Frank Thomsen

Stability and group specificity of stereotyped whistles in resident killer whales, Orcinus orca, off British Columbia

Resident killer whales off British Columbia form four acoustically distinct clans, each with a unique dialect of discrete pulsed calls. Three clans belong to the northern and one to the southern community. Resident killer whales also produce tonal whistles, which play an important role in close-range communication within the northern community. However, there has been no comparative analysis of repertoires of whistles across clans. We investigated the structural characteristics, stability and group specificity of whistles in resident killer whales off British Columbia. Acoustic recordings and behavioural observations were made between 1978 and 2003. Whistles were classified spectrographically and additional observers were used to confirm our classification. Whistles were compared across clans using discriminant function analysis. We found 11 types of stereotyped whistles in the northern and four in the southern community with some of the whistle types being stable over at least 13 years. In northern residents, 10 of the 11 whistle types were structurally identical in two of the three acoustic clans, whereas the whistle types of southern residents differed clearly from those of the northern residents. Our study shows that killer whales that have no overlap in their call repertoire use essentially the same set of stereotyped whistles. Shared stereotyped whistles might provide a community-level means of recognition that facilitates association and affiliation of members of different clans, which otherwise use distinct signals. We further suggest that vocal learning between groups plays an important role in the transmission of whistle types.

Characteristics of whistles from the acoustic repertoire of resident killer whales (Orcinus orca) off Vancouver Island, British Columbia

The acoustic repertoire of killer whales (Orcinus orca) consists of pulsed calls and tonal sounds, called whistles. Although previous studies gave information on whistle parameters, no study has presented a detailed quantitative characterization of whistles from wild killer whales. Thus an interpretation of possible functions of whistles in killer whale underwater communication has been impossible so far. In this study acoustic parameters of whistles from groups of individually known killer whales were measured. Observations in the field indicate that whistles are close-range signals. The majority of whistles (90%) were tones with several harmonics with the main energy concentrated in the fundamental. The remainder were tones with enhanced second or higher harmonics and tones without harmonics. Whistles had an average bandwidth of 4.5 kHz, an average dominant frequency of 8.3 kHz, and an average duration of 1.8 s. The number of frequency modulations per whistle ranged between 0 and 71. The study indicates that whistles in wild killer whales serve a different function than whistles of other delphinids. Their structure makes whistles of killer whales suitable to function as close-range motivational sounds.

On the communicative significance of whistles in wild killer whales (Orcinus orca)

Abstract. Killer whales (Orcinus orca) use pulsed calls and whistles in underwater communication. Unlike pulsed calls, whistles have received little study and thus their function is poorly known. In this study, whistle activities of groups of individually known killer whales were compared quantitatively across behavioural categories. Acoustic recordings and simultaneous behavioural observations were made of northern resident killer whales off Vancouver Island in 1996 and 1997. Whistles were produced at greater rates than discrete calls during close-range behavioural activities than during long-range activities. They were the predominant sound-type recorded during socializing. The number of whistles per animal per minute was significantly higher during close-range behavioural activities than during long-range activities. Evidently, whistles play an important role in the close-range acoustic communication in northern resident killer whales.

On the performance of automated porpoise-click-detectors in experiments with captive harbor porpoises (Phocoena phocoena)

Recently, automated porpoise-click-detectors (T-PODs, Chelonia-Marine-Research) have been used intensively in monitoring harbor porpoises (Phocoena phocoena) in the wild. However, the automated click-detection-mechanism of the T-POD leads to questions on the characteristics of the detection process. We undertook experiments with six captive harbor porpoises (four subadult males in one pool, two adult males in another) at the Dolfinarium Harderwijk (Netherlands). One T-POD was placed for over a week in each pool, while the behavior of the porpoises was logged by visual observation. Data were analyzed using the T-POD software. A total of 725 431 clicks in 30 090 trains were recorded with 32% of the trains classified as CET HI, 27% as CET LO, and 41% as DOUBTFUL. All three train classes differed significantly in all parameters, except for click duration. We conclude that T-PODs perform generally well in detecting click trains of harbor porpoises but that in any future study trains classified as being of lower probability should be investigated very carefully to avoid the risk of losing valuable information.

Anthropogenic Noise and Conservation

Anthropogenic noise is a common but evolutionarily recent influence on communicating animals and evidence is accumulating of its adverse impacts on human health, therefore it has potential relevance to conservation. However, demonstrating that this potential is realised is not straightforward. A particular issue is the difficulty of assessing likely impacts from the limited evidence on the main factors influencing impacts—from the hearing abilities of animals of conservation concern through to the characteristics of emitted sound fields in natural environments. Further issues include the likely underestimation of behavioural effects, and a lack of knowledge of how animals trade off costs and benefits. In this chapter, we aim to highlight the main themes emerging from the growing interest in the effects of anthropogenic noise on conservation. We predominantly consider the marine environment (with examples drawn mainly from marine mammals) and the terrestrial environment (with bird examples). An important consideration that emerges from the increasing levels of anthropogenic noise and difficulties in assessing specific impacts is the need to develop interim guidance, while more detailed information is gathered and assessed.

Structural and temporal emission patterns of variable pulsed calls in free-ranging killer whales ( Orcinus orca )

Resident killer whales off Vancouver Island, British Columbia, produce variable burst pulsedcalls most commonly during close-range interactions such as socialising or social-travelling. Earlier studies indicated that variable calls are graded and can be arranged into a scale from low-frequency calls to high-frequency ones. These graded calls are often emitted in sequences, were call-classes of similar frequency follow one another more often than different classes. However, a detailed analysis of sequences was lacking to date. Therefore, our understanding of the function of variable calls during interactions among killer whales is rather limited. Simultaneous recordings of underwater vocalizations and behavioural observations from resident killer whales were collected off Vancouver Island, British Columbia during1996-2001. Socialising activities were divided into four categories: male-female, male-male, female-juvenile and juvenile-juvenile. Variable call sequences were analysed with RTS and SIGNAL acoustic-software. We found no positive correlation between group-size and number of used calls or the duration of sequences, indicating that only one or a few animals were involved in the production of each sequence. Furthermore, sequences were present in all four behaviour categories and the composition of the group had no influence on the duration of calls and used call-classes. One particular call class (V4) could be further separated into structurally distinct sub-classes. These sub-classes often formed rather stereotyped sequences. The results of our study indicate that sequences of variable calls emit broad motivational information that is not age or sex-related. Sequences of distinct sub-classes might encode more subtle information on emotional states during socialising. Therefore, variable calls might posses different functions, depending on the nature of the interaction. Thus, variable calls might be of great importance for close-range communication in wild killer whales.

Cetacean Stock Assessments in Relation to Exploration and Production Industry Activity and Other Human Pressures: Review and Data Needs

The impacts of manmade underwater sound on cetaceans have become an important environmental issue. A number of studies have documented effects on individuals such as behavioural response; masking of biologically relevant signals; and hearing loss, either temporary or permanent (reviews by Richardson et al., 1995; Southall et al., 2007). Little is known, however, about the population-level consequences of acoustic impacts. Methodologies addressing this issue, such as risk-based and cumulative impact assessments, are still in their infancy (e.g., National Research Council [NRC], 2005; Boyd et al., 2008; Wright, 2009). There is also limited information on levels of human activities generating sound and uncertainties in cetacean stock assessments that hamper quantitative investigations. Yet, sound generating industries are active in many parts of the world’s oceans and, therefore, qualitative assessments could provide a first step in managing potential conflicts between industry sectors generating sound and cetacean conservation. The Exploration and Production industry (E&P industry) generates underwater sound potentially affecting individual cetaceans, with most concerns expressed about the effects of seismic surveys (review by OSPAR, 2009). However, the relationship between E&P industry activities and trends in cetacean stocks has rarely been investigated. We provide a global overview of E&P industries and cetacean stock data in order to identify hot spots for more detailed investigations. Thus, in four case studies, we quantified the E&P industry activity in a specific region, investigated the status and trends of seven cetacean stocks therein, and assessed other factors presumably influencing the populations in question.

Behavioral reactions of cod and sole to playback of pile driving sound.

The effect of anthropogenic underwater sound on fish has become an important environmental issue. Pile‐driving noise during construction is of particular concern as the very high sound pressure levels could potentially prevent fish from reaching breeding or spawning sites, finding food, and acoustically locating mates. This could result in long‐term effects on reproduction and populationparameters. Additionally, avoidance reactions might result in displacement away from potential fishing grounds and lead to reduced catches. However, reaction thresholds and therefore the impacts of pile driving on the behavior of fish are completely unknown. Pile‐driving noise was played back to cod and sole held in two large (40 m) net pens located in a quiet bay. Movements of the fish were analyzed using a novel acoustic tracking system. Received sound pressure level and particle motion were measured during the experiments. The results show significant movement responses to the pile‐driving stimulus in both species at re...