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|Geographic variation in killer whale attacks on humpback whales in the North Pacific: implications for predation pressure
Author(s): Steiger, Gretchen H. (email@example.com); Calambokidis, John; Straley, Janice M.; Herman, Louis M.; Cerchio, Salvatore; Salden, Dan R.; Urban-R, Jorge; Jacobsen, Jeff K.; von Ziegesar, Olga; Balcomb, Kenneth C.; Gabriele, Christine M.; Dahlheim, Marilyn E.; Uchida, Senzo; Ford, John K. B.; de Guevara-P, Paloma Ladron; Yamaguchi, Manami; Barlow, Jay
Source: Endangered Species Research Volume: 4 Issue: 3 Pages: 247-256 Published: 2008
Abstract: We examined the incidence of rake mark scars from killer whales Orcinus orca on the flukes of humpback whales Megaptera novaeangliae throughout the North Pacific to assess geographic variation in predation pressure. We used 3650 identification photographs from 16 wintering or feeding areas collected during 1990 to 1993 to determine conservative estimates in the percentage of whales with rake mark scarring. Dramatic differences were seen in the incidence of rake marks among regions, with highest rates on wintering grounds off Mexico (26 vs. 14 % at others) and feeding areas off California (20 vs. 6 % at others), 2 areas between which humpback whales migrate. Although attacks are rarely witnessed, the prevalence of scars demonstrates that a substantial portion of animals are attacked, particularly those that migrate between California and Mexico. Our data also suggest that most attacks occur at or near the wintering grounds in the eastern North Pacific. The prevalence of attacks indicates that killer whale predation has the potential to be a major cause of mortality and a driving force in migratory behavior; however, the location of the attacks is inconsistent with the hypothesis that animals migrate to tropical waters to avoid predation. Our conclusion is that, at least in recent decades, attacks are made primarily on calves at the wintering grounds; this contradicts the hypothesis that killer whales historically preyed heavily on large whales in high-latitude feeding areas in the North Pacific.
A false killer whale adjusts its hearing when it echolocates
Author(s): Nachtigall, Paul E. (firstname.lastname@example.org); Supin, Alexander Y.
Source: Journal of Experimental Biology Volume: 211 Issue: 11 Pages: 1714-1718 Published: JUN 1 2008
Abstract: The use of auditory evoked potential (AEP) measurements has added considerably to knowledge of the hearing mechanisms of marine mammals. We have recently measured the hearing of a stranded infant Risso's dolphin, the audiograms of white-beaked dolphins temporarily caught and released, and the hearing of anaesthetized polar bears. Most small toothed whales echolocate and hear very high frequency sounds underwater. While much has previously been learned about the echolocation performance and characteristics of the outgoing signals of echolocating dolphins and small whales, the hearing processes occurring while these animals actively echolocate have not previously been examined. Working with a well-trained echolocating false killer whale (Pseudorca crassidens) wearing latex surface suction cup electrodes, we have measured echolocation hearing AEPs in response to outgoing echolocation clicks, returning echoes, and comparable simulated whale clicks and echoes in a variety of situations. We have found that: (1) the whale may hear her loud outgoing clicks and much quieter returning echoes at comparable levels, (2) the whale has protective mechanisms that dampen the intensity of her outgoing signals-she hears her outgoing signals at a level about 40 dB lower than similar signals presented directly in front of her, (3) when echo return levels are lowered either by making the targets smaller or by placing the targets farther away-without changing the levels of her outgoing signals-the hearing of these echoes remains at almost the same level, (4) if targets are made much smaller and harder to echolocate, the animal will modify what she hears of her outgoing signal-as if to heighten overall hearing sensitivity to keep the echo level hearable, (5) the animal has an active automatic gain control' mechanism in her hearing based on both forward masking that balances outgoing pulse intensity and time between pulse and echo, and active hearing control. Overall, hearing during echolocation appears to be a very active process.
Temporal and contextual patterns of killer whale (Orcinus orca) call type production
Author(s): Foote, Andrew D. (email@example.com); Osborne, Richard W.; Hoelzel, A. Rus
Source: Ethology Volume: 114 Issue: 6 Pages: 599-606 Published: JUN 2008
Abstract: Fish-eating killer whales Orcinus orca in the northeastern Pacific live in highly stable matrifocal social groups called pods. Each pod produces a repertoire of seven or more stereotyped call types. We compared the relative production of call types of free-ranging killer whale pods over time and between social contexts. The relative production of call types by each pod during directional travel was distinct over a 27-yr period; however, both temporal stability and pod distinctiveness were strongly influenced by a subset of dominant call types within the repertoire of each pod. Some call types within the repertoires contain biphonation (two overlapping independently modulated tones) and have a higher estimated active space than call types containing just one tone. In multi-pod aggregations the relative production of the dominant call types of each pod decreased and the relative production of a subset of call types that are rarely recorded from single-pod groupings increased. The majority of these contained biphonation. The data suggest a distinction between a subset of dominant call types that may function to identify the pod and a subset of less common call types including several call types containing biphonation that are more commonly produced during inter-pod affiliations.
Variation in call pitch among killer whale ecotypes
Author(s): Foote, Andrew D. (firstname.lastname@example.org); Nystuen, Jeffrey A.
Source: Journal of the Acoustical Society of America Volume: 123 Issue: 3 Pages: 1747-1752 Published: MAR 2008
Abstract: Vocal structure can vary between populations due to variation in ecology-dependent selection pressures, such as masking by background noise and the presence of eavesdroppers. Signalers can overcome these obstacles to effective communication by avoiding frequencies that overlap with background noise or the audible range of eavesdroppers. In the Northeastern Pacific three "ecotypes" of killer whale coexist in sympatry, but differ from one another in their diet and habitat use. The minimum frequency (F-min) and the frequency containing the peak energy between 0 and 10 kHz (F-peak) of a random sample of calls produced by a population of each ecotype was measured. The offshore ecotype produced calls with a significantly higher F-min than the other ecotypes, which could be a strategy to avoid masking by low frequency chronic bandlimited wind noise found in the offshore environment. The resident ecotype produced calls with a significantly higher F-min and F-peak than the transient ecotype. This could be to reduce detection by their salmonid prey, which has a narrow band, low frequency auditory range. (C) 2008 Acoustical Society of America.
Intra- and intergroup vocal behavior in resident killer whales, Orcinus orca
Author(s): Weib, Brigitte M. (email@example.com); Symonds, Helena; Spong, Paul; Ladich, Friedrich (Friedrich.Ladich@univie.ac.at)
Source: Journal of the Acoustical Society of America Volume: 122 Issue: 6 Pages: 3710-3716 Published: DEC 2007
Abstract: Vocal communication within and between groups of individuals has been described extensively in birds and terrestrial mammals, however, little is known about how cetaceans utilize their sounds in their natural environment. Resident killer whales, Orcinus orca, live in highly stable matrilines and exhibit group-specific vocal dialects. Single call types cannot exclusively be associated with particular behaviors and calls are thought to function in group identification and intragroup communication. In the present study call usage of three closely related matrilines of the Northern resident community was compared in various intra- and intergroup contexts. In two out of the three matrilines significant changes in vocal behavior depending both on the presence and identity of accompanying whales were found. Most evidently, family-specific call subtypes, as well as aberrant and variable calls, were emitted at higher rates, whereas "low arousal" call types were used less in the presence of matrilines from different pods, subclans, or clans. Ways in which the observed changes may function both in intra- and intergroup communication. (c) 2007 Acoustical Society of America.
Automatic classification of killer whale vocalizations using dynamic time warping
Author(s): Brown, Judith C. (firstname.lastname@example.org); Miller, Patrick J. O. (email@example.com)
Source: Journal of the Acoustical Society of America Volume: 122 Issue: 2 Pages: 1201-1207 Published: AUG 2007
Abstract: A set of killer Whale sounds from Marineland were recently classified automatically [Brown et al., J. Acoust. Soc. Am. 119, EL34-EL40 (2006)] into call types using dynamic time warping (DTW), multidimensional scaling, and kmeans clustering to give near-perfect agreement with a perceptual classification. Here the effectiveness of four DTW algorithms on a larger and much more challenging set of calls by Northern Resident whales will be examined, with each call consisting of two independently modulated pitch contours and having considerable overlap in contours for several of the perceptual call types. Classification results are given for each of the four algorithms for the, low frequency contour (LFC), the high frequency contour (HFC), their derivatives, and weighted sums of the distances corresponding to LFC with HFC, LFC with its derivative, and HFC with its derivative. The best agreement with the perceptual classification was 90% attained by the Sakoe-Chiba algorithm for the low frequency contours alone. (C) 2007 Acoustical Society of America.
Predation by killer whales (Orcinus orca) and the evolution of whistle loss and narrow-band high frequency clicks in odontocetes
Author(s): Morisaka, T. (firstname.lastname@example.org); Connor, R. C.
Source: Journal of Evolutionary Biology Volume: 20 Issue: 4 Pages: 1439-1458 Published: JUL 2007
Abstract: A disparate selection of toothed whales (Odontoceti) share striking features of their acoustic repertoires including the absence of whistles and high frequency but weak (low peak-to-peak source level) clicks that have a relatively long duration and a narrow bandwidth. The non-whistling, high frequency click species include members of the family Phocoenidae, members of one genus of delphinids, Cephalorhynchus, the pygmy sperm whale, Kogia breviceps, and apparently the sole member of the family Pontoporiidae. Our review supports the 'acoustic crypsis' hypothesis that killer whale predation risk was the primary selective factor favouring an echolocation and communication system in cephalorhynchids, phocoenids and possibly Pontoporiidae and Kogiidae restricted to sounds that killer whales hear poorly or not at all (<2> 100 kHz).
Caller sex and orientation influence spectral characteristics of "two-voice" stereotyped calls produced by free-ranging killer whales
Author(s): Miller, Patrick J. O. (email@example.com); Samarra, Filipa I. P.; Perthuison, Aurelie D.
Source: Journal of the Acoustical Society of America Volume: 121 Issue: 6 Pages: 3932-3937 Published: JUN 2007
Abstract: 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 suguest that these types of information may be transmitted acoustically by freely diving killer whales. (c) 2007 Acoustical Society of America.
Echolocation clicks from killer whales (Orcinus orca) feeding on herring (Clupea harengus) (L)
Author(s): Simon, Malene (firstname.lastname@example.org); Wahlberg, Magnus; Miller, Lee A.
Source: Journal of the Acoustical Society of America Volume: 121 Issue: 2 Pages: 749-752 Published: FEB 2007
Abstract: Echolocation clicks from Norwegian killer whales feeding on herring schools were recorded using a four-hydrophone array. The clicks had broadband bimodal frequency spectra with low and high frequency peaks at 24 and 108 kHz, respectively. The -10 dB bandwidth was 35 kHz. The average source level varied from 173 to 202 dB re 1 mu Pa (peak-to-peak) @ 1 m. This is considerably lower than source levels described for Canadian killer whales foraging on salmon. It is suggested that biosonar clicks of Norwegian killer whales are adapted for localization of prey with high target strength and acute hearing abilities. (c) 2007 Acoustical Society of America.