ontogeny of squirrel monkey calls under normal conditions and under acoustic isolation

Ontogeny of Squirrel Monkey Calls under Normal Conditions and under Acoustic IsolationAuthor(s): Peter Winter, Patricia Handley, Detlev Ploog and Ditmar SchottSource: Behaviour, Vol. 47, No. 3/4 (1973), pp. 230-239Published by: BRILLStable URL: http://www.jstor.org/stable/4533549 .

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ONTOGENY OF SQUIRREL MONKEY CALLS UNDER NORMAL CONDITIONS AND UNDER ACOUSTIC ISOLATION

by

PETER WINTERt, PATRICIA HANDLEY, DETLEV PLOOG and DITMAR SCHOTT1)

(Max-Planck-Institute for Psychiatry, Laboratory of Primate Behavior, Miinchen, West Germany)

(With 4 Figures) (Rec. I5-VII-I972)

INTRODUCTION

An important question arising in the study of social communication is to what extent social signals are innate or learned. At present, there exists no exact information to what extent the development of acoustical signals in primates is dependent on species-specific auditory input.

In the case of birds, however, investigation of this question has lead to the following results (NOTTEBOHM & KONISHI, in GALAMBOS & WORDEN,

I972): I) Some birds (e.g., domestic fowl) will produce the species-specific call even if deafened at birth prior to exposure to the call. This implies a pre- wired, genetically determined model for a call production. There is no

process of matching to an auditory input. 2) Some birds (e.g., song sparrows) can develop the normal song even

though raised in isolation from it, but, if deafened at birth, the normal song fails to develop, suggesting the auditory feedback from their own song production is necessary, presumably for matching with a template. 3) In the third type of ontogeny, not only is auditory feedback necessary, but also an external "model" of the correct song must be presented to the

developing bird. For example, chaffinches raised in isolation have abnormal

songs which lack much of the structure which forms when they are ex-

posed to the species-specific song during development. The first attempt to solve this question in primates was made by RIGGS

t deceased, March Io, 1972. I) The authors are indebted to Dr EDUARD F. EVANS for stimulating discussions and

his perusal of the manuscript.



ONTOGENY OF SQUIRREL MONKEY CALLS 231

et al. (I972) who examined the effect of deafening on the vocalization of the adult squirrel monkey. This study showed that there was no apparent difference in the quality of the vocalizations of the deafened animal and that of the normal one. We conclude from this that the squirrel monkey, therefore, does not need acoustical feedback in order to maintain the proper species-specific vocalizations. However, the question remains unanswered whether the vocal repertoire is innate or is imprinted at some stage in the animal's development. Or, phrasing the question more cautiously: is species- specific auditory input necessary for the proper development of this species' complete vocal repertoire. The hypothesis of an innate vocal repertoire was

put to a direct test by raising infants born of muted mothers in acoustic isolation. The vocalizations were compared with those of normal (not acoustically isolated) neonates.

MATERIAL AND METHODS Seven infants of the Brazilian variety of Saimiri-sciureus were the main subjects

of this study (59 9 and 28 8). They are listed in Table I along with additional information. The data from these infants (B, D, F, H, J, L, N) make up the bulk of the experimental information. This is supplemented, however, by less regular and less extensive information acquired from E, Fe, M, X, I and 0. Two of the infants (B, D) were brought up under normal conditions (exposed to species-specific communication). The additional infants F, H, J, L, N, whose mothers were muted, were brought up in an environment free of any species-specific auditory input. In addition, L underwent a deafening operation 5 days after birth (and died in the 4th month of life before the full extent of the observation- and recording period was terminated).

The mother of J died 12 days after birth. Since that time the baby was hand-raised outside the laboratory 2). O's mother died at birth. The newborn was isolated less than 24.00 hours after birth and hand-raised up to its accidental death by asphyxiation at the age of 21 days.

Experimental procedures are outlined in Table i. The mothers of F, H, J, L, N underwent the following muting operation. One to two months before delivery, the pregnant animal was anesthetized with an i.m. injection of 20 mg/kg Ketamine (Parke- Davis). The aditus laryngis was washed with diluted (I/Io) solution of Pantocain (Hoechst) in order to inactivate its reflexive closure at mechanical stimulation. The vocal folds were removed using a laryngoscope, scissors, and electrocoagulation. Post- operatively, the animals were observed several days for vocal utterances. Although, the animals attempted to vocalize in the appropriate context, those utterances were unstructured, uniform and noise-like.

Method of observation.

During the first recording sessions, mother-infants pairs wer!e isolated. After 14 days, mother-infants pairs (E and F, G and H, K and L, and M and N) were placed within visual and auditory contact with one another. After six months, the mothers

2) Thanks to the enthusiasm and skill of Mr and Mrs SCHMITZ, J not only survived but also showed acceleration of physical development as judged from the continuous increase of body weight.



232 \\'INTER, I-ANI)DLEY, Pl' OG (&. SCHOTT

were removed and the isolates remained together in a group. The infant J remained in social, acoustic, and visual isolation until after two months of life. Under these conditions, all recordings were taken with an Uher Report 400-L tape recorder at the speeds indicated below using an Uher microphone. The voice commentary of the observer situated close to the animals was recorded simultaneously. Whenever possible, the recording environment was muffled for the damping of sound reflection. Special care was taken to reliably identify the vocalizer.

TABLE I

experimental infant sex date of birth procedure comments

E $ 8.11.I970 SO Fe $ I5.II.1970 SO M $ I0. 8. 967 SO X $ 6.11.1965 SO I 8 24.IO.1965 SH handraised from day I9;

died 24.12.1965 0 9 28.IO.I97I SH handraised from day 2;

died I5.11.I97I B 9 I0.10.I970 N D 9 20.IO.I970 N F 8 Io. 8.I97I I mother muted I4.6.I971 H 9 22. 8.I97I I mother muted I4.6.I97I N 8 30. 9.1971 I mother muted 25.8.1971 J $ 26. 8.1971 IH mother muted 9.7.I97I

handraised from 9.9.1971 L 9 26. 9.1971 ID mother muted 25.8.I971

deafening operation 30.9.I97I

SO = supplemental observation in a normal group; SH = supplemental observation, handraised; N - normal development; pregnant mothers separated from group 6-4 weeks before delivery, kept in separate rooms with their infants up to 6 weeks after birth, then back in collective holding facilities. After 3 months of age, infants were separated from mothers; I = isolation from specific auditory input; mothers muted 6-4 weeks before delivery, 4-3 weeks before giving birth mothers were removed from laboratory to an environment free of any species-specific auditory input. At 14 days of age first contact with conspecific isolates; after 3 months, separation from mothers. Termination of isolation at 8-Io months of age; H = handraised; D = deafened.

In order to get as complete a spectrum of vocalizations as possible, an average of between 4-6 observational hours per day were made for infants B, D, F, H, J, L, N during the first week of life. In these cases, the mothers were adapted to the conditions of observation several weeks before birth so that the on-going activities seemed not be inhibited by a strange environment.

During the first month of life, an observation session lasted for 200 min: Ioo min of continuous recording of all on-going behavior at low speed (4.7 cm/sec) and Ioo min recording concentrating on bursts of vocal activity employing high (9.5 or I9 cm/ sec) speed recording. After the first month, the animals required a short period of familiarization before actual recording took place. The subsequent sessions lasted from between 30-120 min until Io to 20 cackles, peeps, and trills, respectively, were recorlded.



BEHAVIOUR XLVII (1973): 232

, f I J

'p 1 - - - -

I /

a, A . 4W-

c d *

-

i.-; c _

/ ;x: C : . , '' ........

.: A, I,

0

'-V

0 -.

0-

5 -

0 -

5-

0 -

ic

st .

-1 t '1

I I

3

a

. I 05 s.

C d S I 9

5-

:IL 0-

Fig. i. Spectrographs of vocalizations of a normal infant at the first day of life (left) and within the first week (right). The individual spectrograms are arranged to follow the logical development of the vocalizations into the 3 major groupings. Group i is comprised of peep and twit type calls including combinations with shriek. Group 2 includes all calls with most of their fundamental frequencies below I kHz, i.e. essentially cackling type calls including transient twit (2d, e) and noisy components (2i, k). Group 3 consists of err type calls together with twit (3e, f, g) and cackle (3a, c) combinations. All calls are analyzed with narrow band filtering (45 Hz) except id, e; 3c (lower), d, e, f, g. h which were analyzed with wide band filterng (3co Hlz). Nomenciature of the calls: Ia, b, c: isolation peeps; id: isolation peep with shriek component; Ie: low frequency shriek with peep component; if, g, h: short peeps; Ii: vit; Ij: twit; ik, 1: alarm peeps; im: location trill. 2a: eh; 2b, g: cackle; 2c: yow; 2d: oink; 2e, f: kecker; 2h, i, j: yapping; 2k, 3a: rough cackle. 3b: spitting; 3c: transient between err and cackle; 3d: grumbling; 3e: transient between err, grumbling and short peep; 3f, g:

err-chuck combination: 3h: purring.

P LATE V

:;:00::;



: i :i:

c 0

Fig. 2. Upper sequence: - Isolate N: first day of life. Typical call types from a sequence of vocalizations associated with locomotion activity

and orientation towards the observer. a, f, g: isolation peeps; b, h: twit-like, transition to location trill; c, d: yapping; e: kecker-like call. Narrow

band analysis: c, d, e; wide band analysis: a, b, f, g, h. Lower sequence: - Infant L : deafened, isolated monkey. Typical call types from a

sequence of vocalizations associated with breast feeding at 3 days of age. a, b: rough cackling; d, e: transient err-grumble; c, f, g, h:

grumble: i: grumble (narr-w. band analysis of call h); j: cackling with upward inflection of frequency at the center part of the call. Narrow

band analysis: a, b, i, j; wide b analysis: c, d, e, f, g, h.

0 C: frI

V

'.4

to-1 to



BEHAVIOUR XLVII (1973): 232

a b

RHz

10-

0-

10

0 - O - - - ... ....... . ......._... . . -

10-

0o-

Fig. 3. Natural sequence of isolation peeps uttered by normal infant D when separated from mother at 2 months of age. Sequence shows variations of isolation peeps, which can be associated with changing behavioral states: a, b, c, g, h infant in locomotion;

d, e, f, i, j no positional changes during peeping.

PLATE VII

d c

0-108-24.12

I.

-t

*"N

m

.7




Evaluation of data.

Vocalizations were analysed by a Kay Electric Sonagraph Mod.: 606I B using both narrow and wide band filter settings. Spectrograms were made of the entire sequence of calls so as to avoid biasing the data by inadequate sampling. The data were divided into convenient time periods (s. below) and the spectrographic analysis was terminated when a minimum of 15 vocalizations of each of the more frequent call types were analysed. Time and frequency measurements were then made from the spectrograms. According to WINTER (I969), one can assume a Gaussian distribution of the frequency and of the duration of the calls, and on this basis the mean (x) and the standard deviation (s)' were calculated (Table 2 and 3).

The data were divided into the following time periods: I = Ist week; II = beginning of 2nd week to the end of the 4th week; III = beginning of the 2nd month to the end of the 3rd month; IV - beginning of the 4th month to the end of the 6th month; V,= beginning of the 7th month to the end of the 9th month; VI = beginning of the Ioth month to the end of the I2th month; VII = beginning of the I3th month to the end of the I7th month. The "normal" infants were observed through the VIIth period. The "isolated" infants were observed through the IVth period.

RESULTS

(a) Qualitative analysis in normal and isolated infants.

All call types as defined by WINTER, PLOOG & LATTA (I966) except

twitter/trill, were recorded within the first day in both normal and isolated infants. Thus, the following vocalizations are fully differentiated on the

first day: isolation peeps, cackling, yapping, grumbling, shriek, and alarm

peep. The first recordings of location trills were obtained at the third day

(Fig. I). However, it took up to 3 months until the location trill typical for

infants stabilized at its final form, which is similar to a twit-type trill of adult animals. Calls similar to kecker developed in the first week of life

(Fig. I), (WINTER, PLOOG & LATTA, I966). The latest call to develop was the twitter call. The development of twitter/

trill originated from peep type calls as well as cackling calls. The first fully differentiated twitter/trill calls were observed after at least 3 months of life. At 9 months of age, no significant differences from mature vocalization could be detected.

Calls specific for infants up to 3 months of age were grumbling, purring, and location trill, although similar call types have been recorded from adult

monkeys, in different situations. The first occurrence of call types obviously depends on the appropriate

conditions, that is the presence of releasing stimuli and on maturational factors. Since complete isolation of the infants, i.e., from their mothers is

neither possible nor desirable in regard to the problem under investigation, the design of the study does not allow one to separate maturational factors

Behaviour XLVII I5



234 WINTER, HANDLEY, PLOOG & SCHOTT

L<9-218 -26.9 a b c d

kHz

_ -. ,. - _ _

0- - - - ---

* f 9

0- A-----e

h ; i

~~0. s

I ,, 0.5s.c

Fig. 4. Sequence of isolation peeps of deafened isolate L when separated from its mother at 29 days of age. Narrow band analysis. a, b: addition of shriek component at second half of call; c, d, e, f, g, j: variations of the typical isolation peep; h, i: frequency modulation superimposed on fundamental frequence. The picture illustrates possible transitions and variations in a natural sequence of isolation peeps immediately after separation from the mother. Addition of shriek components indicate high degree of excitement (a, b), c-g transitional phase until a fairly stable behavioral stage results,

h-j marked by isolation peeps of fairly constant shape.




from stimulus availability. For the normal infants as well as for the isolates, it is shown that those calls associated with special situations like nursing, clutching, and separation are readily available when needed (Fig. 2 compared to Fig. I).

There is almost no demonstrable development of any of the examined calls, except for the twitter/trill. This development actually takes place towards the middle or end of the 2nd month when the infant starts to become more independent from the mother and begins to eat solid food (PLOOG, HOPF & WINTER, I967).

The 5 animals (F, H, J, L, N) selectively isolated from any species- specific auditory input displayed all aspects of normal vocalization. Even the hand-raised infant J and the deafened infant L did not deviate from the standard repertoire. As an example compare Fig. 3 to Fig. 4. The only discernible difference in fact was reduced frequency of calling. In the case of J, this reduction existed until it came into contact with the other isolates; thereafter, the frequency of calling was within the normal range. However, the frequency of calling in the deafened, isolated animal L, was abnormally low throughout its life. This drop in vocal activity was also observed in some of the deafened adult squirrel monkeys (RIGGS et al., I972).

All calls of the isolates seem to occur in the functionally correct context. By the standards of our observational techniques, mutism of the mother obviously does not interfere seriously with the mother-infant relation.

b) Quantitative analysis. Tables 2 and 3 detail the physical data, i.e., the duration of a call and

its fundamental frequency, analysed for cackles and isolation peeps respectively. This analysis represents 15 calls of each call type recorded in each period. The length of the experiment extended for the normal animals B and D over a period of 15 months; for the isolates F, H, J and N for 6 months, and for L for 3 months. These intervals were respectively divided into the periods indicated (see Methods).

Comparing all animals in Table 2, the duration of the isolation peep increased significantly by an average of I30 msec between the first and last period of observation. On the other hand, the fundamental frequency remained approximately the same. The comparison of the fundamental frequency across animals within any period, also shows no significant difference. This remained the case even though B and D were brought up under normal conditions, and F, H, J and N along with deafened L were brought up with muted mothers and isolated from any species-specific auditory input (Table 2).



TABLE 2 t)

Peep Calls oN

I II III IV V VI VII Period (Ist week) (2nd-4th week) (2nd + 3rd ms) (4th-6th ms) (7th-9th ms) (Ioth-I2th ms) (I3th-I7hms)

Animal Parameter x s x s s x s x s s x s

D (msec) 285 89.I 262 60.6 295 I32.7 282 91.1 269 51.6 374 84.0 320 43.2 ST (kHz) 9.7 1.36 9.9 1.2 9. I 1.9 9.I 1.36 Io.I 1.2 9.3 0.9 IO.O 0.9

MF (kHz) 11.2 1.85 II.8 I.0 IO.O I.I 9.8 0.73 IO.3 0.7 10.5 I.I io.6 0.2 E (kHz) 5.5 I.7 5-7 2.2 7.8 1.8 6.6 2.4 5.9 2.4 5.4 1.4 4.8 0.8 D (msec) 182 26.4 207 27.5 262 94.8 309 118.9 273 59.9 393 57.2 416 65.8 q

ST (kHz) 7.I 2.22 8.I I.7 7.9 1.2 8.5 1.62 9.6 I.4 7.0 0.4 6.7 0.7 y MF (kHz) 9.3 i.6 9.8 1.4 9.7 0.9 9.5 1.19 9.4 o.8 8.6 0.6 8.I 0.5

E (kHz) 8.2 1.15 5.0 I.9 6. i 0.9 9. I .82 7.2 2.4 6.6 I.0 6.9 .o0 D (msec) 220 49.2 297 83.0 379 48.8 343 101.7

ST (kHz) 6. I 0.9 6.8 I.o 7.8 I.0 7.3 .5 MF (kHz) 8.8 0.5 9.5 I.I 10.1 0.3 9.5 0.7

E (kHz) 6.4 1.5 6.6 I.9 7.8 i.o 6.5 x.6 D (msec) 237 85.3 306 94.8 386 44.0 389 66.8 0

H ST (kHz) 7.2 1.2 7.6 I.8 6.3 0.7 6.7 2.6 c MF (kHz) 8.9 0.8 10.5 o.6 9.5 0.9 9.5 I.5 R

E (kHz) 8.0 1.3 6.9 I.I 5.1 0.5 6.2 x.6 m

D (msec) 307 59.1 395 65.I 329 72.2 448 53.6 ST (kHz) 7.2 0.9 8.3 0.9 8.6 2.4 7.0 1.3

MF (kHz) 9.6 0.5 I1.2 0.4 I.5 1.5 9.3 0.5 E (kHz) 7.1 0.9 8.2 I.3 8.3 1.8 6.4 1.3 D (msec) 228 43.7 251 36.8 390 60.8 D = duration

L ST (kHz) 7.0 .o 8.I I.7 7-4 I.2 ST = starting frequency MF (kHz) 10.7 I.4 10.9 1.I 9.I 0.4 MF = mid-frequency

E (kHz) 5-7 1.3 7.I 2.3 4-7 o.8 E = end frequency D (msec) 223 45.1 314 37.4 310 40.2 3I6 79.9

N ST (kHz) 7.7 1.5 9.5 I.o 9.0 I.2 9.2 2.0 MF (kHz) Io.o 0.8 12.2 0.5 II.3 i.o 10.4 I.i

E (kHz) 8.6 I.6 6.9 i.6 6.9 1.8 6.7 2.3



TABLE 3

Cackle Calls

I II III ~~~~~~~ ~ ~~~~~IV V VI VII Period (i st week) (2nd-4th week) (2nd ± 3rd ins) (4th-6th ins) (7th-9th ins) (rioth-12th ins) (i3th-17th ins) '- 0

0 Animal Parameter j s xi s x s S s x ss S

B D (msec) 68.3 23.4 57.7 1[9.2 61.7 26.6 83.1 i6.8 6r.7 29.1I 58.3 16.5 53.3 I1L4 r

MF (kHz) o.6 o.1 0.5 o.x o.6 o.2 0.5 0.1 0.5 0.1I o.6 0.1 0.5 0.1 0

D D (msec) 78.8 29. I 72.7 14.4 64.7 9.9 76.7 22.8 11. 03 58.0 111.9 523 1. MF (kHz) 0.59 0.09 0.56 0.05 0.5 0.05 0.49 0.11 0.5 0.1I 0.5 0.1 0.5 0.04 10

D (msec) 65.3 10.1 74.0 11.7 72.0 15.9 54.3 15.1

MF (kHz) 0.4 0.1 0.5 0.1 0.5 0.11 0.5 0.04

H D (msec) 87.0 29.6 68.3 Io.8 50.3 13.6 68.3 I19.1I H MF (kHz) o.6 o. I o.6 0.1 0.5 0.1I 0.5 0.04

D~ (msec) 57.8 9.0 60.7 14.4 58.3 9.8 65.7 34.80 ME kz o.6 0.2 o.6 0.1 0.5 01 0.5 0.

L D (msec) 76.3 54.7 66.7 20.1I 59.3 I11.0 ME (kHz) 0.52 0.1 o6 0. . 01C

N D (msec) 78.0 4I.i 6o.o 16.7 64.0 r13.9 67.3 r 7.4 D = duration N ME (kHz) 0.53 0.i0 o.6 0.'1 o.56 0.1I 0.52 0.04 ME = mid-frequency

c



238 WINTER, HANDLEY, PLOOG & SCHOTT

Table 3 indicates that there were no significant differences in the duration or fundamental frequency of the cackle within or between any of the indicated periods.

DISCUSSION

We present here clear evidence that the vocal repertoire (as examined

by spectrographic analysis and qualitative assessment of the call's form) of squirrel monkey infants raised under normal conditions and those raised in the absence of species-specific auditory input are virtually identical. Furthermore, comparison of the infant's vocalization with those of adult animals (WINTER et al., I966; SCHOTr, I972) shows no significant differences. The only exception is the duration of the isolation peep, which is shorter in infancy and develops to the adult length in the 6th to 9th month of life. This may depend on the fact that the infant's lung capacity is less than that of adult animals.

Consequently, we can say that species-specific auditory input is not necessary for the development of the vocal repertoire. The hypothesis that the learning of species-specific calls may have occurred at the time when the isolates were put together can be discarded because: a) the vocal development was normal up to the moment of social interaction with other isolates; b) thereafter, the vocal development of the isolates was entirely consistent with that of the normal infants; c) infant L showed no change in vocal development after undergoing a deafening operation.

The fact that infant L was deafened five days after birth makes it difficult to say to exactly what extent auditory or proprioceptive feedback is essential for normal vocal development. However, the normal vocal development and further vocalization of the infant L after deafening leads one to assume that vocalization of squirrel monkeys does not depend on auditory feedback. These results are consistent therefore with the experiment of RIGGS et al. (I972).

In the introduction, three possibilities of the ontogeny of the vocal behavior in birds were presented. The first of these possibilities appears to hold true also for the squirrel monkey; that is, a "pre-wired", genetically determined vocal mechanism. In other words, on the basis of these experiments we can assert with a high degree of probability that the vocal repertoire of the

squirrel monkey is innate. Moreover, the observations of the deafened infant L and supporting data on deafened adults indicate that even the auditory feedback of the animal's own voice is not necessary for the development of the proper calls (PLoOG, I97I).




SUMMARY

Five mothers of squirrel monkey infants isolated from other species members were muted by severence of their vocal cords during pregnancy. After delivery, mother infant pairs were brought up in an environment free of any species-specific auditory input. One of these infants underwent a deafening operation five days after birth. In addition, two infants grew up under normal conditions, i.e., exposed to species-specific vocalization. Supplemental data were acquired from six other infants, four of them normally raised and two handraised. Soundspectrograms were taken over a period up to six months in the case of the isolates and up to 17 months for the normal animals. Samples of this spectrographical material were analyzed with respect to the form of calls and to quantitative criteria, such as duration, starting frequency, mid-frequency, and end frequency of peep and cackle calls. Clear evidence is presented that the vocal repertoire of squirrel monkey infants raised under normal conditions and those raised in the absence of species-specific auditory input are virtually identical. Furthermore, comparison of the infants' vocalization with those of adult animals shows no significant differences.

REFERENCES

GALAMBOS, R. & WORDEN, F. G. (1972). Auditory processing of biologically significant sounds. Neurosci. Res. Progr. Bull. Io, p. 31-49.

PLOOG, D. (1971). The relevance of natural stimulus patterns for sensory information processes. - Brain Res. 31, p. 353-359.

-, HOPF, S. & WINTER, P. (I967). Ontogenese des Verhaltens von Totenkopfaffen (Saimiri sciureus). - Psychol. Forschung 3I, p. I-4I.

RIGGS, G., WINTER, P., PLOOG, D. & MAYER, W. (I972). Effects of deafening on the vocal behavior of the squirrel monkey. - Folia primat. 17, p. 404-420.

SCHOTT, D. (I972). Quantitative Analyse des vokalen Repertoires der Totenkopfaffen (Saimiri sciureus). - Dipl. Arbeit, Naturwiss. Fak. der Univ. Miinchen.

WINTER, P., PLOOG, D. & LATTA, J. (I966). Vocal repertoire of the squirrel monkey (Saimiri sciureus), its analysis and significance. - Exp. Brain Res., I, p. 359-384. (I969). The variability of Peep and Twit calls in captive squirrel monkeys (Saimiri

sciureus). - Folia primat. I0, p. 204-215.

ZUSAMMENFASSUNG

5 tragende Totenkopfaf fen-Weibchen wurden von Artgenossen isoliert und ihre Stimmbander wahrend der Schwangerschaft durchtrennt, um sie zu verstummen. Nach der Geburt der Jungen wurden die Mutter-Kind-Paare in einer von artspezifischen auditorischen Reizen freien Umgebung aufgezogen. Ein Jungtier wurde 5 Tage nach der Geburt vertaubt. Parallel dazu wuchsen 2 Jungtiere unter normalen Bedingungen auf, d.h. sie waren artspezifischen Vokalisationen ausgesetzt. Weitere Daten wurden von 6 anderen Jungtieren gesammelt: 4 wuchsen normal auf und 2 wurden von Hand aufgezogen. Lautspektrogramme der isolierten Tiere wurden iiber einen Zeitraum von 6 Monaten angefertigt, die der normal aufgewachsenen Tiere umfasste 17 Monate. Stichproben dieses spektrographischen Materials wurden analysiert hinsichtlich der Lautform und der quantitativen Kriterien, wie Dauer, Anfangs-, Mittel- und Endfre- quenz der Peep- und Kakellaute. Es wird der Beweis erbracht, dass das vokale Reper- toire der unter normalen Bedingungen und bei artspezifischem auditorischem Reizentzug aufgewachsenen Jungtiere praktisch identisch ist. Ausserdem zeigen sich keine nennens- werten Unterschiede zwischen den Vokalisationen der jungen und der erwachsenen Tiere.



ontogeny of squirrel monkey calls under normal conditions and under acoustic isolation

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