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programme. This paper provides a description of the
techniques developed at Parco Natura Viva to monitor vocal
behaviour of mothers and infants in the nest. Recordings
were made while a mother-offspring pair from three
different groups were in a nest-box during three different
reproductive seasons (1995/1996/2002).
The nests were placed inside the enclosures eight to fourteen
days before the offspring’s birth. Nests were positioned
over an existing shelf and fastened to the enclosure structure.
A microphone was set in each of the nest-boxes and could be
linked to the tape recorder without entering the enclosure
as necessary. Leaves and twigs were also introduced in
the enclosure to give the female a chance to build the
nest herself. Three out of four females Varecia variegata
variegata and two out of two Varecia variegata rubra
chose our boxes as a nest.
Sample collection and analysis
Recording began as soon as birth of an offspring was noted.
Recordings were made four to eight hours a day during
the first three days during three reproductive seasons.
Recordings were computerised and split in single call files
that were subsequently processed by Praat 4.0 software in
order to extract spectral and temporal measures, including
duration, fundamental frequency, second harmonic, third
harmonic and fourth harmonic. Frequency of vocalisations
was also calculated. Processed signals included 18 ‘trrs’,
69 ‘whines’ and 118 ‘mews’.
Spectogram of the ‘trr’ vocalisation by infants
Sound quality
We compared acoustic structure of ‘mews’ emitted by mothers
inside and outside the nest-box to determine whether
the artificial nest allows for high quality recordings and is
effective in avoiding unwanted changes in acoustic signals.
None of the five parameters differed significantly between
‘mews’ recorded outside and inside.
Research
Nest-box vocalisations
We noticed that both mothers and offspring emitted ‘mews’
(low amplitude contact calls), and ‘whines’ (high frequencymodulated
vocalisations (Pereira et al., 1998; Gamba and
Giacoma, 2001)). We identified an additional vocalisation made
by infants that could not be paired with the ones previously
described. We named it the ‘trr’ vocalisation. Recordings we
made of this vocalisation averaged 488 ms in duration and had
a very low amplitude of 40-60 dB, with no clear harmonic
pattern recognisable. Infants begin emitting ‘trr’ vocalisations
within six hours after the birth and only made this vocalisation
when the mother was in the nest box. We never recorded
this vocalisation outside the nest.
Conclusions
The techniques developed at Parco Natura Viva to monitor
vocal behaviour of mothers and infants in the nest allowed
good quality recording of vocalisations. Spectral and
temporal properties of the vocalisations were analysed to
phonetically describe the vocal repertoires of mothers and
offspring during the first three days after birth. Apart from
already known ‘mew’ and ‘whine’ vocalisations emitted
also by adults, we recorded a previously undescribed call:
the ‘trr’, emitted by newborns only in the nest. Even if its
function is still to be investigated, the ‘trr’ is certainly a
useful indicator of normal development. We recommend
nest-box recording in lemurs as a valuable non-invasive
monitoring tool
and we stress
References
- Gamba, M. and C. Giacoma, 2001.
its potential to
Vocal communication in Lemuridae,
investigate early
new evidences in Eulemur and Varecia.
post-natal behaviour Advances in Ethology, 36. Supplement
of these prosimians. to Ethology. Contributions to the XXVII
International Ethological Conference,
22-29 August 2001, Tübingen, Germany.
- Pereira, M. Seeligson, M.L. and
J.M. Macedonia, 1988. The behavioural
repertoire of the black and white ruffed
lemur (Varecia variegata variegata).
Folia Primatologica 51: 1-32.
Photo: V. Jirousek
EAZA News 43 – 2003
29
July - August - September