Resonance plays a secondary role in amplifying underwater vocalizations of Weddell seals (Leptonychotes weddellii).

Brief description

The date are of the highest amplitudes across the frequency range of Weddell seal tonal trills (an underwater call made by males). Each column presents the results of a frequency amplitude measure that is relative to the highest amplitude of that trill, independent of the frequency at which that amplitude occurs. This removes the influence of the overall amplitude of the call which is influence of the distance the sea was from the hydrophone when the recording was made. Four trill patterns were identified (A - D) and a number of trills not included in the analyses are classed as type X. The X call types were excluded because the original recording was later found to be overloaded or partly masked by ice noises or the calls of another seal. Analysis details are included in the accompanying manuscript.

The accompanying Excel file contain the frequency amplitude measurements of individual trills at two location groups: the Aurora Truning location at the anchorage location of the Aurora Australis near Davis and the other group is a number of breeding groups in the Vestfold Hills.
Variable A is the frequency in Hz,
Variables B to DH at the Aurora Turning location and B to BY at the Davis locations are data from individual trills.
Rows 2 or 3 indicate the four Trill patterns, A, B, C or D, with an X designation for trills that were not included in the analyses due to limited frequency ranges or overloading of the original recordings (that was discovered later in the analyses).
ssize or samplesize is the number of trills that were at each frequency bin.

Lineage

Progress Code: completed

Statement: Recordings at the Aurora Turning site were made on an opportunistic basis on 1 and 8 December 1997 at 68.5699S, 77.9266E. This site was 1.55 km from the shoreline at Davis Station, eastern Antarctica. The water depth was 23m. The 2-m-thick-land-fast sea ice in the recording area had previously been broken up and refrozen following the arrival of the R.S.V. Aurora Australis during the station resupply 2 months earlier. There were at least five adult Weddell seals (two of each sex and one whose sex was unknown) using the haul-out holes. Recordings at other locations in the Vestfold Hills were made in November and December 1997. For more information, see the referenced paper. Only Trills that were had sinusoidal waveforms, were not masked by other seal calls or ice noises and were not distorted by too low a recording level were included in the analyses.

Notes

Purpose
This research examined the relative amplitudes of Weddell seal tonal trills as the frequencies (pitch) dropped from ~ 20 kHz down to ~ 40 Hz. Four frequency/amplitude patterns were identified and analyzed separately. Recordings were made from a (likely) single male close to Davis (Aurora Turning designation) and at other breeding locations in the Vestfold Hills (Davis group). For each trill, the maximum amplitudes (dB) at each frequency bin were measured relative to the highest amplitude (adjusted to a nominal 0 dB). The amplitude patterns were searched to identify frequencies that had a higher amplitude than adjacent frequencies (i.e., peaks in the amplitude in a frequency versus amplitude plot), which could indicate that resonance was occurring and preferentially amplifying some frequencies. The wavelengths of frequencies at which the amplitudes showed peaks were determined and matched to chambers in the Weddell seal airway in which resonance (tube closed at both ends) could be occurring. The lengths of the larynx and trachea matched some of the resonant frequencies. This research was published as: Moore, J., and Terhune, J.M. 2022. Resonance plays a secondary role in amplifying underwater vocalizations of Weddell seals (Leptonychotes weddellii). Mar. Mam. Sci. 38: 1508-1523. https://doi.org/10.1111/mms.12935