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Aerial Vocalizations by Wild and Rehabilitating Mediterranean Monk Seals (Monachus monachus) in Greece
Abstract: It is important that all aspects of the life history and behavior of Mediterranean monk seals (Monachus monachus) are documented to ensure effective management and conservation of this critically endangered species. Little is known about either airborne or underwater vocalizations for this species. Field research and rehabilitation of Mediterranean monk seal pups by MOm (MOm/Hellenic Society for the Study and Protection of the Monk Seal) provided opportunistic video recordings of the airborne sounds of this species. This study is the first to report acoustic features of airborne vocalizations from eight wild adult females and six of their pups, short-term recordings of a sick pup, and longer-term recordings of three rehabilitating pups. Although sample sizes are small, every effort was made to garner the most acoustic information from these recordings. The aims of this study were to document the acoustic properties and types of aerial vocalizations from wild and rehabilitating Mediterranean monk seals and to compare the acoustic features of their sound repertoire to the airborne vocalization characteristics of other monachids.
Audio-tracks were spectrographically analyzed using six frequency and five time variables with Spectrogram software. Through examination of real-time spectrograms and audibly distinguishable characteristics, this study classified four airborne vocalization types (bark, snort, scream, and chirp) for adult females. Three aerial vocalization types (bark, gaggle, and squawk) were documented from pups. The bark was the most common vocalization type from wild and rehabilitating pups. Wild adult female Mediterranean monk seal vocalizations ranged in frequency from 438 to 3,050 Hz and consisted of 1 to 6 components within a series with a total duration from 42 to 8,171 ms. Airborne vocalization types of rehabilitating pups ranged in frequency from 269 to 1,584 Hz and consisted of 1 to 11 components within a series with a total duration from 88 to 12,006 ms.
Using Pearson’s correlation analyses, many of the frequency and time variables were highly correlated. Principle Component Analysis (PCA), using nine variables, produced a 3-factor model that explained 98.8% of the variability in the acoustic features of the whole repertoire. A more parsimonious, 3-factor PCA model, using only six variables, still explained a high percentage of variability (81.5%). These results indicated that collecting only two frequency measurements (beginning frequency and first harmonic interval) and four time measurements (number of components within a series, total duration, component duration, and the component interval) is sufficient to distinguish among species-specific vocalizations.
Results of this acoustical analysis are from a small number of Mediterranean monk seals, and further acoustic research is warranted to record adult males, and to increase the sample sizes of vocalizations from wild adult females and pups. In addition, more recordings of ill, stressed, and captive monk seals are needed. Lastly, vocalizations of wild Mediterranean monk seals should be studied at the other two main population sites (i.e., Archipelago of Madeira and Cabo Blanco region), at other times of the year, and outside of the breeding season to provide a better understanding of the overall vocal behavior of this species. The preliminary analyses presented herein hold promise that with sufficient data on acoustic features of airborne vocalizations researchers could acoustically monitor wild Mediterranean monk seals and determine their sex, pup age, and perhaps their health.
Key Words: Mediterranean monk seal, ontogeny, Monachus monachus, behavior, acoustic, monachid, Vocalization
Document Type: Research article
Page Numbers: 262-279