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McDonald, MA, Hildebrand JA, Wiggins SM, Ross D.  2008.  A 50 year comparison of ambient ocean noise near San Clemente Island: a bathymetrically complex coastal region off Southern California. Journal of the Acoustical Society of America. 124:1985-92.   10.1121/1.2967889   AbstractWebsite

Repeated ocean ambient noise measurements at a shallow water (110 m) site near San Clemente Island reveal little increase in noise levels in the absence of local ships. Navy reports document ambient noise levels at this site in 1958-1959 and 1963-1964 and a seafloor recorder documents noise during 2005-2006. When noise from local ships was excluded from the 2005-2006 recordings, median sound levels were essentially the same as were observed in 1958 and 1963. Local ship noise, however, was present in 31% of the recordings in 1963 but was present in 89% of the recordings in 2005-2006. Median levels including local ships are 6-9 dB higher than median levels chosen from times when local ship noise was absent. Biological sounds and the sound of wind driven waves controlled ambient noise levels in the absence of local ships. The median noise levels at this site are low for an open water site due to the poor acoustic propagation and low average wind speeds. The quiet nature of this site in the absence of local ships allows correlation of wind speed to wave noise across the 10-220 Hz spectral band of this study.

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Baumann-Pickering, S, Roch MA, Wiggins SM, Schnitzler HU, Hildebrand JA.  2015.  Acoustic behavior of melon-headed whales varies on a diel cycle. Behavioral Ecology and Sociobiology. 69:1553-1563.   10.1007/s00265-015-1967-0   AbstractWebsite

Many terrestrial and marine species have a diel activity pattern, and their acoustic signaling follows their current behavioral state. Whistles and echolocation clicks on long-term recordings produced by melon-headed whales (Peponocephala electra) at Palmyra Atoll indicated that these signals were used selectively during different phases of the day, strengthening the idea of nighttime foraging and daytime resting with afternoon socializing for this species. Spectral features of their echolocation clicks changed from day to night, shifting the median center frequency up. Additionally, click received levels increased with increasing ambient noise during both day and night. Ambient noise over a wide frequency band was on average higher at night. The diel adjustment of click features might be a reaction to acoustic masking caused by these nighttime sounds. Similar adaptations have been documented for numerous taxa in response to noise. Or it could be, unrelated, an increase in biosonar source levels and with it a shift in center frequency to enhance detection distances during foraging at night. Call modifications in intensity, directionality, frequency, and duration according to echolocation task are well established for bats. This finding indicates that melon-headed whales have flexibility in their acoustic behavior, and they collectively and repeatedly adapt their signals from day- to nighttime circumstances.

McDonald, MA, Hildebrand JA, Wiggins SM, Johnston DW, Polovina JJ.  2009.  An acoustic survey of beaked whales at Cross Seamount near Hawaii (L). Journal of the Acoustical Society of America. 125:624-627.   10.1121/1.3050317   AbstractWebsite

An acoustic record from Cross Seamount, southwest of Hawaii, revealed sounds characteristic of beaked whale echolocation at the same relative abundance year-around (270 of 356 days), occurring almost entirely at night. The most common sound had a linear frequency upsweep from 35 to 100 kHz (the bandwidth of recording), an interpulse interval of 0.11 s, and duration of at least 932 mu s. A less common upsweep sound with shorter interpulse interval and slower sweep rate was also present. Sounds matching Cuvier's beaked whale were not detected, and Blainville's beaked whale sounds were detected on only one occasion. (C) 2009 Acoustical Society of America. [DOI: 10.1121/1.3050317]

Bayless, AR, Oleson EM, Baumann-Pickering S, Simonis AE, Marchetti J, Martin S, Wiggins SM.  2017.  Acoustically monitoring the Hawai'i longline fishery for interactions with false killer whales. Fisheries Research. 190:122-131.   10.1016/j.fishres.2017.02.006   AbstractWebsite

False killer whales (Pseudorca crassidens) feed primarily on several species of large pelagic fish, species that are also targeted by the Hawai'i-permitted commercial deep-set longline fishery. False killer whales have been known to approach fishing lines in an attempt to procure bait or catch from the lines, a behavior known as depredation. This behavior can lead to the hooking or entanglement of an animal, which currently exceeds sustainable levels for pelagic false killer whales in Hawaii. Passive acoustic monitoring (PAM) was used to record false killer whales near longline fishing gear to investigate the timing, rate, and spatial extent of false killer whale occurrence. Acoustic data were collected using small autonomous recorders modified for deployment on the mainline of longline fishing gear. A total of 90 fishing sets were acoustically monitored in 2013 and 2014 on a chartered longline vessel using up to five acoustic recorders deployed throughout the fishing gear. Of the 102 odontocete click and/or whistle bouts detected on 55 sets, 26 bouts detected on 19 different fishing sets were classified as false killer whales with high or medium confidence based on either whistle classification, click classification, or both. The timing of false killer whale acoustic presence near the gear was related to the timing of fishing activities, with 57% of the false killer whale bouts occurring while gear was being hauled, with 50% of those bouts occurring during the first third of the haul. During three fishing sets, false killer whales were detected on more than one recorder, and in all cases the whales were recorded on instruments farther from the fishing vessel as the haul proceeded. Only three of the 19 sets with acoustically-confirmed false killer whale presence showed signs of bait or catch damage by marine mammals, which may relate to the difficulty of reporting depredation. PAM has proven to be a relatively inexpensive and efficient method for monitoring the Hawai'i longline fishery for interactions with false killer whales. (C) 2017 Elsevier B.V. All rights reserved.

Baumann-Pickering, S, Simonis AE, Wiggins SM, Brownell RL, Hildebrand JA.  2012.  Aleutian Islands beaked whale echolocation signals. Marine Mammal Science. :-no.   10.1111/j.1748-7692.2011.00550.x   AbstractWebsite

Beaked whales are an elusive group of marine mammals. They are infrequently encountered as they are pelagic, deep diving foragers with short surface intervals between long dives (Tyack et al. 2006). In recent years, research has shown that beaked whales produce frequency modulated (FM) upsweep echolocation signals (Zimmer et al. 2005, Johnson et al. 2006, Gillespie et al. 2009, McDonald et al. 2009, Baumann-Pickering et al. 2010), which appear to be species specific in their spectral and temporal characteristics. Their typical echolocation behavior during foraging consists of FM pulses with very regular interpulse intervals (IPIs) while searching for prey, and discrete click series with short IPIs when closing in on a potential prey target, called a buzz (Johnson et al. 2004, Madsen et al. 2005).

Cranford, TW, McKenna MF, Soldevilla MS, Wiggins SM, Goldbogen JA, Shadwick RE, Krysl P, St Leger JA, Hildebrand JA.  2008.  Anatomic geometry of sound transmission and reception in Cuvier's beaked whale (Ziphius cavirostris). Anatomical Record-Advances in Integrative Anatomy and Evolutionary Biology. 291:353-378.   10.1002/ar.20652   AbstractWebsite

This study uses remote imaging technology to quantify, compare, and contrast the cephalic anatomy between a neonate female and a young adult male Cuvier's beaked whale. Primary results reveal details of anatomic geometry with implications for acoustic function and diving. Specifically, we describe the juxtaposition of the large pterygoid sinuses, a fibrous venous plexus, and a lipid-rich pathway that connects the acoustic environment to the bony ear complex. We surmise that the large pterygoid air sinuses are essential adaptations for maintaining acoustic isolation and auditory acuity of the ears at depth. In the adult male, an acoustic waveguide lined with pachyosteosclerotic bones is apparently part of a novel transmission pathway for outgoing biosonar signals. Substitution of dense tissue boundaries where we normally find air sacs in delphinoids appears to be a recurring theme in deep-diving beaked whales and sperm whales. The anatomic configuration of the adult male Ziphius forehead resembles an upside-down sperm whale nose and may be its functional equivalent, but the homologous relationships between forehead structures are equivocal. Anat Rec, 291:353-378, 2008. © 2008 Wiley-Liss, Inc.

Hildebrand, JA, Frasier KE, Baumann-Pickering S, Wiggins SM, Merkens KP, Garrison LP, Soklevilla MS, McDonald MA.  2019.  Assessing seasonality and density from passive acoustic monitoring of signals presumed to be from pygmy and dwarf sperm whales in the Gulf of Mexico. Frontiers in Marine Science. 6   10.3389/fmars.2019.00066   AbstractWebsite

Pygmy sperm whales (Kogia breviceps) and dwarf sperm whales (Kogia sima) are deep diving cetaceans that commonly strand along the coast of the southeast US, but that are difficult to study visually at sea because of their elusive behavior. Conventional visual surveys are thought to significantly underestimate the presence of Kogia and they have proven difficult to approach for tracking and tagging. An approach is presented for density estimation of signals presumed to be from Kogia spp. based on passive acoustic monitoring data collected at sites in the Gulf of Mexico (GOM) from the period following the Deepwater Horizon oil spill (2010-2013). Both species of Kogia are known to inhabit the GOM, although it is not possible to acoustically separate the two based on available knowledge of their echolocation clicks. An increasing interannual density trend is suggested for animals near the primary zone of impact of the oil spill, and to the southeast of the spill. Densities were estimated based on both counting individual echolocation clicks and counting the presence of groups of animals during one-min time windows. Densities derived from acoustic monitoring at three sites are all substantially higher (4-16 animals/1000 km(2)) than those that have been derived for Kogia from line transect visual surveys in the same region (0.5 animals/1000 km(2)). The most likely explanation for the observed discrepancy is that the visual surveys are underestimating Kogia spp. density, due to the assumption of perfect detectability on the survey trackline. We present an alternative approach for density estimation, one that derives echolocation and behavioral parameters based on comparison of modeled and observed sound received levels at sites of varying depth.

Frasier, KE, Roch MA, Soldevilla MS, Wiggins SM, Garrison LP, Hildebrand JA.  2017.  Automated classification of dolphin echolocation click types from the Gulf of Mexico. Plos Computational Biology. 13   10.1371/journal.pcbi.1005823   AbstractWebsite

Delphinids produce large numbers of short duration, broadband echolocation clicks which may be useful for species classification in passive acoustic monitoring efforts. A challenge in echolocation click classification is to overcome the many sources of variability to recognize underlying patterns across many detections. An automated unsupervised network-based classification method was developed to simulate the approach a human analyst uses when categorizing click types: Clusters of similar clicks were identified by incorporating multiple click characteristics (spectral shape and inter-click interval distributions) to distinguish within-type from between-type variation, and identify distinct, persistent click types. Once click types were established, an algorithm for classifying novel detections using existing clusters was tested. The automated classification method was applied to a dataset of 52 million clicks detected across five monitoring sites over two years in the Gulf of Mexico (GOM). Seven distinct click types were identified, one of which is known to be associated with an acoustically identifiable delphinid (Risso's dolphin) and six of which are not yet identified. All types occurred at multiple monitoring locations, but the relative occurrence of types varied, particularly between continental shelf and slope locations. Automatically- identified click types from autonomous seafloor recorders without verifiable species identification were compared with clicks detected on sea-surface towed hydrophone arrays in the presence of visually identified delphinid species. These comparisons suggest potential species identities for the animals producing some echolocation click types. The network-based classification method presented here is effective for rapid, unsupervised delphinid click classification across large datasets in which the click types may not be known a priori.

Wiggins, S.  2003.  Autonomous acoustic recording packages (ARPs) for long-term monitoring of whale sounds. Marine Technology Society Journal. 37:13-22.   10.4031/002533203787537375 pp.13-22   AbstractWebsite

Advancements in low-power and high-data capacity computer technology during the past decade have been adapted to autonomously record acoustic data from vocalizing whales over long time periods. Acoustic monitoring of whales has advantages over traditional visual surveys including greater detection ranges, continuous long-term monitoring in remote locations and in various weather conditions, and lower cost. An autonomous acoustic recording package (ARP) is described that uses a tethered hydrophone above a seafloor-mounted instrument frame. ARPs have been deployed to record baleen whale sounds in the Bering Sea, off the coast of southern California, near the West Antarctic Peninsula, and near Hawaii. ARP data have provided new information on the seasonal presence, abundance, call character, and patterns of vocalizing whales. Current development is underway for a broader-band, higher-data capacity system capable of recording odontocete whales, dolphins, and porpoises for long time periods.

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Baumann-Pickering, S, M. Yack T, Barlow J, Wiggins SM, Hildebrand JA.  2013.  Baird's beaked whale echolocation signals. The Journal of the Acoustical Society of America. 133:4321-4331.   10.1121/1.4804316   AbstractWebsite

Echolocation signals from Baird's beaked whales were recorded during visual and acoustic shipboard surveys of cetaceans in the California Current ecosystem and with autonomous, long-term recorders in the Southern California Bight. The preliminary measurement of the visually validated Baird's beaked whale echolocation signals from towed array data were used as a basis for identifying Baird's signals in the autonomous recorder data. Two distinct signal types were found, one being a beaked whale-like frequency modulated (FM) pulse, the other being a dolphin-like broadband click. The median FM inter-pulse interval was 230 ms. Both signal types showed a consistent multi-peak structure in their spectra with peaks at ∼9, 16, 25, and 40 kHz. Depending on signal type, as well as recording aspect and distance to the hydrophone, these peaks varied in relative amplitude. The description of Baird's echolocation signals will allow for studies of their distribution and abundance using towed array data without associated visual sightings and from autonomous seafloor hydrophones.

Wiggins, SM, McDonald MA, Hildebrand JA.  2012.  Beaked whale and dolphin tracking using a multichannel autonomous acoustic recorder. The Journal of the Acoustical Society of America. 131:156-163.   10.1121/1.3662076   AbstractWebsite

To track highly directional echolocation clicks from odontocetes, passive hydrophone arrays with small apertures can be used to receive the same high frequency click on each sensor. A four-hydrophone small-aperture array was coupled to an autonomous acoustic recorder and used for long-term tracking of high-frequency odontocete sounds. The instrument was deployed in the spring of 2009 offshore of southern California in a known beaked whale and dolphin habitat at about 1000 m depth. The array was configured as a tetrahedron with approximately 0.5 m sensor spacing. Time difference of arrival measurements between the six sensor-pairs were used to estimate three-dimensional bearings to sources. Both near-seafloor beaked whales and near-sea surface dolphins were tracked. The tracks observed using this technique provide swimming and diving behavioral information for free-ranging animals using a single instrument. Furthermore, animal detection ranges were derived, allowing for estimation of detection probability functions. (C) 2012 Acoustical Society of America. [DOI: 10.1121/1.3662076]

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.

Sirovic, A, Hildebrand JA, Wiggins SM, Thiele D.  2009.  Blue and fin whale acoustic presence around Antarctica during 2003 and 2004. Marine Mammal Science. 25:125-136.   10.1111/j.1748-7692.2008.00239.x   AbstractWebsite

Seasonal and spatial variations of blue (Balaenoptera musculus) and fin whale (B. physalus) calls were analyzed from recordings collected with Acoustic Recording Packages (ARPs) deployed between January 2003 and July 2004 at four circumpolar locations: the Western Antarctic Peninsula (WAP), the Scotia Sea (SS), Eastern Antarctica (EA), and the Ross Sea (RS). Call characteristics were compared among sites using the average pressure spectrum levels from 1 month of data at each location. Presence of calls was analyzed using automatic call detection and acoustic power analysis methods. Blue whale calls were recorded year-round, with the highest detections in February-May and November. This suggests that the blue whale population may not migrate synchronously, and may indicate long duration calls are more common during migrations. Fin whale calls were detected only during February-July. Two distinct fin whale call types were recorded, suggesting a possible separation into two populations. The calls at the EA site had a secondary frequency peak in the pressure spectrum at 99 Hz and the calls at the WAP and the SS sites had a peak at 89 Hz. No fin whale calls were detected at the RS site. Acoustics are a good tool to monitor large whales in the Southern Ocean.

Sirovic, A, Hildebrand JA, Wiggins SM.  2007.  Blue and fin whale call source levels and propagation range in the Southern Ocean. Journal of the Acoustical Society of America. 122:1208-15.   10.1121/1.2749452   AbstractWebsite

Blue (Balaenoptera musculus) and fin whales (B. physalus) produce high-intensity, low-frequency calls, which probably function for communication during mating and feeding. The source levels of blue and fin whale calls off the Western Antarctic Peninsula were calculated using recordings made with calibrated, bottom-moored hydrophones. Blue whales were located up to a range of 200 km using hyperbolic localization and time difference of arrival. The distance to fin whales, estimated using multipath arrivals of their calls, was up to 56 km. The error in range measurements was 3.8 km using hyperbolic localization, and 3.4 km using multipath arrivals. Both species produced high-intensity calls; the average blue whale call source level was 189+/-3 dB re:1 microPa-1 m over 25-29 Hz, and the average fin whale call source level was 189+/-4 dB re:1 microPa-1 m over 15-28 Hz. Blue and fin whale populations in the Southern Ocean have remained at low numbers for decades since they became protected; using source level and detection range from passive acoustic recordings can help in calculating the relative density of calling whales.

Wiggins, SM, Oleson EM, McDonald MA, Hildebrand JA.  2005.  Blue whale (Balaenoptera musculus) diel call patterns offshore of southern California. Aquatic Mammals. 31:161-168.   10.1578/AM.31.2.2005.161   AbstractWebsite

Diel and seasonal calling patterns for blue whales (Balaenoptera musculus) were observed in coastal waters off southern California using seafloor-mounted autonomous acoustic recording packages (ARPs). Automated call counting from spectrogram cross-correlation showed peak seasonal calling in late summer/early fall. When call counts were organized by daily time intervals, calling peaks were observed during twilight periods, just after sunset and before sunrise. Minimum calling was observed during the day. Nighttime calling was greater than daytime calling, but also showed a minimum between the dusk and dawn calling peaks. These peaks correlate with the vertical migration times of krill, the blue whales' primary prey. One hypothesis to explain these diel variations is that blue whale calling and foraging may be mutually exclusive activities. Fewer calls are produced during the day while prey are aggregated at depth and foraging is efficient. More calls are produced during the twilight time periods when prey are vertically migrating and at night when prey are dispersed near the sea surface and foraging is less efficient.

Melcon, ML, Cummins AJ, Kerosky SM, Roche LK, Wiggins SM, Hildebrand JA.  2012.  Blue whales respond to anthropogenic noise. Plos One. 7:e32681.   doi:10.1371/journal.pone.0032681   AbstractWebsite

Anthropogenic noise may significantly impact exposed marine mammals. This work studied the vocalization response of endangered blue whales to anthropogenic noise sources in the mid-frequency range using passive acoustic monitoring in the Southern California Bight. Blue whales were less likely to produce calls when mid-frequency active sonar was present. This reduction was more pronounced when the sonar source was closer to the animal, at higher sound levels. The animals were equally likely to stop calling at any time of day, showing no diel pattern in their sensitivity to sonar. Conversely, the likelihood of whales emitting calls increased when ship sounds were nearby. Whales did not show a differential response to ship noise as a function of the time of the day either. These results demonstrate that anthropogenic noise, even at frequencies well above the blue whales' sound production range, has a strong probability of eliciting changes in vocal behavior. The long-term implications of disruption in call production to blue whale foraging and other behaviors are currently not well understood.

Širović, A, Bassett HR, Johnson SC, Wiggins SM, Hildebrand JA.  2013.  Bryde's whale calls recorded in the Gulf of Mexico. Marine Mammal Science. :n/a-n/a.   10.1111/mms.12036   AbstractWebsite

Bryde's whales (Balaenoptera edeni) inhabit tropical and subtropical waters worldwide and, unlike most other mysticetes, they are not thought to make long seasonal migrations (Jefferson et al. 2008). They are the only balaenopterid regularly found in the U.S. waters of the Gulf of Mexico (GOM), with their range likely constrained to the shallow, northeastern part of the GOM around DeSoto Canyon (Maze-Foley and Mullin, 2006). Bryde's whales are likely the smallest population of cetaceans in the region (Maze-Foley and Mullin, 2006). While it is possible Bryde's whales are present in this area year-round as four reported strandings have been recorded across seasons (Mead 1977, Jefferson and Schiro 1997, Würsig et al. 2000), visual surveys have been conducted only during the spring (Waring et al. 2009).

Kerosky, SM, Sirovic A, Roche LK, Baumann-Pickering S, Wiggins SM, Hildebrand JA.  2012.  Bryde's whale seasonal range expansion and increasing presence in the Southern California Bight from 2000 to 2010. Deep Sea Research Part I: Oceanographic Research Papers. 65:125-132.   10.1016/j.dsr.2012.03.013   AbstractWebsite

Bryde's whales (Balaenoptera edeni) are commonly found in tropical and subtropical regions of the Pacific Ocean, but few studies have explored the presence of Bryde's whales at the boundary of their distribution range. Such studies are increasingly relevant as climate impact models predict the range expansion of warm water species towards the poles in response to ocean warming. Like other baleen whales, Bryde's whales produce distinct low frequency ( <60 Hz) calls, which can be used for long-term acoustic monitoring of whale presence in an area. Autonomous passive acoustic recorders deployed at five sites in the Southern California Bight (SCB) were used to investigate the presence of Bryde's whales in temperate waters from 2000 to 2010. Calling Bryde's whales were observed in the SCB from summer to early winter, indicating a seasonal poleward range expansion. There was a significant increase in the presence of calling Bryde's whales in the SCB between 2000 and 2010, but no significant correlation was found between Bryde's whale presence and local sea surface temperature. Bryde's whale occurrence is likely driven by prey availability within the California Current ecosystem, which is affected by seasonal and inter-annual changes in climate and oceanographic conditions. Continued monitoring of Bryde's whales and their prey in the eastern North Pacific is needed to provide a longer time series and determine the full effect of climate variability and ocean warming on the distribution of this species. (C) 2012 Elsevier Ltd. All rights reserved.

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Soldevilla, MS, Henderson EE, Campbell GS, Wiggins SM, Hildebrand JA, Roch MA.  2008.  Classification of Risso's and Pacific white-sided dolphins using spectral properties of echolocation clicks. The Journal of the Acoustical Society of America. 124:609-624.: ASA   10.1121/1.2932059   AbstractWebsite

The spectral and temporal properties of echolocation clicks and the use of clicks for species classification are investigated for five species of free-ranging dolphins found offshore of southern California: short-beaked common (Delphinus delphis), long-beaked common (D. capensis), Risso's (Grampus griseus), Pacific white-sided (Lagenorhynchus obliquidens), and bottlenose (Tursiops truncatus) dolphins. Spectral properties are compared among the five species and unique spectral peak and notch patterns are described for two species. The spectral peak mean values from Pacific white-sided dolphin clicks are 22.2, 26.6, 33.7, and 37.3 kHz and from Risso's dolphins are 22.4, 25.5, 30.5, and 38.8 kHz. The spectral notch mean values from Pacific white-sided dolphin clicks are 19.0, 24.5, and 29.7 kHz and from Risso's dolphins are 19.6, 27.7, and 35.9 kHz. Analysis of variance analyses indicate that spectral peaks and notches within the frequency band 24–35 kHz are distinct between the two species and exhibit low variation within each species. Post hoc tests divide Pacific white-sided dolphin recordings into two distinct subsets containing different click types, which are hypothesized to represent the different populations that occur within the region. Bottlenose and common dolphin clicks do not show consistent patterns of spectral peaks or notches within the frequency band examined (1–100 kHz).

Roch, M. A., Soldevilla MS, Hoenigman R, Wiggins SM, Hildebrand J.  2008.  Comparison of machine learning techniques for the classification of echolocation clicks from three species of Odontocetes. Canadian Acoustics. 36:41-47. AbstractWebsite

A species detectorclassifier is presented which decides whether or not short groups of clicks are produced by one or more individuals from the following species: Blainville’s beaked whales, short- finned pilot whales, and Risso’s dolphins. The system locates individual clicks using the Teager energy operator and then constructs feature vectors for these clicks using cepstral analysis. Two different types of detectors confirm or reject the presence of each species. Gaussian mixture models (GMMs) are used to model time series independent characteristics of the species feature vector distributions. Support vector machines (SVMs) are used to model the boundaries between each species’ feature distribution and that of other species. Detection error tradeoff curves for all three species are shown with the following equal error rates: Blainville’s beaked whales (GMM 3.32%/SVM 5.54%), pilot whales (GMM 16.18%/SVM 15.00%), and Risso’s dolphins (GMM 0.03%/SVM 0.70%).

Hildebrand, JA, Wiggins SM, Henkart PC, Conyers LB.  2002.  Comparison of seismic reflection and ground-penetrating radar imaging at the controlled archaeological test site, Champaign, Illinois. Archaeological Prospection. 9:9-21.   10.1002/arp.177   Abstract

Shallow seismic reflection and ground-penetrating radar images were collected at a replicated burial mound in the Controlled Archaeological Test Site (CATS) in Champaign, Illinois. The CATS mound contains a pig burial within a wood-lined crypt at a depth of 1.6–2.4 m. Seismic reflection data were collected from two different energy sources: a small (0.5 kg) hammer for an impulsive source, and a vibrator for a frequency swept source. Seismic data were collected at densely spaced points (5 cm) along a line of 48 geophone receivers. These data were stacked in a common mid-point gather, band-pass filtered, and processed with frequency–wavenumber migration. The seismic image produced by the hammer source was dominated by bodywaves at 120 Hz, whereas the vibrator source image was dominated by surface waves at 70 Hz. Both seismic sources revealed clear reflections from the burial crypt, and placed the top of the crypt at the correct depth with a seismic velocity of 120 m s 1. The bottom of the crypt was poorly defined by the seismic data owing to multiple reflections within the crypt. The vibrator source also revealed a highfrequency (360 Hz) reflector at 2.7 m depth within the mound, perhaps due to a resonant cavity within the pig’s body. Single channel ground-penetrating radar data were processed with the same approach, including band-pass filtering and migration. The radar data reveal clear reflections from the burial crypt. Extremely fast radar velocities (260 mm ns 1) are required in the upper portion of the burial mound to place the top of the crypt at its correct depth. The bottom of the crypt was well defined by ground-penetrating radar, and was located accurately with respect to the top of the crypt with a moderate radar velocity (170 mm ns 1). The application of both seismic reflection and ground-penetrating radar to the same site may be beneficial for improved understanding of their abilities for shallow subsurface imaging. Copyright  2002 John Wiley & Sons, Ltd.

Roch, MA, Stinner-Sloan J, Baumann-Pickering S, Wiggins SM.  2015.  Compensating for the effects of site and equipment variation on delphinid species identification from their echolocation clicks. Journal of the Acoustical Society of America. 137:22-29.   10.1121/1.4904507   AbstractWebsite

A concern for applications of machine learning techniques to bioacoustics is whether or not classifiers learn the categories for which they were trained. Unfortunately, information such as characteristics of specific recording equipment or noise environments can also be learned. This question is examined in the context of identifying delphinid species by their echolocation clicks. To reduce the ambiguity between species classification performance and other confounding factors, species whose clicks can be readily distinguished were used in this study: Pacific white-sided and Risso's dolphins. A subset of data from autonomous acoustic recorders located at seven sites in the Southern California Bight collected between 2006 and 2012 was selected. Cepstral-based features were extracted for each echolocation click and Gaussian mixture models were used to classify groups of 100 clicks. One hundred Monte-Carlo three-fold experiments were conducted to examine classification performance where fold composition was determined by acoustic encounter, recorder characteristics, or recording site. The error rate increased from 6.1% when grouped by acoustic encounter to 18.1%, 46.2%, and 33.2% for grouping by equipment, equipment category, and site, respectively. A noise compensation technique reduced error for these grouping schemes to 2.7%, 4.4%, 6.7%, and 11.4%, respectively, a reduction in error rate of 56%-86%. (C) 2015 Acoustical Society of America.

Soldevilla, MS, McKenna ME, Wiggins SM, Shadwick RE, Cranford TW, Hildebrand JA.  2005.  Cuvier's beaked whale (Ziphius cavirostris) head tissues: physical properties and CT imaging. Journal of Experimental Biology. 208:2319-2332.   10.1242/jeb.01624   AbstractWebsite

Tissue physical properties from a Clavier's beaked whale (Ziphius cavirostris) neonate head are reported and compared with computed tomography (CT) X-ray imaging. Physical properties measured include longitudinal sound velocity, density, elastic modulus and hysteresis. Tissues were classified by type as follows: mandibular acoustic fat, mandibular blubber, forehead acoustic fat (melon), forehead blubber, muscle and connective tissue. Results show that each class of tissues has unique, co-varying physical properties. The mandibular acoustic fats had minimal values for sound speed (1350 +/- 10.6 m s(-1)) and mass density (890 +/- 23 kg m(-3)). These values increased through mandibular blubber (1376 +/- 13 m s(-1), 919 +/- 13 kg m(-3)), melon (1382 +/- 23m s(-1), 937 +/- 17 kg m(-3)), forehead blubber (1401 +/- 7.8 m s(-1), 935 +/- 25 kg m(-3)) and muscle (1517 +/- 46.8 m s(-1), 993 +/- 58 kg m(-3)). Connective tissue had the greatest I mean sound speed and density (1628 +/- 48.7 m s(-1)

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Gassmann, M, Wiggins SM, Hildebrand JA.  2017.  Deep-water measurements of container ship radiated noise signatures and directionality. Journal of the Acoustical Society of America. 142:1563-1574.   10.1121/1.5001063   AbstractWebsite

Underwater radiated noise from merchant ships was measured opportunistically from multiple spatial aspects to estimate signature source levels and directionality. Transiting ships were tracked via the Automatic Identification System in a shipping lane while acoustic pressure was measured at the ships' keel and beam aspects. Port and starboard beam aspects were 15 degrees, 30 degrees, and 45 degrees in compliance with ship noise measurements standards [ANSI/ASA S12.64 (2009) and ISO 17208-1 (2016)]. Additional recordings were made at a 10 degrees starboard aspect. Source levels were derived with a spherical propagation (surface-affected) or a modified Lloyd's mirror model to account for interference from surface reflections (surface-corrected). Ship source depths were estimated from spectral differences between measurements at different beam aspects. Results were exemplified with a 4870 and a 10 036 twenty-foot equivalent unit container ship at 40%-56% and 87% of service speeds, respectively. For the larger ship, opportunistic ANSI/ISO broadband levels were 195 (surface-affected) and 209 (surface-corrected) dB re 1 mu Pa-2 1 m. Directionality at a propeller blade rate of 8 Hz exhibited asymmetries in stern-bow (< 6 dB) and port-starboard (< 9 dB) direction. Previously reported broadband levels at 10 degrees aspect from McKenna, Ross, Wiggins, and Hildebrand [(2012b). J. Acoust. Soc. Am. 131, 92-103] may be similar to 12 dB lower than respective surface-affected ANSI/ISO standard derived levels. (C) 2017 Acoustical Society of America.

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.