( s o 4

x a b c d D A m s kHz kHz kHz kHz kHz

S 3 5 1,8 1,9 2,o 2,l 1,3 max 150 11,5 11,o 12,o 12,5 6,o 3 m i n 2 0 2,o 3.5 4,o 3,5 0,5 1

M 6 0 5,a 6.7 i , 4 a,o 2,3 1

41 a2

P . 9

n = 4 0

zeit (set)


M a 5 5.6 5.5 5.4 5,4 0,2 1 S 3 0 2,4 2,4 2,4 2,4 0,4 max 1 5 0 11,5 11,5 11,5 1.1,5 0,s 3 rnin 2 0 2,5 2,5 2,5 2,5 o,o 1


M 5 0 1,5 6,7 6,o 5.3 2 2 1 S 3 5 2,o 1,5 1,3 1,2 1,3 max 150 13.5 11,o 9,o 8,0 7,o 2 min 2 0 3,o 3,0 2,5 2,5 0,s 1

a1 02 Z e i t k )


S 30 2'5 2,7 2,3 2,l 1,2 max 1 5 0 11,o 14,o 12,o 1I.o 6,o 2 min 30 2,o $0 3,0 30 0,s 1

M a 0 5,a 7,i 7,3 5,a 2.2 1

Fig. 7

The fundamental frequency is predominantly ascending in P.l and descending in P.2; is horizontal in P.3; ascending and then descending in P.4; ascending, horizontal and descending in P.5; and ascending, and after a pause of 50-200 msec, descending in P.6 (Fig. 6).

In order for a call to be placed within call type P.3, it is necessary for the difference between the highest and lowest point of the fundamental frequency to be less than 1 kHz.

The ascent and descent of the fundamental frequency in P.l, P.2, P. 4-6 can be so faint that these call types resemble P.3 (compare values under D). Furthermore, there are calls within P.l, the fundamental frequency of which drops so sharply a t the end that it carries cver to P.4. Similarly, some calls within P.2 carry over into P.4 when the fundamental frequency a t the beginning rises sharply. By a more definite ascent and descent and a lessening of the horizontal part, P.5 develops into P.4. Calls within P.4, the middle segment of which contains an interruption of about 50 msec, develop into P.6.

The calls P.7-10 differ from P.l-4 by a shorter duration and a mid- frequency of the fundamentals, which is about 2 k H z lower. The difference

Quan t i t a t ive A n d y s i s of the Vocal Repertoire of Squirrel Monkeys

a1 az a3

Zeit(sec)

x a b c d D A ms kHz kHz knz kHz kHz

M 2 2 5 3.9 6,o 5, i 3 , i 2,a 2 S 45 0.9 1.4 1.4 Lo 1,o max 290 6.0 8.0 8,o 5,5 5,0 4 min 1 3 0 2p 2,5 2,5 2,o 1,5 2

P . 1 3

n=87

14.

12.

1 0

237

0.1

Z t l l (xc)

x a b c d D A m s knz knz knz kHz kHz

M a 0 3,i 4,4 5,i 5.6 2,0 1 S 2 0 0,s 0,6 O t l 0,l 0.5 max 110 4,5 5,o 6.0 6.0 15 1 rnin 4 0 3 0 $5 4,o 4,s 1,0 1

a1 a.2 a3

Zrit hec)

x a b c d D A ms kHz k n z knz knz knz

M 2 1 5 5,2 1,5 1,5 5,l 3,2 1 S 1 2 5 1,l 1,4 1,6 1,3 1,2 m a x 4 7 0 ap io ,o 9.5 a,o 5,o 4

P . 1 4 P . 1 5

- . n=17 n=16

a1 02 Zeic(uc) Zeit (uc)

x a b c d D A x a b c d D A ms knz kHz knz kHz kHz ms kHz kHz kHz kHz kHz

M 7 5 4,6 5.1 5,9 6.6 2,2 1 M 1 9 5 8.0 7 2 i,i 5,i 2,6 2 s 5 5 1.0 0,a 1,0 1,0 I,O s 9 5 0,9 0.8 LO 0,a 0,a rnax 280 6,o 1,o ap 9,o 4,o 1 max 330 10.0 9,o 9,o 1,o 40 3 min 4 0 3,O 4,O 4,5 4,5 1.0 1 min 50 6p 6,o 5,o 4,O 1,5 1

Fig. 8 s = dura t ion of call in msec; F i g . 6 , 7 and 8:

frequency in k H z ; of t he fundamen ta l f requency in k H z ; difference bctween the highest a n d lowest points of the fundamen ta l f requency; of call segnicnts separated by pauses;

Peep calls. a = s t a r t of the fundamental c = two-thirds

D = A = number

s -7

b = one-third of the fundamental f requency in k H z ; e = end of the fundamen ta l tone in kHz;

n = number of investigated calls; m = means; s t anda rd dev ia t ion ; max = maximum va lue ; min = minimum value

238 DITMAR SCHOTT

between the highest and the lowest points within the fundamental frequency of horizontal call type P.9 is less than 0.5 kHz. A comparison of similar criteria from the illustrations of P.7--10 with those of P.l-4 shows that these call types have continuous transitions (Fig. 7). The maximum duration values of P.7--10 flow into those minimum values of P.l-4; therefore, fluent transitions exist here. too.

By ihythmic repetition of the call type P.10, it develops into the trill call (T.2).

The call types P.ll and P.12 form a transition between the cackle and peep calls. This transition arises from the fact that a peep-type component develops out of one of the harmonics of thc cackle. According to JURGENS (1969), by a rhythmic repitition of the call type P.12, it develops into the trill calls T.4 and T.5.

The call types P.13--15 develop into the group of shriek calls. Either the well-defined fundamental frequency of the peep call (P.4) is more and more displaced by noise (P.13), or a peep call develops (P.14, P.15) within the highest intensity range of a shriek call (example: S.6).

The call type P.19 develops into bark calls (see bark calls and Fig. 11 and 12).

Peep calls were uttered in the following situations: 1. When the animal had absolutely no more contact, or only acoustical con-

tact, with other members of his species (P.1-5); 2. by a dominant animal whose cage was located 3 m from other male

members of his group (P.6-11 and P.13); 3. when an animal made a genital display towards his mirror reflection or

a species member (P.7-10, P.12, P.14 and P.15, in addition to cackle, err and shriek calls);

4. by a baby who attempted to remount its mother’s back and was hindered by a net separating them (P.13 and P.14).

Trill calls (Fig. 9 and 10)

These consist of a repetitive, sharply ascending and descending fundamental frequency with harmonic overtones; in addition, a periodical fluctation of the intensity is characteristic.

The difference between the lowest and highest points within a periodic oscillation of the fundamental frequency (a period) is on an average approximately 6 kHz. The frequency range of the fundamental lies between 1.0 and 13 k H z (Fig. 9, T.4). O n an average, the first period is 1 k H z higher and 5-10 msec shorter than the last period. The number of periods within one call varies between 1 and 14 (Fig. 9, T.l, T.3).

The call types differ from one another by the location of their maximum intensity. This is found in T.l in the lower range of the period, in T.2 in the upper range, and in T.3 in the upper and lower ranges. Calls exist within T.3, the upper or lower maximum intensity of a period of which is so poorly formed, that the call type passes respectively over to T.l or T.2.

The call types T.4 and T.5 develop from trill calls into cackle calls. This happens because a t the beginning, during or a t the end of a period a cackle develops (see also description P.12). T.5 differs from T.4 in that each period contains a cackle. By an increase in the cackle calls, T.4 develops into T.5 (see T.4’). T.3 develops into T.4 by a formation of a cackle a t the beginning


10 'i

Zcit (uc) x y a b c d D A ms m s kHz kHz kHz kHz kHz

M 80 a 5 4,3 a,9 3,5 8.3 5,6 4 s 10 1 5 1.2 0,9 1,l 1,o 1,2 2 max 1 2 0 1 6 0 8,0 13,O 7.0 12,s 10,o 1 3 m i n 5 5 55 1.5 6,o 1.5 2p 1,5 1

. n=112 . .- - .. -- . 0.1 0.2 03 QL 0.5 05 1

Zell (set)

x y a b c d D A ms ms kHz kHz kHz kHz kHz

M 6 5 7 5 2,8 8,3 2,l 1,O 6,4 7

max 9 5 1 1 0 5 ,010 ,o 5 , 0 1 0 , O 8 , 0 1 4 m i n 5 0 5 0 1,5 6,o 1'5 4,0 5,o 2

s 10 1 5 0,a 0.6 0,s i,3 03 2

T . 2

n=48 0.1 02 0.3 QL

ZCil (uc)

x y a b c d ms m s kHz kHz kHz kHz

l o 1 5 1,l 1,l 0,8 1,6 loo 1 2 0 6,o 10,5 5,o 10,o

7 0 7 5 2,5 8.3 2.3 7,i

5 0 50 1,s 6,o 1,5 4,O

D A kHZ

69 4 1,o 2 a,5 7 4,O 2

- d

n=49 0.1 02 Q3 94 QS

Zell ~uc)

x y a b c d D A ms ms kHz kHz kHz kHz kHz 7 5 85 3,2 9,o 70 1,l 1,2 6

110 1 2 0 55 13,o 5p 10,o 11,o l o 5 5 5 5 2,o 6,o 1,o 2,5 5.5 2

10 2 0 1,l 1,l 05 1,9 0,9 2

T . 4 ' x y a b c d D A x a b D ms ms kHz kHz kHz kHz kHz m s kHz kHz kHz

M a0 a0 1.9 7,6 i ,9 6,3 5,a 3 a 0 i,9 7,i 5,3

max 1 2 0 130 5,o 12,5 4,s l 0 , O 10,s 9 110 4.5 l 0 , O 9,0 S l o 1 5 05 1,4 0,s 1,s 1,4 1 1 5 0.4 l,O 1,l

m i n 3 0 30 1,o 4 p 1,o 2,5 2p 2 3 0 1,O 5,s $0

Fig . 9

F i g . 9 and 10: Trill calls. y = duration of the last call period in nisec; b = lowest frequency of the first period in k H z ; d = lowest frequency of the last period i n k H z ; D = difference between the highest and lowest points of the fundamental frequency in k H z ; n = number of investigated calls; ni = mean; s = standard deviation; niax = maximum value; min =

minimum value

s = duration of the first call period in msec; fi = highest frequency of the first period in k H z ;

c = highest frequency of the last period in k H z ;

A = number of call periods;

240 DITMAR SCHOTT

P . 1 6

n=lo4

0.1 0.2 03 QL

Zrll (uc)

x a b c d D A m s knz k n z knz knz knz

M 2 2 5 7,3 9,9 10~3 10,o 3,4 1 S 5 5 1,l 1,5 2,l 1,4 1.5 max 4 3 0 11.0 12,o 13.0 12,5 7.5 2 min 1 l o 5,o 7,o 6,5 4 p 1.0 1

P . 1 7

n = l o ::k Zcit Ql 1%) Q2 03 Q4 95 - - - 0.6 OJ


M 90 7,9 80 8,o 8,6 0,7 1

max 1 7 0 8.0 8.0 85 9 p 1.0 1 min 5 0 7,5 8,o 7,5 8,o 0<5 1

S 45 0,2 0 0,3 0,4 0,2

T . 7

41 9 2 Q3 QL 45 0.6

ZCll lscc)

x y a b c d D A m s ms kHz knz knz kHz knz

M 9 5 loo 5.4 9.9 4,4 8,9 5,6 3 S 1 5 15 0,8 1,o 0,8 1,o 1,i 1 m a x 1 4 0 1 5 0 7 ,012 ,o 6.011,o 8,o 7 min 6 0 6 0 1,5 8,o 2,o 6,o 2,5 1

0.1 Q2 0,3 QL 9 5 0,s

Zcit (%I


M 280 6,9 8,8 6,8 8,9 2,8 2

max 4 8 0 8,5 140 8,o 10,o 4#0 3 min 1 l o 5,o 7,o 5,o 8,o l,o 1

S 110 0,9 q 9 0.7 0,s 1,O

F i g . 10

or end of the call. T.2 develops into T.5 by a formation of cackle calls between the periods.

The call type T.6 is one period of T.5 and frequently appears together with E.4 (see Fig. 3 , E.4).

The call types T.7 and P.16--18 (Fig. 10) develop from trill calls into peep calls. The short ascent - occasionally followed by a weaker intensity

Quan t i t a t ive Analysis of t he Vocal Repcrtoirc of Squirrel Monkeys 241

descent - a t the end of the fundamental frequency of P.16 offers the first clue that this call is in between the peep and trill calls. From this peep-like call type P.16 there exist t w o possibilities of further differentiation towards trill calls:

1.

2.

1.

2.

3.

4.

5. 6.

A peep call with a fundamental which ascends tcwards the end is rhyth- mically repeated (see P.17) and finally develops into the type P.18 (pe- riodically-ascending fundamental). Directly joined a t the end of the descending portion of P.16 is a repeti- tively ascending and descending fundamental (T.7). Trill calls arose in the following situations: When a monkey had not received any food for 24 hrs o r longer, o r shortly before o r during feeding (T.1-3); when in addition to the above situation a sFecics member was located near the experimental animal and w'is separated from it spatially, bu t not visually o r acoustically (T.l-6, in addition to err calls); when a higher-ranking animal had a disagreement with a group member over the food (T.6, in addition to cackle, err and shriek calls); when the dominant animal of 3 group, after being separated both visually and acoustically for approximately one hour, had contact again with his group members and was fed a t the same time (T.1-6 and E.3, E.4); when a 8 was near a ? in estrous (T.6 and E.4); when a hungry animal which had been isolated from the group was fed (T.1-3, T.7, P.l-5 and P.16--18).

Bark calls

The bark calls consist of a continuous range of noise which extends on an average from 0 to 12 k H z and which has a maximum intensity of 6 k H z and a duration of 120 msec. They have a stronger intensity and begin more abruptly than the shriek calls (S.1) (Fig. 11).

In comparison with B.l, B.2 has a sharply-descending peep (P.19) a t the beginning, which results in a harsher acoustical effect. When B.2 develops a cackle a t the end of the call, it is then termed B.3. When a cackle appears a t the end of B.l , this call is counted as belonging to B.4. When the whole lower part of B.4 is replaced by a cackle, the call is differentiated into B.5.

Transitions exist between all five call types; all are dependent on the extent to which the peep o r cackle within the bark is developed.

The call type B.l develops into S.1 by a slightening of the beginning ab- ruptness and a lengthening of the duration; and develops into S.6 by a shortening and fast repetition of the call. The call type P.19 contained in B.2 and B.3 develops into the group of peep calls (see Fig. 12: natural succession from peep to bark calls). P.19 differs from the other peep calls in that it has an unusually sharp and swift descent (the average difference between the highest and lowest frequency is 8 k H z against 3.5 for other peep calls).

The call types B.4 and 13.5 develop into cackling in that the noise-frequency range in the upper par t of the call is reduced. (Fig. 12: natural succession from cackle and bark calls; see also cackle calls.)

Barking occurred: I . When an animal was confronted with a dog (B.l-5, in addition to cackle

and shriek calls); 2. when an animal was confronted with 2 snake (B.l-5 and P.19, in addi-

tion to cackle and shriek calls).

242 DITMAR SCHOTT

121 -- --

0.l 0.2 Q3

Zcit CUC) x c m s kHz

M 1 2 0 5.8 s 35 1,l max 180 9,o m i n 5 0 2,o

B . l

n=86

B. 2

n=74 Ql aZ 0.3

, Zeit(scc)

x a b c m s kHz kHz kHz

M 1 2 0 12.0 4.8 7.0 S 4 0 2,7 1.1 1,6 max 190 16,o 8,o 11,o m i n 50 5.0 2.0 5,o

B. 4

n=96

ai 0.2

x c d ms kHz kHz

M 1 2 0 6,o 0,45 S 30 1,5 q07 max 1 7 0 lop of10 m i n 50 2,O 4 4 0

P . 1 9

n = l l -I

0.1 0.2 0.3

x a b c F A m s kHz kHz kHz Hz/ms

M 45 11,8 12,9 4,6 300 S 1 4 2,7 2,7 1,2 loo max 80 16,o 17.0 6,o 550 min 3 0 8,o 8,o 2,o 1 2 0

I

... -

B. 3

n=55 Ql QZ

Zeit(sec)

x a b c d ms kHz kHz kHz kHz

M 1 2 0 lq l 4,7 6,4 0.45 S 2 5 3,O 1.0 0,9 0.05 max 180 160 80 10,o 0.50 m i n 6 0 3,o l,o 2,o 0.40

I

0.1 0.2 0.3

x c d m s kHz kHz

M 110 5,90,45 S 30 1,l 0,05 max 1 9 0 8p 9 5 0 m i n 50 zo 0,40

B.5

n = l l

F i g . 11: Call type P.19. x = duration of the call in msec; y = beginning frequency of the call in k H z ; b = highest frequency in k H z ; c = lowest frequency in k H z ; F.A. = frequency decrease between the highest and lowest points in Hzimsec Bark calls. x = duration of the call in msec; b = lowest frequency of the peep call in k H z ; n = number of investigated calls; m = mean; s = standard deviation; max = maximum value;

min = minimum value

a = highest frequency of the peep call in k H z ; d = frequency of the fundamental of the cackle call in kHz;

Quantitative Analysis of the Vocal Repertoire of Squirrel Monkeys

91 02 Q3 Q4

Zrll(I.E)

P. 5

243

P.19 P.19 P.19 P . 1 9 D . 2

91 O2 Q3 Q6 Q5 0.6 0.7 0.8 49

Zril(rrc)

P.19 K. 6 B. 2

::I

a1 O2 Q3 Q6 Q5 0.6 0.1 0.8

Z d t 1 1 . ~ 1

R. 5 K.6 K . l K.6 F i g . 1 2 : above: A natural series of calls that occurs within a change of situation or motivation. 1.call: monkey alone; 2.--8. calls: monkey sights a snake c below: A natural series of 4 calls

from a monkey when confronted with a dog

Interindividual variability Still unanswered remains the introductory question of to what extent one

can differentiate monkeys by their individual style of vocalizing. This question could not be solved by merely identifying individual animals by particular morphological properties of their calls. It was also impossible to identify the

244 DITMAR SCHOTT

call types in relation to sex, age or rank of the animal. The possibility of recognizing the individual by the voice-frequency range, the duration of the call, the intensity of the overtones, or a combination of these criteria still exists.

Three call types were tested. In all, 2216 calls were used. These came from six to nine animals, with 60 to 100 calls originating from each animal.

1. Peep call P.4 (Fig. 6 ) ; 2. trill call T.l (Fig. 9); 3. cackle call K.l (Fig. 1) ;

The following data were thereby analysed: I . the duration of the call; 2. the frequencies which are characteristic for the fundamental; 3. the relation of the intensity between the fundamental frequency and the

first four overtones (cackle calls). After careful examination, it is shown that the distribution of the duration

of all calls in each animal yields a wide diffusion of data. This is also true for the distribution of the relation between the intensity of fundamentals and that of the first four harmonics of the cackle. Therefore, it is impossible to use this data for a statistical analysis. O n the other hand, there was a peak in the relative distribution of the fundamental frequency for each animal. Fig. 13 shows the relative distribution of the frequencies for the cackle calls. Of eight animals, four have a distribution of frequencies with a maximum of 450 kHz and seven a peak within the range of 400-500 Hz. Similarly, there is no reliable difference between 8 8 and OP. Similar relationships can be found in the distribution of the frequencies of peep and trill calls.

Therefore, it is impossible to establish a clear association between a call and an individual by the frequency alone. Consequently, it would not be useful to make further statistical analyses.

% 70

60

50

40

30

20

10

n

250 300 350 400 450 500 550 600 650 700 Hz F i g . 13: Frequency distribution of the fundamental frequency of cackle calls (K.1). Each of the 8 curves represents the frequency range of the cackle calls (K.l) from a monkey (- ??

8) _ _ _ _ _

Quantitative Analysis of the Vocal Rcpcrtcirc of Squirrel Monkcys 245

Discussion

On the basis of the large number of calls that have been studied and the analysis of their physical data, it can be firmly stated that the vocalization system of the squirrel monkey does not consist of discrete call types, bu t of graded ones. There are fluent transitions within a call group (for example: K.1-5) as well as between call groups (for example: K.6 and K.7 to B.5, Fig. 12). This can take the form of a natural succession as a result of one call type becoming more and more similar to another (fluent transition, example: P.1-6 to P.16--18) or by the characteristics of two call types combining into one (“blended” transition, example: K.1-6 and T.2-3 into T.4-6). Fig. 14 is a survey of the most important transitions between call types and call groups. The transitions from cackling to shrieking and from peeping to trilling are predoniinantly fluent (thick lines). The transitions from the peep and trill calls to cackle calls on the one hand and shriek calls on the other are predominantly additive (thin lines); the transition from P.12 to T.4-6 is described by J U R G E N S (1 969).

I n contrast to previous publications (WINTER, PLOOG and LATTA 1966; WINTER 1969a and b), where examples of transitions from cackle to err calls were given, it has been shown by means of a quantitative analysis of the sound spectra that the whole vocalization system of the squirrel monkey is graded. MOYNIHAN (1964, 1966 and 1970), CHALMERS (1968), EPPLE (1968) and MAR- LER (1970) support the theory that stereotype call systems are found in monkeys which communicate with one another mainly by means of auditory signals (e.g., nocturnal monkeys), and seldom by visual signals such as facial expressions and gestures. According to these authors, monkeys with a continuous call system on the whole use auditory and visual signals simultaneously, which avoids misunderstandings. Adult Marmosets, whose vocalizations go up to about 80 k H z (EPPLE 1968), adult Douroucouli, whose vocalizations go up to about 9 kHz (MOYNIHAN 1964) and Mangabeys, whose vocalizations go up to 8 k H z (CHALMERS 1968) utter discrete call types; while chimpanzees, whose vocalizations go up to about 5 k H z (REYNOLDS et af. 1965), Japanese Macaque ( I T A N 1 1963), Rhesus monkeys, whose vocalizations go up to 6 k H z (ROWELL 1962; ROWELL and HINDE. 1962) and Red Colobus, whose vocalizations go up to about 14 k H z (MARLER 1970) use a graded call system. In addition to these, monkeys exist whose vocal repertoire not only consists of discrete calls, but also shows signs of a graded system. Examples of this are the Golden Tama- rin, young Common Marmosets (EPPLE 1968), young Douroucouli (MOYNIHAN 1964), Vervet Monkeys, whose vocalizations go up to about 16 k H z (STRUH- SAKER 1967) and Black and White Colobus, whose vocalizations go up to about 8 kHz (MARLER 1972).

In comparing the call systems of different monkey species, the application of the hypothesis differentiating graded and stereotype call systems should be made with care. As was shown with the squirrel monkey, precise examination of a great number of calls is necessary in order to answer the question of whether the vocalization system is stereotyped or graded.

In this context i t niiist be considered that the authors mentioned above discriminated stereotyped and graded vocal systems on the basis of the call types and the supposed meaning of the signals, while in this investigation this discrimination was done on the basis of call types only. It is evident that the signal meaning of the vocalizations plays an important role in the classification of a vocal signal system into graded or non-graded calls.

246 DITMAR SCHOTT

Table 1: Description of situations in which vocalizations occur. A : own results; B: results from WINTER (+) 1968/69 and DUMOND (0) 1968 Reaction to outside enemy (danger): Holding an animal. (2) Animals were frightened. (17) Beginning of aggressive reaction. (3) Confrontation with dog and attack on him. (4, 1 8 ) Confrontation with snake or cat. (19) Confrontation with flying or other disturbing objects s Disagreement with species members: (20) Between two groups. (5, 21) dealing with dominance gestures. (6, 22) fighting for food. (7: 23) making genital displays towards mirror reflection or species member. (24) baby after rejection by mother Contact with species members: (8) Mother during nursing of baby. (25) Baby during nursing. (9) Mother before baby nurses. (10, 26) 6 during sexual activity. (27) Sitting together. (28) Playing of young animals. (11) Dominant animal, contact with conspecifics possible, is fed. (12) Dominant animal receives, after a I-hour separation, contact with his group and food. (28) Sight of food and eating Separation of animal from species members: (13) Isolated animal receives food. (30) Animal alone. (14, 31) Animal alone but still having acoustic contact. (15) Baby sees and feels its mother but is restrained by a net from assuming its riding position. (16) Dominant animal is separated from 6 6 species

members (3 m distance)

P E.

- N m <

1. K .

. . - - N < w r -

Reaktion to outside enemy [ 1 w i th species B x x x

members l x x r

Disagreement 5 x x r X

X

x x

X

x x

8 1 X

X

x x

x x

x r

Contact wi th species members

X

x x x x

x x x x

x x X

-

Food w-- X X

X

X X

x x x x

Separation f rom 1 species members

Reaction t o outside enemy

w i th species members

B +

+ B @ + b + +

+ * +

+ + + @ + i

+ 0

+ @ +

+

a

i

0

25

Contact w i th 26 species members 27 +

28 + Food 29 I +

Separation from 301

+ a + 0 0

@ C + + + species members 31 1


Sl

. , _: i .’’.?. i ,*..

Since the data are not sufficient for a definition of the signal meaning of the call types, it is only possible to give an approximate description of the motivations and the call types which belong together. This will take place on the basis of comparison of call types and situations in which they occur (Tab. 1). The situations have been divided roughly into four groups.

It can be seen (Table 1A) that with a “response to an outside enemy”, cackle, shriek and bark calls occur predominantly, and that, with a “confrontation with a species member”, err calls in addition to those mentioned above are uttered, with the exception of barking. In situations of “contact with species

B5

P13

- L + L l - Fir. 14: Transitions from cackle calls to shriek

Pl1

I I

and fro; the pecp and trill calls to cackle and shriek calls

248 DITMAR SCHOTT

members”, err calls are characteristic, while i n situations of “non contact”, peep calls are typical. Trills occur most frequently in situations where food plays a role.

Call types which occur in the same situation as shown in Fig. 14 also contain corresponding morphological transitions; for example: a t the first sight of a loose dog, a monkey uttered a cackle and then barked (situation 5). If the dog was near the cage, the cackle increased and the bark decreased. When the dog approached the monkey, the monkey sometimes attacked it briefly while shrieking. According to observations of a group of monkeys not included in the experiments, it can be stated that the vocal repertoire is substantially more variable than is suggested by Table 1A. A comparison with Table 1B shows, for example, that cackling accompanies contact with species members as well as feeding situations.

In the head list of Table 1A, all call types are pooled which always occur in the same situation. Only the call types I<. (1-7), P. (7-10, 12, 14, 15) and T. (1-3) were separately listed because the comparable call types, according to the observation of WINTER (1966/68) and DUMOND (1968), do not always occur together. E.1 was also dealt with as an independent call type by WINTER and DUMOND. In the situation of a baby nursing from its mother (8,25), E.1 was attributed to the baby, while in these observations the call type was uttered only by the mother.

It can be seen that the main part of the call types occurs together with other call types in one situation and also i n different situations. This may be a hint of the possibility that the call types are more graded than discrete according to their meaning.

To what extent it will be necessary for this system of call types to be further differentiated or combined cannot be predicted. ROWELL and HINDE (1962) and GRIMM (1967), for example, are of the opinion that, for the maca- ques, not only the 20-30 named calls are of communicative value, but in particular the transitional calls allow a greater ability to express motivation. Only by a more comprehensive examination could they see a possibility of recognizing the signal value of each call. Also, with reference to squirrel nion- keys, it is possible, by means of an extensive and exact analysis of all communication processes, to recognize which call types convey specific motivation, or which call types present a transition between two motivations or whether the call types present only an intensity range of a motivation.

As is apparent from the results, it was impossible to associate a call with an individual animal by means of the morphological criteria or the analysed data. This is because, for each animal, the duration of the call and the relative intensity of the overtones of the call result in a wide scattering and that the peak distribution of the frequencies overlap one another to some extent.

This negative result is possibly traceable to the methodical difficulty in evoking the same vocalization from different monkeys in a similar situation. Eliciting a constant response to a substitute (dummy), as is described in birds, is not possible with squirrel monkeys and supposedly impossible for the whole primate family.

However, this does not necessarily imply that the monkeys themselves cannot recognize another conspecific by its voice. N o t all potentially significant biological data were recorded. For example, the absolute intensity of the call was not recorded because a constant distance and direction between the microphone and the monkey’s mouth was necessary. A fixation of the animal, which would have been necessary for this, would have made i t impossible to elicit all the different call types. Also, the acoustical resolving power of the squirrel


monkey could be more comprehensive than that of the K a y Sonograph; small oscillations o r small ascents and descents of a call could be important in the identification of an individual. U p to now, no da ta exists on the acoustical discrimination capacity of the squirrel monkey.

Summary

During experiments concerning the communication of squirrel monkeys, it proved to be necessary to construct an automatic apparatus for the idcnti- fication of individual calls (MAURUS et al . 1970).

The aim of this paper was to furnish the necessary da ta to achieve this (frequency, duration and the relationship of the intensity between the fundamental frequency and the overtones). 6120 calls from 19 animals were analysed and were subdivided into 52 call types. It was thereby shown:

1. Tha t the vocal repertoire consists not of the discrete call types assumed u p to now, but of graded ones;

2. tha t thc animals could not be differentiated as individuals on the basis of the particular parameter of their calls. Thc distribution into 52 call types is not neccssarily biologically signifi-

cant. A final statement about the distribution of call types can be made only after the signal value of each call type has becn determined.

Zusammenfassung

In1 Rahiiien der Untersuchungen uber die Koniniunikation der Totenkopf- affen hat sich die Notwendigkeit ergeben, fur die Erfassung der Vokalisation eiii autoniatisches Lauterkennungsgerat zu bauen (MAURUS et al. 1970).

Ziel diescr Arbeit war es, die dafiir benotigten Daten (Frequenz, Lange und Intensitatsvcrhaltnis zwischen Grundton und Obertonen) zu erbringen. 6120 Laute von 19 Tiercn wurden untersucht und in 52 L,autformen untertcilt. Dabei zeigte sich:

1. Das vokalc Repertoire bestcht nicht, wie bisher angenommen, ails vor- wiegend gcsonderten Lautformen, sondern die Lautformen gehen kon- tin u i e r I i ch in ei n an der ube r ;

2 . die einzelnen Tiere konncn nicht individuell an H a n d besonderer Parn- meter ihrer Laute bzw. Lautformen unterschieden werden. Die vorgenoniniene Einteilung in 52 Lautfornien braucht nicht biologisch

sinnvoll zu sein. Eine endgultige Aussage uber die Aufteilung der Lautformcn kann erst an H a n d des Signalwertes jeder Lautform gemacht werden.

Acknowledgement

The author wishes to express his gratitude to Professor D . PLOOG, Director of the Max- Planck-lnstitut for Psychiatry, to Dr. H. DISTEL, Dr. M. MAURUS, Mr. H. PRUSCHA, Mr. H.-G. PI:I:TZ and Ms. P. HANDLEY for their consideration and generous assistance.

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250 D. SCHOTT, Quantitative Analysis of the Vocal Repertoire of Squirrel Monkeys

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Author's address: Ditmar SCHOTT, Neurobiologisches Labor, Psychiatrische Klinik, 34 Gottingen, v.-Siebold-Strafie 5.

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Quantitative Analysis of the Vocal Repertoire of Squirrel Monkeys (Saimiri sciureus)