01993nas a2200145 4500008004100000245011600041210006900157520145700226100002601683700002001709700002001729700002401749700002301773856005101796 2019 eng d00aHigh-amplitude vocalizations of male northern elephant seals and associated ambient noise on a breeding rookery0 aHighamplitude vocalizations of male northern elephant seals and 3 a

Northern elephant seals (Mirounga angustirostris) are massive, land-breeding marine mammals that produce loud, stereotyped calls during annual breeding seasons. To determine vocalization source levels emitted by competing males on a mainland breeding rookery, aerial calls were measured on-axis at 1 m from adult males using three different sound pressure level metrics. Time-averaged (1 min) ambient noise was also measured under variable environmental and social conditions. Results indicate that male northern elephant seals emit high amplitude airborne calls with little variation in call amplitude. Mean source levels ranged from 98 to 114 dB re: 20 μPa [root-mean-square (rms) -fast], 102–116 dB re: 20 μPa (rms-impulse), and 120–131 dB re: 20 μPa (peak) and average standard deviations for all metrics were <2.3 dB. Further, these seal rookeries exhibit high variability in ambient noise (in terms of both spectrum and amplitude) from biotic and environmental sources. Finally, males sampled did not adjust call amplitude to compensate for higher background noise levels and thus did not exhibit a Lombard effect. These findings reinforce the view that the remarkable vocalizations of male northern elephant seals serve as rigid and powerful signals that convey individual identity within noisy breeding colonies rather than as honest indicators of size, status, or motivation.

1 aSouthall, Brandon, L.1 aCasey, Caroline1 aHolt, Marla, M.1 aInsley, Stephen, J.1 aReichmuth, Colleen uhttp://asa.scitation.org/doi/10.1121/1.513942202525nas a2200157 4500008004100000022001300041245008300054210006900137260001600206300001100222490000700233520200800240100002802248700002602276856006502302 1962 eng d a0003347200aThe role of vocalization in the social behaviour of the northern elephant seal0 arole of vocalization in the social behaviour of the northern ele cJan-01-1962 a7 - 140 v103 a

The northern elephant seal breeds on islands off the coast of Mexico and California. It is a highly vocal species and during the breeding season vocalization plays an important role in the maintenance of the species' highly polygynous social organization. The importance of vocalization in this species is demonstrated by the presence in the adult male of a highly modified proboscis which appears to have no function other than the production of vocal threats.

Observation of colour-marked individuals on San Nicolas Island, California, showed that females of a harem tend to remain in a given spot. Females of low dominance are often forced to move by the aggressive behaviour of more dominant females and their pups are likely to become lost and to be bitten by other females. The voice of the pup attracts the mother and stimulates the mother to suckle the pup.

Observations in the field combined with spectrographic analysis of tape recordings reveal two main communicational and structural classes of vocalization, attraction calls and threat sounds. Attraction sounds (mother to pup) are unpulsed, of high and variable pitch, and show clear harmonic structure. Threat sounds (both female and male) have an opposite type of structure; they are highly pulsed, of low and steady pitch, are harsh, and lack clearcut harmonics. In general, pulse interval in the threat sounds tends to increase with body size. Among males, the resonance and volume of the clap-threat increases with the size and development of the proboscis.

Hissing occurs in many tetrapods and probably preceded and facilitated the evolution of vocal cords and patterned sounds; in turn the extensive use of different sounds as a means of communication probably facilitated the evolution of social life in the vertebrates. It is of interest that yearlings use the hiss as a threat and some yearling threat sounds are structurally intermediate between a hiss and the common roaring type of threat.

1 aBartholomew, George, A.1 aCollias, Nicholas, E. uhttp://linkinghub.elsevier.com/retrieve/pii/0003347262901240