Publications

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2018
Varga, LM, Wiggins SM, Hildebrand JA.  2018.  Behavior of singing fin whales Balaenoptera physalus tracked acoustically offshore of Southern California. Endangered Species Research. 35:113-124.   10.3354/esr00881   AbstractWebsite

Fin whales Balaenoptera physalus produce stereotyped low-frequency calls (1530 Hz) that can be detected at great ranges and are considered song when produced in a repeated temporal pattern. These calls, referred to as 20 Hz calls, were localized and tracked using a 1 km aperture array of 4 passive acoustic recorders at approximately 800 m depth northwest of San Clemente Island, offshore of Southern California, USA, for 4 continuous weeks during late fall 2007. A total of 1454 calls were localized over the recording period. The average (+/- SD) estimated source sound pressure level was 194.8 +/- 0.2 dB(pp) re 1 mu Pa-2 at 1 m (where pp is peak-to-peak) and 180.9 +/- 0.2 dB(rms) re 1 mu Pa at 1 m (where rms is root mean square). The majority of these calls were in the form of a doublet song pattern, with average inter-pulse intervals of 13 and 18 s. These tracks are the first to be reported for transiting solitary singing fin whales using passive acoustic monitoring techniques. Acoustic tracking of fin whales provides insight into the ecology and behavior of this endangered species as well as vocal behaviors, which are important when studying the potential impact of anthropogenic noise. Call source sound pressure level, along with calling behavior, provides important parameters required for population density estimation. Furthermore, studying fin whale song patterns may aid in distinguishing different subpopulations.

2014
Henderson, EE, Smith MH, Gassmann M, Wiggins SM, Douglas AB, Hildebrand JA.  2014.  Delphinid behavioral responses to incidental mid-frequency active sonar. Journal of the Acoustical Society of America. 136:2003-2014.   10.1121/1.4895681   AbstractWebsite

Opportunistic observations of behavioral responses by delphinids to incidental mid-frequency active (MFA) sonar were recorded in the Southern California Bight from 2004 through 2008 using visual focal follows, static hydrophones, and autonomous recorders. Sound pressure levels were calculated between 2 and 8 kHz. Surface behavioral responses were observed in 26 groups from at least three species of 46 groups out of five species encountered during MFA sonar incidents. Responses included changes in behavioral state or direction of travel, changes in vocalization rates and call intensity, or a lack of vocalizations while MFA sonar occurred. However, 46% of focal groups not exposed to sonar also changed their behavior, and 43% of focal groups exposed to sonar did not change their behavior. Mean peak sound pressure levels when a behavioral response occurred were around 122 dB re: 1 mu Pa. Acoustic localizations of dolphin groups exhibiting a response gave insight into nighttime movement patterns and provided evidence that impacts of sonar may be mediated by behavioral state. The lack of response in some cases may indicate a tolerance of or habituation to MFA sonar by local populations; however, the responses that occur at lower received levels may point to some sensitization as well. (C) 2014 Acoustical Society of America.

2013
Gassmann, M, Henderson EE, Wiggins SM, Roch MA, Hildebrand JA.  2013.  Offshore killer whale tracking using multiple hydrophone arrays. Journal of the Acoustical Society of America. 134:3513-3521.   10.1121/1.4824162   AbstractWebsite

To study delphinid near surface movements and behavior, two L-shaped hydrophone arrays and one vertical hydrophone line array were deployed at shallow depths (<125 m) from the floating instrument platform R/P FLIP, moored northwest of San Clemente Island in the Southern California Bight. A three-dimensional propagation-model based passive acoustic tracking method was developed and used to track a group of five offshore killer whales (Orcinus orca) using their emitted clicks. In addition, killer whale pulsed calls and high-frequency modulated (HFM) signals were localized using other standard techniques. Based on these tracks sound source levels for the killer whales were estimated. The peak to peak source levels for echolocation clicks vary between 170-205 dB re 1 mu Pa @ 1 m, for HFM calls between 185-193 dB re 1 mu Pa @ 1 m, and for pulsed calls between 146-158 dB re 1 mu Pa @ 1 m. (C) 2013 Acoustical Society of America.

2012
Simonis, AE, Baumann-Pickering S, Oleson E, Melcon ML, Gassmann M, Wiggins SM, Hildebrand JA.  2012.  High-frequency modulated signals of killer whales (Orcinus orca) in the North Pacific. Journal of the Acoustical Society of America. 131:EL295-EL301.   10.1121/1.3690963   AbstractWebsite

Killer whales in the North Pacific, similar to Atlantic populations, produce high-frequency modulated signals, based on acoustic recordings from ship-based hydrophone arrays and autonomous recorders at multiple locations. The median peak frequency of these signals ranged from 19.6-36.1 kHz and median duration ranged from 50-163 ms. Source levels were 185-193 dB peak-to-peak re: 1 mu Pa at 1 m. These uniform, repetitive, down-swept signals are similar to bat echolocation signals and possibly could have echolocation functionality. A large geographic range of occurrence suggests that different killer whale ecotypes may utilize these signals. (C) 2012 Acoustical Society of America

2010
Baumann-Pickering, S, Wiggins SM, Hildebrand JA, Roch MA, Schnitzler HU.  2010.  Discriminating features of echolocation clicks of melon-headed whales (Peponocephala electra), bottlenose dolphins (Tursiops truncatus), and Gray's spinner dolphins (Stenella longirostris longirostris). Journal of the Acoustical Society of America. 128:2212-24.   10.1121/1.3479549   AbstractWebsite

Spectral parameters were used to discriminate between echolocation clicks produced by three dolphin species at Palmyra Atoll: melon-headed whales (Peponocephala electra), bottlenose dolphins (Tursiops truncatus) and Gray's spinner dolphins (Stenella longirostris longirostris). Single species acoustic behavior during daytime observations was recorded with a towed hydrophone array sampling at 192 and 480 kHz. Additionally, an autonomous, bottom moored High-frequency Acoustic Recording Package (HARP) collected acoustic data with a sampling rate of 200 kHz. Melon-headed whale echolocation clicks had the lowest peak and center frequencies, spinner dolphins had the highest frequencies and bottlenose dolphins were nested in between these two species. Frequency differences were significant. Temporal parameters were not well suited for classification. Feature differences were enhanced by reducing variability within a set of single clicks by calculating mean spectra for groups of clicks. Median peak frequencies of averaged clicks (group size 50) of melon-headed whales ranged between 24.4 and 29.7 kHz, of bottlenose dolphins between 26.7 and 36.7 kHz, and of spinner dolphins between 33.8 and 36.0 kHz. Discriminant function analysis showed the ability to correctly discriminate between 93% of melon-headed whales, 75% of spinner dolphins and 54% of bottlenose dolphins.