Patterns in the vocalizations of male harbor seals

Abstract

Comparative analyses of the roar vocalization of male harbor seals from ten sites throughout their distribution showed that vocal variation occurs at the oceanic, regional, population, and subpopulation level. Genetic barriers based on the physical distance between harbor seal populations present a likely explanation for some of the observed vocal variation. However, site-specific vocal variations were present between genetically mixed subpopulations in California. A tree-based classification analysis grouped Scottish populations together with eastern Pacific sites, rather than amongst Atlantic sites as would be expected if variation was based purely on genetics. Lastly, within the classification tree no individual vocal parameter was consistently responsible for consecutive splits between geographic sites. Combined, these factors suggest that site-specific variation influences the development of vocal structure in harbor seals and these factors may provide evidence for the occurrence of vocal dialects.

Geographic variation and acoustic structure of the underwater vocalization of harbor seal (Phoca vitulina) in Norway, Sweden and Scotland

“…6͒. These sound types have, to our knowledge, not been documented in other harbor seal colonies that have been fairly well studied ͑Hanggi and Schusterman 1994; Van Parijs et al, 1999, 2000a, 2003Hayes et al, 2004͒. Tonal introductory phrases were characteristic for seals from Sandøy in Møre, Kongsfjord in Finnmark and Eynhallow at the Orkney Islands ͑Table II͒.…”

“…As vocalizations from more colonies are compared, useful variables for exploring variability in harbor seal vocalizations may change. However, a time-varying contour will probably be more universal ͑but see Van Parijs et al, 2003͒. The technique used to ''align'' the contours in this study assumes a high level of temporal consistency, e.g., if vocalization length increases, the length of each part must increase correspondingly. This was the case for most of the harbor seal vocalizations.…”

“…However, there are several other possible explanations for the observed vocal variation between the colonies. The harbor seal vocalizations are likely acquired through imitation and learning ͑Ralls et al., 1985;Van Parijs et al, 2003; see the review in Janik and Slater, 1997͒, and thus are primarily passed from generation to generation by cultural, rather than genetic, transmission ͑Ford, 1991͒. Once a transient seal is recruited to a colony, it may show enough social plasticity to learn the local roar.…”

“…The best-known harbor seal vocalization is a broadband, nonharmonic roar with energy in the frequency range between 50 and 4000 Hz. The roar is the only harbor seal vocalization that is reported from all studied areas, i.e., USA ͑Hanggi and Schusterman, 1994; Hayes et al, 2004͒, Norway ͑Bjørge et al, 1995͒, Sweden ͑Wahlberg et al, 2002͒, Scotland, U.K. ͑Van Parijs et al, 1997, 2000a͒, and Canada ͑Van Parijs et al, 20022003͒. The function of the roar vocalization appears primarily to be advertising the presence of a male in breeding condition, and has therefore been suggested to be used in male-male competition and/or as reproductive advertisement display to attract females ͑Hanggi and Schusterman, 1994;Van Parijs et al, 1997, 2000a, 2000bHayes et al, 2004͒.…”

“…Similar sexual display behavior is observed in other male pinnipeds such as walruses ͑Odo-benus rosmarus͒ ͑Ray and Watkins, 1975;Stirling et al, 1983, bearded seals ͑Erignathus barbatus͒ ͑Ray et al, 1969;Cleator et al, 1989͒, and Weddell seals ͑Leptonycho-tes weddelli͒ ͑Thomas and Kuechle, 1982; Thomas and Stirling, 1983͒ seals. Recent research has shown that vocal variation in harbor seal roars occurs at the oceanic, regional, population, and subpopulation level ͑Van Parijs et al, 1999, as well as individual variation in temporal ͑Van Parijs et al, 2000a͒ andspectral features ͑Hanggi andSchusterman, 1994;Van Parijs et al, 2000a͒. Factors that appear to have been important in the development of vocal geographic differences in harbor seals and other pinnipeds ͑Thomas and Thomas et al, 1988;Cleator et al, 1989;Terhune, 1994;Van Parijs et al, 2000a;2003͒ includes: ͑1͒ long distances between recording sites; ͑2͒ a strong fidelity to specific breeding sites; ͑3͒ vocal learning; ͑4͒ a polygynous mating system; ͑5͒ different acoustic transmission properties; and ͑6͒ adoptions to various environmental challenges that influence male mating strategy.…”