The major question addressed by this project was to determine if the long-necked,
freshwater turtle Chelodina oblonga, vocalise underwater and whether their vocal activity could
be related to behavioural or ecological aspects of their lives. These turtles often live in
wetlands where visibility is restricted due to habitat complexity or light limitation caused by
factors such as tannin-staining, or turbidity. For many aquatic animals, sound is a useful
means of communication over distances beyond their visual acuity. This thesis gives the
first detailed account of the underwater vocal repertoire of C. oblonga.
In total, over 230 days were spent in the field and more than 500 hours of tape recordings
were made for this research. Initially, a number of recordings took place in three wetlands
known to support turtle populations: Blue Gum Lake; Glen Brook Dam; and Lake
Leschenaultia in Perth, Western Australia; in order to determine the nature of the
freshwater sound field and place turtle vocalisations into the context in which they were
vocalising. The wetlands differed in terms of degree of enrichment, substrate material, water
depth and habitat complexity. Recordings were made over a four-week period in the last
month of summer and the first week of autumn (Feb-Mar 2003). Invertebrate sweeps were
also taken over a two-week period at each recording site to determine if invertebrate
distributions were related to patterns of sonic activity. To determine the influence of wind
on ambient noise; recordings were undertaken on winter mornings (June-August, 2003) at
Blue Gum Lake and Glen Brook Dam at locations north, south, west and east for four
different wind speeds Beaufort Wind Scale (BWS) 0,1,2 & 3.
There were seven distinctive calls recognised in the recordings. The frequency bandwidth
most utilised by organisms was between 3 kHz up to around 14 kHz, with the exception of the bird-like song; which extended from 500 Hz up to around 10 kHz. Blue Gum Lake
contained a more diverse and abundant assemblage of invertebrates than Lake
Leschenaultia and Glen Brook Dam. Correspondingly, a greater diversity of calls was
recorded at Blue Gum Lake, as well as the presence of chorus activity, which was not heard
at the two less-enriched sites. The periods of greatest diversity and abundance of
macroinvertebrates was synonymous with the increased sonic activity at dusk and midnight
with noise levels greatest at dusk in particular, and to a lesser extent at midnight. There was
no difference in ambient noise at Blue Gum Lake or Glen Brook Dam at wind speeds of
Beaufort Wind Scale 0, 1 and 2.
Turtles from three populations were recorded in artificial environments: consisting of
round, plastic, above-ground ponds (1.8m dia. x 0.65m depth), which were set up to recreate
small wetlands. Recordings occurred from September to October, 2003 and from
February to December, 2004 as well as January, 2005. Seven hatchling and five juvenile
turtles (CL <10cm) were also recorded in order to ascertain whether very young turtles
vocalised. Hatchlings were recorded in a glass aquarium (35.5cm length x 20cm width x
22.0cm depth) and juveniles were placed into a below-ground outdoor pond (1m length x
0.5m width x 0.4m depth). Recordings occurred from as early as 4.30am (dawn recordings)
to as late as 1.30am (evening recordings).
The recordings revealed that turtles utilise an underwater acoustic communication system
(calling at the waters surface was also noted but these were not recorded or a part of this
research) involving a repertoire of both complex and percussive sounds with short, medium
and potentially long-range propagation characteristics. Complex structures included
harmonically related elements (richly or sparsely) and different rates of frequency
modulation. Frequency use extended beyond the in-air auditory sensitivity known for a
single species of turtle studied from the family Chelidae; with calls ranging from around 100
Hz in some of the percussive displays, to as high as 3.5 kHz in some complex calls, with
clicks extending beyond the 20 kHz upper limit of the recording system. However, most
of C. oblongas vocalisations had dominant frequencies below 1 kHz. Turtles were
intermittent callers with an extensive vocal repertoire of seventeen (17) vocal categories -
highly suggestive of complex social organisation. Vocalisations included: a) clacks; b) clicks;
c) squawks; d) hoots; e) short chirps; f) high short chirps; g) medium chirps; h) long chirps;
i) high calls; j) cries or wails; k) cat whines; l) grunts; m) growls; n) blow bursts; o) staccatos;
p) a wild howl; and q) drum rolling. Also, two sustained pulse-bouts were recorded during
the breeding months, hypothesised to function as acoustic advertisement displays possibly
calling songs. Hatchling turtles were not heard to vocalise within the audible range. Only a
single complex vocalisation was heard produced by the juvenile turtles, with a number of
percussive calls.
Preliminary playback trials were conducted under free-field conditions and within an
artificial environment, which consisted of a below ground rectangular tank (2.4m length x
0.8m width x 0.6m deep). A number of turtle calls recorded in the artificial ponds were
selected for playback. A UW 30 speaker was used for broadcast of calls. The free-field
playbacks occurred at Mabel Talbot Lake and Blue Gum Lake during the months of April
and May, 2005. Playback using 14 seconds of an artificially constructed sequence from the
sustained pulse-bout occurred in the artificial channels. This sequence consisted of some
of the first phase pulses followed by a section of the vibrato.
The preliminary free-field playback trials indicated that turtles had some interest in the calls
being played by responding with an alert posture. Turtles were shown to remain in the
alert posture for a significantly longer time than when no sound was played or when white
noise was played. The extensive repertoire and initial responses to the free-field playbacks
indicated that sound has some biological importance for C. oblonga, although results of
playbacks under artificial conditions were inconclusive.
| Identifer | oai:union.ndltd.org:ADTP/221776 |
| Date | January 2005 |
| Creators | turtle111@aapt.net.au, Jacqueline Giles |
| Publisher | Murdoch University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.murdoch.edu.au/goto/CopyrightNotice, Copyright Jacqueline Giles |
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