Filipa I. P. Samarra

Increasing abundance of bowhead whales in West Greenland

In April 2006, a dedicated survey of bowhead whales (Balaena mysticetus) was conducted on the former whaling ground in West Greenland to determine the current wintering population abundance. This effort included a double platform aerial survey design, satellite tracking of the movements of nine whales, and estimation of high-resolution surface time from 14 whales instrumented with time–depth recorders. Bowhead whales were estimated to spend an average of 24% (cv=0.03) of the time at or above 2 m depth, the maximum depth at which they can be seen on the trackline. This resulted in a fully corrected abundance estimate of 1229 (95% CI: 495–2939) bowhead whales when the availability factor was applied and sightings missed by observers were corrected. This surprisingly large population estimate is puzzling given that the change in abundance cannot be explained by a recent or rapid growth in population size. One possible explanation is that the population, which demonstrates high age and sex segregation, has recently attained a certain threshold size elsewhere, and a higher abundance of mature females appears on the winter and spring feeding ground in West Greenland. This in combination with the latest severe reduction in sea ice facilitating access to coastal areas might explain the surprising increase in bowhead whale abundance in West Greenland.

Killer whales (Orcinus orca) produce ultrasonic whistles

This study reports that killer whales, the largest dolphin, produce whistles with the highest fundamental frequencies ever reported in a delphinid. Using wide-band acoustic sampling from both animal-attached (Dtag) and remotely deployed hydrophone arrays, ultrasonic whistles were detected in three Northeast Atlantic populations but not in two Northeast Pacific populations. These results are inconsistent with analyses suggesting a correlation of maximum frequency of whistles with body size in delphinids, indicate substantial intraspecific variation in whistle production in killer whales, and highlight the importance of appropriate acoustic sampling techniques when conducting comparative analyses of sound repertoires.

Dose-response relationships for the onset of avoidance of sonar by free-ranging killer whales

Eight experimentally controlled exposures to 1-2 kHz or 6-7 kHz sonar signals were conducted with four killer whale groups. The source level and proximity of the source were increased during each exposure in order to reveal response thresholds. Detailed inspection of movements during each exposure session revealed sustained changes in speed and travel direction judged to be avoidance responses during six of eight sessions. Following methods developed for Phase-I clinical trials in human medicine, response thresholds ranging from 94 to 164 dB re 1 μPa received sound pressure level (SPL) were fitted to Bayesian dose-response functions. Thresholds did not consistently differ by sonar frequency or whether a group had previously been exposed, with a mean SPL response threshold of 142 ± 15 dB (mean ± s.d.). High levels of between- and within-individual variability were identified, indicating that thresholds depended upon other undefined contextual variables. The dose-response functions indicate that some killer whales started to avoid sonar at received SPL below thresholds assumed by the U.S. Navy. The predicted extent of habitat over which avoidance reactions occur depends upon whether whales responded to proximity or received SPL of the sonar or both, but was large enough to raise concerns about biological consequences to the whales.

Caller sex and orientation influence spectral characteristics of “two-voice” stereotyped calls produced by free-ranging killer whales

This study investigates how particular received spectral characteristics of stereotyped calls of sexually dimorphic adult killer whales may be influenced by caller sex, orientation, and range. Calls were ascribed to individuals during natural behavior using a towed beamforming array. The fundamental frequency of both high-frequency and low-frequency components did not differ consistently by sex. The ratio of peak energy within the fundamental of the high-frequency component relative to summed peak energy in the first two low-frequency component harmonics, and the number of modulation bands off the high-frequency component, were significantly greater when whales were oriented towards the array, while range and adult sex had little effect. In contrast, the ratio of peak energy in the first versus second harmonics of the low-frequency component was greater in calls produced by adult females than adult males, while orientation and range had little effect. The dispersion of energy across harmonics has been shown to relate to body size or sex in terrestrial species, but pressure effects during diving are thought to make such a signal unreliable in diving animals. The observed spectral differences by signaler sex and orientation suggest that these types of information may be transmitted acoustically by freely diving killer whales.

Pilot whales attracted to killer whale sounds: acoustically-mediated interspecific interactions in cetaceans.

In cetaceans’ communities, interactions between individuals of different species are often observed in the wild. Yet, due to methodological and technical challenges very little is known about the mediation of these interactions and their effect on cetaceans’ behavior. Killer whales (Orcinus orca) are a highly vocal species and can be both food competitors and potential predators of many other cetaceans. Thus, the interception of their vocalizations by unintended cetacean receivers may be particularly important in mediating interspecific interactions. To address this hypothesis, we conducted playbacks of killer whale vocalizations recorded during herring-feeding activity to free-ranging long-finned pilot whales (Globicephala melas). Using a multi-sensor tag, we were able to track the whales and to monitor changes of their movements and social behavior in response to the playbacks. We demonstrated that the playback of killer whale sounds to pilot whales induced a clear increase in group size and a strong attraction of the animals towards the sound source. These findings provide the first experimental evidence that the interception of heterospecific vocalizations can mediate interactions between different cetacean species in previously unrecognized ways.

Classification of large acoustic datasets using machine learning and crowdsourcing : application to whale calls

Vocal communication is a primary communication method of killer and pilot whales, and is used for transmitting a broad range of messages and information for short and long distance. The large variation in call types of these species makes it challenging to categorize them. In this study, sounds recorded by audio sensors carried by ten killer whales and eight pilot whales close to the coasts of Norway, Iceland, and the Bahamas were analyzed using computer methods and citizen scientists as part of the Whale FM project. Results show that the computer analysis automatically separated the killer whales into Icelandic and Norwegian whales, and the pilot whales were separated into Norwegian long-finned and Bahamas short-finned pilot whales, showing that at least some whales from these two locations have different acoustic repertoires that can be sensed by the computer analysis. The citizen science analysis was also able to separate the whales to locations by their sounds, but the separation was somewhat less accurate compared to the computer method.

A multilevel society of herring-eating killer whales indicates adaptation to prey characteristics

Lay Summary Killer whale social structure has been thought to be prey-type (fish vs. marine mammal) specific. We show that the Icelandic population, which feeds on herring, presents a multilevel society with no clear hierarchical stratification nor coherent social groups. This differs from other populations, suggesting that local ecological characteristics such as traits of the target prey and employed foraging strategy may be important drivers in shaping the social structure of the species.

Cultural evolution of killer whale calls: background, mechanisms and consequences

Cultural evolution is a powerful process shaping behavioural phenotypes of many species including our own. Killer whales are one of the species with relatively well-studied vocal culture. Pods have distinct dialects comprising a mix of unique and shared call types; calves adopt the call repertoire of their matriline through social learning. We review different aspects of killer whale acoustic communication to provide insights into the cultural transmission and gene-culture co- evolution processes that produce the extreme diversity of group and population repertoires. We argue that the cultural evolution of killer whale calls is not a random process driven by steady error accumulation alone: temporal change occurs at different speeds in different components of killer whale repertoires, and constraints in call structure and horizontal transmission often degrade the phylogenetic signal. We discuss the implications from bird song and human linguistic studies, and propose several hypotheses of killer whale dialect evolution.

North Atlantic killer whale research; past, present and future

Studying wide-ranging top predators requires a multidisciplinary and transnational approach to efficiently identify population structure, movement patterns, ecology and population parameters for effective monitoring and conservation of the populations. A recent workshop was held at the European Cetacean Society Conference, Galway Ireland, on 25 March 2012, on one of the most wide-ranging of top predators in the North Atlantic, the killer whale Orcinus orca. The workshop had as its main aims, to summarize the current state of knowledge, strengthen cooperation by evaluating the potential to share data and combine field efforts, and discuss the advances to date and future priorities for killer whale research in the North Atlantic. A selection of the presentations from this workshop is included within this special section as well as other contributions that contain relevant information on the status of killer whale research in this broad geographical area. In this Foreword, whilst not attempting to thoroughly review all published work to date, we look back at progress made on understanding the ecology and biology of North Atlantic killer whales, and based on the discussions held at the workshop suggest pressing research questions for the future, in particular highlighting how new methodologies can build upon existing work.

Identifying Variations in Baseline Behavior of Killer Whales ( Orcinus orca ) to Contextualize Their Responses to Anthropogenic Noise

Determining the baseline behavior of a whale requires understanding natural variations occurring due to environmental context, such as changes in prey behavior. Killer whales feeding on herring consistently encircle herring schools; however, depth of feeding differs from near the surface in winter to deeper than 10 m in spring and summer. These variations in feeding depth are probably due to the depth of the prey and the balance between the costs and benefits of bringing schools of herring to the surface. Such variation in baseline behavior may incur different energetic costs and consequently change the motivation of whales to avoid a feeding area. Here, we discuss these variations in feeding behavior in the context of exposure to noise and interpret observed responses to simulated navy sonar signals.