Passive acoustic surveys were conducted to assess the vocal behavior of North Atlantic right whales (Eubalaena glacialis) in the designated critical calving habitat along the shallow coastal waters of southeastern United States. Underwater vocalizations were recorded using autonomous buoys deployed in close proximity to surface active groups (SAGs). Nine main vocalization types were identified with manual inspection of spectrograms, and standard acoustic descriptors were extracted. Classification trees were used to examine the distinguishing characteristics of calls and quantify their variability within the SAG vocal repertoire. The results show that descriptors of frequency, bandwidth, and spectral disorder are the most important parameters for partitioning the SAG repertoire, contrary to duration-related measures. The reported source levels and vocalization statistics provide sound production data vital to inform regional passive acoustic monitoring and conservation for this endangered species.

North Atlantic right whales (Eubalaena glacialis) produce loud, broadband, short duration sounds referred to as gunshots. The sounds have been hypothesized to function in a reproductive context, as sexual advertisement signals produced by solitary adult males to attract females and/or agonistic displays among males in surface active groups. This study provides evidence that gunshot sounds are also produced by adult females and examines the acoustics and behavioral contexts associated with these calls. Results from boat-based observational surveys investigating the early vocal ontogeny and behavior of right whales in the critical southeast calving habitat are presented for a subset of mothers who produced gunshots while in close proximity to their calves. Of 26 different isolated mother-calf pairs, gunshots were recorded from females of varied ages and maternal experience. The signals were recorded when calves separated from their mothers during curious approaches toward objects on the surface. While the spectral and temporal characteristics of female gunshots resemble those attributed to adult males, these calls were orders of magnitude quieter (Ő30 dB). Relatively quiet gunshots posed minimal risk of injury to nearby calves. The social and behavioral context suggests gunshots were associated with maternal communication and may also be indicators of stress and agitation.

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There is mention of single-ear fusion, interaural fusion time, ordinary delay time, etc. All these have to be fitted to some theory, and Mr. Brittain has assisted us in this. However, at one stage he mentions the de Haas effect as an explanation for the breakdown of one of the systems. Any theory of inter-aural fusion must first explain this effect.The de Haas effect shows that, when two identical signals are presented to two loudspeakers which are identical, a person in the middle hears a sound image in the middle until he moves his head slightly to that side, when the sound image immediately rushes to one side, even though the delays involved in less than a few inches' change of the head are still all within about 0-5 millisec.Mr. G. M. E. Williams: The quality of reproduction has not been mentioned, and I would like to have Mr. Somerville's views on the subject, because this question is worrying some workers in this field in the United States. They believe that the quality of reproduction on stereophonic discs must necessarily be poorer than on monophonic discs.The second point is addressed to Mr. Brittain. I am not clear whether the discrimination of the difference in time between the two ears occurs between the ears and the brain or in the brain. If it occurs in the brain, is it possible to provide people who are deaf in one ear with a binaural effect by providing them with a microphone attached to the defective ear and a reproducer in the effective ear which enables them not only to hear the sound directly but also to hear the sound via the microphone from the other side of the head ?There seems to be confusion about the aim in providing stereophonic reproduction. In one of his slides, Mr. Brittain showed six sources, and an observer in one position stated that the images were 'bunched'. The images are likely to appear 'bunched' for anybody in the hall unless he is on the centre Linenamely the geometric line of symmetry of the arrangement of microphones. In most halls that is usually the gangway, and so it is not very practical. Mr. Somerville's definitions, particularly of 'sound stage' instead of 'sound field' take on a new significance in view of the disclosures in the papers. It seems clear that the ears cannot be persuaded as effectively as the eyes by stereophotography. The eyes possess sharp focusing and directive powers which the ears do not have. It therefore seems inevitable that a major effort is required to determine the nature and limits of what is worth presenting to the ears to give a sense of direction to artificial sources of sound. This question may have to be resolved subjectively.Mr. H. A. M. Clark: Mr. Somerville raised an important point which I should like to emphasize, namely that, although directional information in the low-frequency region is not of prime importance, from the point of view of reproducing goodqualitv sound it is exceedingly important. I was very pleased to have confirmation of my opinion that one of the reasons why it is so important is because the tone quality of a...