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After decades of population growth, the central stock of the North Pacific population of humpback whales, known as the Hawai’i Distinct Population Segment (HDPS), was delisted from its endangered status in 2016. At that time, however, an unprecedented heating event, the “Pacific Marine Heatwave” (PMH) was already underway. The PMH coincided with reports of major declines of sightings of humpback whales, including calves of the year, on both the Hawaiian wintering grounds and the feeding grounds of Southeast Alaska. To examine the resiliency of the Hawai’i Distinct Population Segment, we conducted aerial surveys of the high-density Maui Nui region immediately following the PMH event in 2019 and 2020, using distance sampling methods identical to those used in an earlier series (1993 to 2003). Results showed whale densities at or above those seen earlier, with mean density for 2020 highest overall. Crude birth rates (% groups containing a calf) were similarly comparable to those recorded in the earlier series, with an increase from 2019 to 2020. Overall, results suggest the central North Pacific humpback whale population stock to be resilient in the face of this major climatic event.

Bio-logging devices are advancing the understanding of marine animal behavior, but linking sound production and behavior of individual baleen whales is still unreliable. Tag placement potentially within the near field of the sound source creates uncertainty about how tagged animal sounds will register on recorders. This study used data from a tagged singing humpback whale to evaluate this question of how sound levels present on a tag when calls are produced by a tagged animal. Root-mean-square (rms) received levels (RLs) of song units ranged from 112 to 164 dB re 1 μPa rms, with some, but not all, of the lower frequency units registering on the tag's 800 Hz accelerometer sensor. Fifty-nine percent of recorded units measured lower acoustic RLs than previously reported source levels for humpback song, but signal-to-noise ratios (SNRs) were 30–45 dB during periods of the dive with low noise. This research highlights that tag RL does not alone predict caller identity, argues for higher SNR thresholds if using SNR to inform decisions about the source of a call, and provides a baseline for future research identifying diagnostic properties of tagged animal calls in cetacean bioacoustic tag datasets.

Developing a better understanding of the stress response is critical to ensuring the health and sustainability of marine mammal populations. However, accurately measuring and interpreting a stress response in free-ranging, large cetaceans is a nascent field. Here, an enzyme immunoassay for corticosterone was validated for use in biopsy samples from male humpback whales (Megaptera novaeangliae). Analyses were conducted on 247 male North Pacific humpback whale blubber samples, including 238 non-calves and 9 calves that were collected on the Hawaiian breeding and Southeast Alaskan feeding grounds from 2004 to 2006. Significant relationships were found when corticosterone concentrations were examined by year, age class and distribution between locations. When examined by year, corticosterone concentrations for male humpback whales were higher in Hawaii in 2004 than in 2005 and 2006 (p < 0.05). Corticosterone concentration also varied by age class with initially high concentrations at birth which subsequently tapered off and remained relatively low until sexual maturity was reached around age 8-10 years. Corticosterone concentrations appeared to peak in male humpback whales around 15-25 years of age. Blubber biopsies from Alaska and Hawaii had similar mean corticosterone concentrations, yet the variability in these samples was much greater for whales located in Hawaii. It is clear that much work remains to be done in order to accurately define or monitor a stress response in male humpback whales and that specific attention is required when looking at age, sex, and yearly trends. Our results suggest that a stress response may be most impacted by age and yearly oceanographic conditions and needs to be initially examined at the individual level.

Little is known about how important social behaviors such as song vary within and among populations for any of the endemic Hawaiian honeycreepers. Habitat loss and non‐native diseases (e.g., avian malaria) have resulted in isolation and fragmentation of Hawaiian honeycreepers within primarily high elevation forests. In this study, we examined how isolation of Hawai'i ‘amakihi (Chlorodrepanis virens) populations within a fragmented landscape influences acoustic variability in song. In the last decade, small, isolated populations of disease tolerant ‘amakihi have been found within low elevation forests, allowing us to record ‘amakihi songs across a large elevational gradient (10–1800 m) that parallels disease susceptibility on Hawai'i island. To understand underlying differences among populations, we examined the role of geographic distance, elevation, and habitat structure on acoustic characteristics of ‘amakihi songs. We found that the acoustic characteristics of ‘amakihi songs and song‐type repertoires varied most strongly across an elevational gradient. Differences in ‘amakihi song types were primarily driven by less complex songs (e.g., fewer frequency changes, shorter songs) of individuals recorded at low elevation sites compared to mid and high elevation populations. The reduced complexity of ‘amakihi songs at low elevation sites is most likely shaped by the effects of habitat fragmentation and a disease‐driven population bottleneck associated with avian malaria, and maintained through isolation, localized song learning and sharing, and cultural drift. These results highlight how a non‐native disease through its influence on population demographics may have also indirectly played a role in shaping the acoustic characteristics of a species.

Passive acoustic monitoring (PAM) with autonomous bottom-moored recorders is widely used to study cetacean occurrence, distribution, and behaviors, as it is less constrained by factors that often limit other traditional visual observation methods, such as weather and accessibility. During the breeding season, male humpback whales produce an elaborate acoustic display known as “song.” The typical asynchronous chorusing of numerous singing males at any one time can provide challenges for monitoring abundance using PAM. Chorusing becomes the dominant source of low frequency (0–1.5 kHz) noise in the marine soundscape in Hawai‘i and seasonal levels mirror the whales’ migratory patterns. However, the relationship between chorusing levels and overall whale numbers, including non-singing whales (e.g., mother-calf pairs and juveniles), has remained poorly defined. We combined long-term PAM conducted between 2014/15 and 2020/21 off West Maui with concurrent visual land- and vessel-based observations. We found that daily median root-mean-squared sound pressure levels (RMS SPLs) correlate strongly with whale numbers (land: 0.71 ≤ R2 ≤ 0.76, vessel: 0.81 ≤ R2 ≤ 0.85 for three different PAM locations). Applying these results, we were able to use PAM to document significant population fluctuations between 2015 and 2021, as well as study habitat use patterns off West Maui.

— The critically endangered Hawaiian Crow or ′Alalā (Corvus hawaiiensis) is currently extinct in the wild and the remaining 115 individuals are being captively managed on Hawai′i and Maui Islands by the Zoological Society of San Diego. Here we provide the first comprehensive analysis of the vocal repertoire of this species. We documented the vocal repertoire of three male-female pairs of ′Alalā during the 2012 breeding season at the Keauhou Bird Conservation Center (KBCC) on Hawai'i Island. Vocalizations were recorded using an automated acoustic recorder placed outside each of three aviaries housing each pair of ′Alalā. A total of 44 hours of recordings were analyzed to describe the structure of vocalizations, call characteristics, and vocal repertoire of this species. We identified 24 different call type categories with fundamental frequencies between 500 Hz–2 kHz. Variation within each call type was observed, as well as variation of similar call types among ′Alalā breeding pairs. Many calls con...

For most avian species, social behaviour is critically important for survival and reproductive success. Many social behaviours in birds are culturally transmitted, and as bird populations decline across the globe, important elements of these behaviours may be lost. The Hawaiian crow or 'alalā, Corvus hawaiiensis, is a socially complex avian species that is currently extinct in the wild. As in other oscine passerines, vocalizations in the 'alalā may be culturally transmitted. We compared the vocal repertoire of three of the last four wild 'alalā pairs from the early 1990s to three current captive pairs on the Island of Hawai'i to determine how acoustic behaviour has been affected by changes in their social and physical environment. Over 18 h of recordings from wild breeding pairs were analysed and compared with 44 h from captive breeding pairs. Calls were placed into five putative behavioural categories: (1) alarm, (2) territorial broadcast, (3) aggression, (4) submission and (5) courtship. There was little difference in the overall number and diversity of call types among wild versus captive birds. However, the repertoire was significantly different. Territorial broadcast calls, common components of the wild repertoire, were absent from the captive repertoire. In addition, wild birds had twice the number of alarm calls and had a higher call rate than captive birds. Our results show how socially learned behaviours may change over relatively short periods for an entire species. Understanding how the vocal repertoire and the functional context of vocalizations change may provide useful information for ongoing efforts to reintroduce the 'alalā into the wild.

Understanding reproductive profiles and timing of reproductive events is essential in the management and conservation of humpback whales (Megaptera novaeangliae). Yet compared to other parameters and life history traits, such as abundance, migratory trends, reproductive rates, behavior and communication, relatively little is known about variations in reproductive physiology, especially in males. Here, an enzyme immunoassay (EIA) for testosterone was validated for use in biopsy samples from male humpback whales. Analyses were conducted on 277 North Pacific male humpback whale blubber samples, including 268 non-calves and 9 calves that were collected in the Hawaiian breeding grounds and the Southeast Alaskan feeding grounds from 2004 to 2006. Testosterone concentrations (ng/g) were significantly different between non-calves sampled in Hawaii (n = 182) and Alaska (n = 86, p < 0.05) with peak testosterone concentrations occurring in the winter (January-March) and the lowest concentrations occurring in the summer (June-September). Fall and spring showed increasing and decreasing trends in testosterone concentrations, respectively. Blubber testosterone concentrations in non-calves and calves sampled in Alaska were not significantly different. Blubber and skin from the same individual biopsies (n = 37) were also compared, with blubber having significantly higher testosterone concentrations (p < 0.05) than skin samples. We found variability in testosterone concentration with age, suggesting that male humpbacks reach peak lifetime testosterone concentrations in the breeding grounds around age 8-25 years. The testosterone profile of male humpback whales follows a predictable pattern for capital breeders, where testosterone begins to increase prior to the breeding season, stimulating the onset of spermatogenesis. Incorporation of reproductive hormonal profiles into our overall understanding of humpback whale physiology will shed additional light on the timing of reproduction and overall health of the recently delisted Hawaii distinct population segment (DPS).

We investigated whether calf age and calf size influence habitat choice by humpback whale motherecalf pairs in their breeding grounds. During 1997e2008, we conducted focal follows of motherecalf pairs in Hawaiian waters. Tail-fluke identification photographs and calf lengths (measured through video-grammetry) were obtained. Water depth and sea-bed terrain type were derived from GPS data. Identification photographs were matched so that the habitat choices could be established within breeding seasons. Across 72 motherecalf pairs resighted over various intervals within a breeding season, magnitude of depth change between initial and final sightings increased significantly with resighting interval. There was a significant increase from initial depth to final depth for relatively long resighting intervals (27e51 days), but no significant difference for relatively short resighting intervals (2e26 days). Although there was no preference for sea-bed terrain type by motherecalf pairs at their initial sighting, there was a preference for rugged terrain at their final resighting. A resource selection model indicated that the relative probability of a location being used by a motherecalf pair increased (as a function of water depth and rugged sea-bed terrain type) from initial to final sighting; a finding supported by subsequent tests of habitat preference versus availability. For 96 measured calves, calf length and water depth were positively correlated, even when ordinal day of measurement was controlled for statistically; a finding confirmed by a general linear model that simultaneously investigated the relationship between water depth, sea-bed terrain type, number of escorts, ordinal day and calf size. Thus, both calf age and size influence habitat choice by motherecalf pairs in their breeding grounds. The movement of mothers and their maturing calves into deeper waters where they favour rugged sea-bed terrain appears to be part of a suite of behavioural changes during the pre-migratory phase of residency in the breeding grounds.

Over the last 20 years, significant habitat shifts have been documented in some populations of cetaceans. On Little Bahama Bank (LBB) there are sympatric communities of resident Atlantic spotted dolphins (Stenella frontalis) and bottlenose dolphins (Tursiops truncatus), monitored since 1985. The size and social structure (three clusters: Northern, Central, Southern) have been stable among the spotted dolphin community with little immigration/emigration, even after large demographic losses (36%) following two major hurricanes in 2004. In 2013 an unprecedented exodus of over 50% (52 individuals) of the spotted dolphin community was documented. The entire Central cluster and a few Northern and Southern individuals relocated 161 km south to Great Bahama Bank (GBB), also home to two sympatric resident communities of spotted dolphins and bottlenose dolphins. During the late summer of 2013 and the summers of 2014 and 2015 both sites were regularly monitored but no former LBB dolphins returned to LBB. Uncharacteristic matriline splits were observed. Social analyses revealed random associations for those spotted dolphins and very little integration between spotted dolphins that moved to GBB (MGBB) and those dolphin resident to GBB (RGBB). Male alliances among spotted dolphins were present, with some altered patterns. On LBB, the operational sex ratio (OSR) was reduced (.40 to .25). OSR for MGBB and RGBB dolphins were similar (.45 and .43). A significant steady decrease in sea surface temperature and chlorophyll a (a proxy for plankton production) occurred on LBB leading up to this exodus. Similar trends were not present over the same period on GBB. The sudden large-scale shift of spotted dolphins from LBB to GBB in association with the gradual decline in certain environmental factors suggests that a possible "tipping point" was reached in prey availability. This study provides a unique view into social and genetic implications of large-scale displacement of stable dolphin communities.

Humpback whales congregate annually in low-latitude winter breeding and calving grounds. While on these grounds, females with a dependent calf (‘maternal females’) are sometimes closely attended by one or more male escorts. Using data collected from a shore-based observation platform in the Hawaiian Islands, we tested the hypothesis that the spatial distribution of maternal females is driven primarily by avoidance of males. As predicted, we found that (1) pods containing a calf occurred in significantly shallower water than pods that did not contain a calf, (2) unescorted maternal females occurred in significantly shallower water than escorted maternal females, (3) the number of males escorting a female decreased significantly with decreasing water depth, and (4) the swimming speed of maternal females increased as a function of male presence, with escorted females travelling significantly more rapidly than unescorted females and a significant positive correlation between swimming speed and number of escorts. We suggest that maternal females incur increased energetic costs when escorted by males and consequently position themselves in shallow waters to reduce the likelihood of unwanted male attention.

While on their winter breeding grounds, male humpback whales (Megaptera novaeangliae) produce long sequences of structured vocalizations called song, whose function within the mating system is still unresolved. Here we ask which males sing. Is it only those sexually mature, as typifies songbirds and some lekking ungulates in which vocalizations during the rut are restricted to mature males? Or do immature males join in the chorus? Using an under- water videogrammetric technique, we measured the body lengths of 87 humpback singers in the Hawaiian winter grounds. Applying length and sexual maturity relationships for North Pacific humpbacks as determined by biologists aboard twentieth century Japanese whaling vessels, we found that singer lengths ranged from 10.7 to 13.6 m, with 15 % of lengths indicative of probable sexual immaturity (length

It has been hypothesized that protecting herbivorous fishes within Marine Reserves (MRs) will help these areas to resist algal overgrowth of corals. However, we lack empirical studies demonstrating the validity of key assumptions underpinning this concept, including that herbivorous fishes (1) are permanently resident within MR boundaries, (2) routinely consume the invasive algae of concern at significant levels and (3) are not significant mobile vectors for propagules of the invasive algae. A 46-year-old MR (Hawaii Marine Laboratory Refuge, 21°27′35″N, 157°48′15″W) in waters off Oahu provided a natural setting to examine these factors with the herbivorous bluespine unicornfish (Naso unicornis) and the invasive rhodophyte, Gracilaria salicornia. We acoustically tracked five unicornfish to quantify their residency and habitat use within the MR, conducted field and laboratory observations to confirm N. unicornis consume G. salicornia, and tested the viability of G. salicornia fragments recovered from unicornfish feces. Unicornfish were resident within the MR where they spent most time in reef crest habitat with occasional, brief forays into reef flat habitat. We confirmed unicornfish consume G. salicornia and found a significant positive correlation between algal canopy height and distance from the reef crest, presumably because grazing intensity is lower in less frequently utilized reef flat habitat. We demonstrated that unicornfish egest viable fragments of G. salicornia that resume vegetative growth after several weeks. We conclude that N. unicornis may act as both a natural control agent and a mobile vector for invasive alien algae.

Male humpback whales produce loud “songs” on the wintering grounds and some sing while escorting mother–calf pairs, exposing them to near-continuous sounds at close proximity. An Acousonde acoustic and movement recording tag deployed on a calf off Maui, Hawaii captured sounds produced by a singing male escort. Root-mean-square received levels ranged from 126 to 158 dB re 1 μPa. These levels represent rare direct measurements of sound to which a newly born humpback calf may be naturally exposed by a conspecific, and may provide a basis for informed decisions regarding anthropogenic sound levels projected near calves.

Assortative pairing, and its relation to mate choice, has rarely been documented in mammals. Using data collected during 1998–2007, we investigated size-assortative pairing as it relates to discrimination amongst potential mates in humpback whale, Megaptera novaeangliae, dyads in the Hawaiian breeding grounds. Across 67 male–female dyads in which both individuals were measured using underwater videogrammetry, male length was positively correlated with female length. Detailed analyses on the assessment of maturity by comparisons with whaling data revealed that mature-sized females associated almost exclusively with mature-sized males and had a significant preference for large mature-sized males. In contrast, mature-sized males were less discriminating in their associations with females and showed no significant preference for mature-sized females. However, mature-sized males that associated with immature-sized females were significantly smaller than males that associated with mature-sized females. Finally, immature-sized males tended to associate with immature-sized females. The sex differences in size preference by mature whales probably reflect the relatively high costs of mature females mating with small or immature males compared to the lower costs of mature males mating with small or immature females. Body size appears to influence the adoption of alternative mating tactics by males such that smaller mature males avoid the costs of competing for the highest-quality females and instead focus their attentions on smaller females that may or may not be mature. Overall, our results provide the first quantitative evidence of size-assortative pairing and female discrimination amongst potential mates in humpback whales and indeed in any cetacean species.

From a database of approximately 5,000 Hawaiian humpback whales identified photographically between 1976 and 2010, we extracted 71 males and 39 females having resighting spans of 10 or more years, from first to most recent sighting. Findings included: (1) the male-biased sex ratio was like that found in breeding grounds worldwide; (2) the mean span for males of 20.7 yr (maximum = 32 yr) did not differ significantly from the mean of 19.8 yr (maximum = 29 yr) for females, but males were seen in significantly more years during their spans than were females; (3) the mean number of females seen with and without calf across 11 three-year intervals from 1977 to 2009 did not differ significantly; (4) the calving rate for the 39 females was 0.48 and seven females produced two to eight calves over spans of 22–26 yr; (5) females attracted significantly more escorts in years without calf than in years with calf; (6) individuals showed great diversity in the social units they occupied over their sighting spans, but with the most frequently observed unit for both sexes being the trio of mother, calf, and escort. Males were also observed frequently in competitive groups centered about a female without calf.

Invasive tags designed to provide information on animal movements through radio or satellite monitoring have tremendous potential for the study of whales and other cetaceans. However, to date there have been no published studies on the survival of tagged animals over periods of years or decades. Researchers from the National Marine Mammal Laboratory and the Woods Hole Oceanographic Institution tracked five humpback whales with implanted radio tags in southeastern Alaska in August 1976 and July 1977, and tracked two humpback whales in Prince William Sound, Alaska, in June 1978. All seven of these individually identified humpback whales were resighted at least 20 yr after first being tagged, and five of the seven have been observed for more than 30 yr; some of them are among the most resighted humpback whales in the North Pacific. Photos of tagging sites taken during and subsequent to tagging operations show persistent but superficial scarring and no indication of infection. These pioneering field studies demonstrated both long-term survival of the whales and the short-term effects of deploying radio tags, which at the time were larger and more invasive than those typically used today.

Objectives/Hypothesis: Recent studies in animal models have shown via physiologic and histologic measures that the administration of exogenous antioxidants is protective against gentamicin-induced oto-vestibulo toxicity. In addition, studies have also shown that sound conditioning increases cochlear antioxidants. The objective of this study is to determine wether sound conditioning provides protection against gentamicin in the cochlear and/or vestibular system. Study Design: Prospective animal study. Methods: Three-month-old gerbils were divided into three groups (A, B, and C). The gerbils in group A were sound conditioned only (n = 2). In group B, the animals received gentamicin on the round window (n = 2). The gerbils in group C were sound conditioned first and later received gentamicin to the round window (n = 2). The animals were ultimately sacrificed and their right cochlea and posterior crista ampullaris were removed, processed, and sectioned. The specimens were analyzed for inner hair cell (IHC) and outer hair cell (OHC) loss and vestibular supporting and sensory hair cell nuclei per micrometer of vestibular epithelium. Results: The sound-conditioned group (A) had no loss of cochlear hair cells. The gerbils treated with gentamicin only (B) had a 34% decrease of OHCs and 49% decrease of IHCs. The sound-conditioned plus gentamicin-treated group (C) had a 5.5% decrease in OHCs and 12% decrease in IHCs. There were no significant differences with regards to supporting cell nuclei within the posterior crista across all groups. When compared to group A, the gerbils in groups B and C did have a 23 to 42% decrease in the number of sensory cell nuclei per micrometer of vestibular epithelium. Conclusions: Sound conditioning does appear to attenuate the effects of gentamicin in the cochlea, although not significantly altering its vestibulotoxicity. An upregulation of cochlear-specific antioxidants is believed to be an important factor. As we had a small sample size, we can only note trends in the data, but future studies with more animals and measurements of antioxidant levels after sound conditioning would be useful to quantify this effect and determine if it can be exploited clinically.

Pacinian corpuscles (PCs) are tactile receptors composed of a nerve ending (neurite) that is encapsulated by layers of lamellar cells. PCs are classified as primary mechanoreceptors because there is no synapse between the transductive membrane and the site of action-potential generation. These touch receptors respond in a rapidly adapting manner to sustained pressure (indentation or displacement), which until now was believed to be attributable solely to the mechanical properties of the capsule. However, evidence of positive immunoreactivity for GABA receptors on the neurite, as well as evidence for gene expression of synaptobrevin in the lamellar cells led to the hypothesis that GABAergic inhibition originating from the lamellar cells is involved in the rapid adaptation process of PCs. Electrophysiological data from isolated PCs demonstrates that, in the presence of either gabazine or picrotoxin (GABA receptor antagonists), many action potentials appear during the static portion of a sustained indentation stimulus (similar to slowly adapting receptors) and that these “static” spikes completely disappear in the presence of GABA. It was consequently hypothesized that glutamate, released by either the neurite itself or the lamellar cells, caused these action potentials. Indeed, the glutamate receptor blocker kynurenate either decreased or totally eliminated the static spikes. Together, these results suggest that GABA, emanating from the modified Schwann cells of the capsule, inhibits glutamatergic excitation during the static portion of sustained pressure, thus forming a “mechanochemical,” rather than purely mechanical, rapid adaptation response. This glial–neuronal interaction is a completely novel finding for the PC.

The competitive group appears to be a major component of the mating system of the humpback whale, Megaptera novaeangliae, bringing together a single female (nuclear animal or NA) and multiple males (escorts) that compete for physical proximity to her. We examined the relation of body size of the NA to the number of attending escorts and, separately, we determined the relation of a female’s body size to the size of her calf. Using underwater videogrammetry in Maui waters during 1997–2002, we measured the body length of the NA in each of 42 competitive groups. We also measured the lengths of the mother and her calf in each of 92 mother–calf groups. The number of initial escorts in a competitive group was positively correlated with NA body length. Longer mothers were associated with longer calves, even after accounting for seasonal differences in calf length. We conclude that male humpback whales prefer to associate with larger females and that larger females produce larger calves. Theoretically, larger calves have a greater chance of survival than do smaller calves. The choice of a larger female may therefore increase the reproductive success of an escort that succeeds in mating.

Pacinian corpuscles (PCs) in cat mesentery have been studied extensively to help determine the structural and functional bases of tactile mechanotransduction. Although we, like many other investigators, have found that the mesenteric receptors are anatomically very similar to those found in mammalian skin, few physiological characteristics of the mesenteric PCs and those of the skin have been compared. Action-potential rate-amplitude and frequency characteristics (10 Hz-1 KHz), as well as interval (IH) and peri-stimulus-time (PSTH) histograms in response to sinusoidal displacements were obtained from nerve fibers innervating mesenteric PCs and from PC fibers innervating cat glabrous skin. The intensity characteristics obtained on both preparations showed similar response profiles, including equal slopes for low stimulus intensities (approximately 10, with impulse ratios/20 dB displacement) and one and two impulse/cycle entrainment. The frequency characteristics of both groups were U-shaped with similar low-frequency slopes (-12.5 dB/octave) and bandwidths (Q(3dB) = 1.4). The best frequency for both the tactile PCs' and mesenteric PCs was 250 Hz, which is in the expected range. The IHs showed entrainment and the PSTHs showed neither transient responses nor adaptation to steady-state sinusoidal stimuli. The functional similarity between mesenteric PCs' nerve responses and those of tactile PC afferents, as well as the receptors' anatomical similarity, lead us to suggest that the mesenteric PC can act as a model for those in the skin. Furthermore, since the frequency characteristics of the two PC types are similar, it is concluded that the skin, while attenuating stimulus intensity, does not impart temporal filtering of vibratory stimuli.

Despite years of study, the humpback whale mating system remains an enigma. Sustained observations of subsurface behavior may help reveal important components of the mating system. In 2005 and 2006, we deployed Crittercam, an animal-borne imaging and data-logging tool, on humpback whales in their winter grounds. We focused our efforts on competitive groups, believed to be the epicenter of mate selection. Over 27 days of fieldwork in Maui waters we deployed 10 front- or rear-facing Crittercams on escorts (males) in competitive groups. This work revealed: (1) Five whales swimming to depths of over 150 m, with one animal diving down 298 m; (2) Instances of competitive behavior (inflated pleats, chasing) occurring along the seafloor; (3) The displacement of a primary escort (the whale closest to the female) by a challenger; (4) A detailed time budget of one principal escort maintaining his position over a 73-min observation window; (5) Threats and body strikes between secondary escorts; (6) Apparent affiliative behavior by females, including possible pectoral fin stroking of a principal escort and drafting in a principal escort's pressure wave; and (7) A secondary escort resting on the bottom while sculling its pectoral fins through the substrate, throwing up clouds of sand. In summary, Crittercam allowed us to observe diving behavior and sustained micro-interactions between animals in competitive groups occurring far below the surface. Such observations can have significant bearing on interpretation of the mating system by assisting in uncovering behaviors that may be involved in mate guarding, dominance hierarchies, and female choice.

A bottlenose dolphin was tested on its ability to echoically discriminate horizontal angular differences between arrays of vertically oriented air-filled PVC rods. The blindfolded dolphin was required to station in a submerged hoop 2 radial m from the stimuli and indicate if an array with two rods (S+) was to the right or the left of a single rod (S-). The angular separation between the two rods (thetaw) was held constant within each experiment while the angle between the S+ and the S-stimuli (thetab) varied to produce angular differences (deltatheta= thetab-thetaw) ranging from 0.25 to 4 degrees. In experiment I, thetaw was maintained at 2 degrees and in experiment II, thetaw was maintained at 4 degrees. Resulting 75% correct thresholds (method of constant stimuli) were 1.5 and 0.7 degrees, respectively. The two main findings of this study are: (1) decreasing the number of targets does not aid in localization, and (2) increasing the space between the rods enhances localization. Taken as a whole, the experiments suggest dolphins have a well-developed ability to resolve spatial information through sonar.

Recent intense interest in social cognition in dolphins reflects findings that wild dolphins live in complex societies that rely on individual recognition, a protracted period of development, coalition formation, and cooperative, as well as competitive, social behaviors. Laboratory studies have revealed a host of cognitive skills that can support such complex behaviors—for example, broad imitative abilities, abilities to understand another’s indicative cues, and spontaneous use of pointing to communicate with human companions. Joint attention is recognized as a key element of social cognition that extends from simply following another’s gaze to using pointing or gazing cues of another to select objects or locations. Studies of bottlenose dolphins (Tursiops truncatus) have revealed that they understand (1) human-given direct and cross-body points; (2) human-given dynamic and static pointing and gazing cues within object-choice tasks; (3) the geometry of pointing cues; (4) the referential character of pointing and gazing cues; (5) sequences of direct and/or crossbody points that were instructions to transport one object to another; (6) how to produce pointing cues and the importance of audience attention; and (7) possibly the belief state of another that is engaged in a joint attention task. The evidence suggests that joint attention skills in dolphins are robust and to some degree symmetric across comprehension and production. Comparative analyses indicate that in some areas of joint attention, abilities of dolphins exceed the demonstrated skills of apes. Possibly, a dolphin’s capacity for joint attention may be related to the adaptive benefits of being able to attend to the focus of another dolphin’s echolocation beam in conjunction with a sophisticated social structure dependent on attention to others. Correspondence: A. A. Pack, The Dolphin Institute, 420 Ward Avenue, Suite 212, Honolulu, HI 96814, USA (E-mail: pack@hawaii.edu)

A vertical array of five hydrophones was used to measure the acoustic field in the vertical plane of singing humpback whales. Once a singer was located, two swimmers with snorkel gear were deployed to determine the orientation of the whale and position the boat so that the array could be deployed in front of the whale at a minimum standoff distance of at least 10 m. The spacing of the hydrophones was 7 m with the deepest hydrophone deployed at a depth of 35 m. An eight-channel TASCAM recorder with a bandwidth of 24 kHz was used to record the hydrophone signals. The location (distance and depth) of the singer was determined by computing the time of arrival differences between the hydrophone signals. The maximum source level varied between individual units in a song, with values between 151 and 173 dB re 1 microPa. One of the purposes of this study was to estimate potential sound exposure of nearby conspecifics. The acoustic field determined by considering the relative intensity of higher frequency harmonics in the signals indicated that the sounds are projected in the horizontal direction despite the singer being canted head downward anywhere from about 25 degrees to 90 degrees. High-frequency harmonics extended beyond 24 kHz, suggesting that humpback whales may have an upper frequency limit of hearing as high as 24 kHz.

Objective To evaluate patterns of ototoxic damage sustained from gentamicin applied directly to the round window in varying delivery vehicles. Setting The search for a reliable method of drug delivery to the inner ear continues. Vehicles such as Gelfoam, hyaluronic acid, and fibrin may allow for a more reproducible pattern of ototoxic damage. Study design Histological evaluation of vestibular and cochlear damage was performed on Mongolian gerbils after a known dosage of gentamicin in different delivery vehicles. Results Variable ototoxic damage was caused by Gelfoam and fibrin-based vehicles. No ototoxic damage was found in the Healon vehicle. The vehicle of fibrin and Gelfoam combined resulted in severe damage. There was no evidence of selective cochlear or vestibular ototoxicity in any of the vehicles tested. Conclusions and significance The fibrin/Gelfoam vehicle was the only delivery system to produce reliable damage. Ototoxic damage depended on the vehicle. We found no evidence for selective vestibular ototoxicity with gentamicin.

Male humpback whales (Megaptera novaeangliae) produce long, structured sequences of sound underwater, commonly called "songs." Humpbacks progressively modify their songs over time in ways that suggest that individuals are copying song elements that they hear being used by other singers. Little is known about the factors that determine how whales learn from their auditory experiences. Song learning in birds is better understood and appears to be constrained by stable core attributes such as species-specific sound repertoires and song syntax. To clarify whether similar constraints exist for song learning by humpbacks, we analyzed changes over 14 years in the sounds used by humpback whales singing in Hawaiian waters. We found that although the properties of individual sounds within songs are quite variable over time, the overall distribution of certain acoustic features within the repertoire appears to be stable. In particular, our findings suggest that species-specific constraints on temporal features of song sounds determine song form, whereas spectral variability allows whales to flexibly adapt song elements.

The authors tested 2 bottlenosed dolphins (Tursiops truncatus) for their understanding of human-directed gazing or pointing in a 2-alternative object-choice task. A dolphin watched a human informant either gazing at or pointing toward 1 of 2 laterally placed objects and was required to perform a previously indicated action to that object. Both static and dynamic gaze, as well as static and dynamic direct points and cross-body points, yielded errorless or nearly errorless performance. Gaze with the informant's torso obscured (only the head was shown) produced no performance decrement, but gaze with eyes only resulted in chance performance. The results revealed spontaneous understanding of human gaze accomplished through head orientation, with or without the human informant's eyes obscured, and demonstrated that gaze-directed cues were as effective as point-directed cues in the object-choice task.