Gordon B. Bauer

Magnetoreception and Biomineralization of Magnetite in Cetaceans

Living cetaceans comprise two suborders, Mysticeti (the baleen whales) and Odontoceti (the toothed whales). Within both groups are species which migrate over extended areas (reviews in Kinne, 1975; Baker, 1978). In general, the mysticetes are more predictable in their migration patterns and appear to range over a larger area. Although much remains to be learned about specific migration routes, it is probably safe to say that most mysticetes follow a similar pattern. They feed during the summer in polar and subpolar waters and breed in temperate to tropical waters in the winter. Bowhead whales, which are predominantly arctic in distribution, and Bryde’s whales, which are primarily tropical, appear to be the only exceptions. The migrations between feeding and breeding grounds can be extensive, e.g., 5000 miles in the case of the gray whale (Pike, 1962). They can also be remarkable in their precision, e.g., humpback whales are able to locate the Hawaiian Islands after a journey over thousands of miles of open ocean on their southern journey from Alaska (Baker et al., 1982; Darling and Jurasz, 1983; Darling and McSweeny, 1983). The odontocetes have less spectacular migrations, but they still travel over substantial stretches of ocean.

Magnetoreception and Biomineralization of Magnetite in Amphibians and Reptiles

Many amphibians and reptiles are seasonally migratory, traveling to and from suitable breeding, feeding, or hibernation grounds. These creatures also carry out small-scale directed movements in local areas. As juveniles, they must locate appropriate areas for growth and maturation, often in environments vastly different from those into which they hatched. Thus, soon after hatching, sea turtles scrabble up through the sand and find their way down the beach to the ocean, while tadpoles, after spending several weeks in an aquatic environment, metamorphose into frogs and climb out of their ponds onto dry land. As adults, the amphibians and reptiles slither, stalk, or swim about in search of food and shelter and to escape predators.

Audiogram and auditory critical ratios of two Florida manatees ( Trichechus manatus latirostris )

SUMMARY Manatees inhabit turbid, shallow-water environments and have been shown to have poor visual acuity. Previous studies on hearing have demonstrated that manatees possess good hearing and sound localization abilities. The goals of this research were to determine the hearing abilities of two captive subjects and measure critical ratios to understand the capacity of manatees to detect tonal signals, such as manatee vocalizations, in the presence of noise. This study was also undertaken to better understand individual variability, which has been encountered during behavioral research with manatees. Two Florida manatees (Trichechus manatus latirostris) were tested in a go/no-go paradigm using a modified staircase method, with incorporated ‘catch’ trials at a 1:1 ratio, to assess their ability to detect single-frequency tonal stimuli. The behavioral audiograms indicated that the manatees’ auditory frequency detection for tonal stimuli ranged from 0.25 to 90.5 kHz, with peak sensitivity extending from 8 to 32 kHz. Critical ratios, thresholds for tone detection in the presence of background masking noise, were determined with one-octave wide noise bands, 7–12 dB (spectrum level) above the thresholds determined for the audiogram under quiet conditions. Manatees appear to have quite low critical ratios, especially at 8 kHz, where the ratio was 18.3 dB for one manatee. This suggests that manatee hearing is sensitive in the presence of background noise and that they may have relatively narrow filters in the tested frequency range.

Responses of wintering humpback whales to vessel traffic

Responses of humpback whales to vessel traffic were monitored over two winter seasons during 1983–1984 in Maui, Hawaii. A variety of vessel characteristics including vessel numbers, speed, and proximity were associated with changes in whale behaviors, including swimming speed, respiration, and social behaviors. Smaller pods and pods with a calf were more affected than larger pods. A case study indicated that a calf could be sensitized by the passby of a large vessel, so that it subsequently breached in response to noise from a smaller boat engine which had not previously elicited any behavior change. These findings in conjunction with similar results from summering humpbacks in Alaska indicated disturbance of humpback whales at both ends of their range. Although substantial short‐term effects were noted, long‐term negative consequences are not apparent. Recent aerial surveys of the Hawaiian Islands indicate substantial increases in the number of humpback whales.

Impact of assertive and accusatory communication of distress and anger: A verbal component analysis

Forty undergraduate women were asked to imagine discussing an important problem in their relationship with a personally close partner and to rate likely emotional and behavioral reactions to four kinds of statements: 1) assertive communication of distress, 2) assertive communication of anger, 3) accusatory communication of distress, and 4) accusatory communication of anger. Accusatory “you” statements were rated as more aversive and evoked more negative emotional and behavioral response inclinations than did assertive “I” messages. Statements including “anger” words evoked more negative emotional and behavioral response inclinations than statements including “distress” words. Findings were related to research on cue-controlled aggression and the work of Staats, which predicts ways that verbal labels (language) exert control over emotions and behavior.

Four-choice sound localization abilities of two Florida manatees,Trichechus manatus latirostris

SUMMARY The absolute sound localization abilities of two Florida manatees (Trichechus manatus latirostris) were measured using a four-choice discrimination paradigm, with test locations positioned at 45 deg., 90 deg., 270 deg. and 315 deg. angles relative to subjects facing 0 deg. Three broadband signals were tested at four durations (200, 500, 1000, 3000 ms), including a stimulus that spanned a wide range of frequencies (0.2–20 kHz), one stimulus that was restricted to frequencies with wavelengths shorter than their interaural time distances (6–20 kHz) and one that was limited to those with wavelengths longer than their interaural time distances (0.2–2 kHz). Two 3000 ms tonal signals were tested, including a 4 kHz stimulus, which is the midpoint of the 2.5–5.9 kHz fundamental frequency range of manatee vocalizations and a 16 kHz stimulus, which is in the range of manatee best-hearing sensitivity. Percentage correct within the broadband conditions ranged from 79% to 93% for Subject 1 and from 51% to 93% for Subject 2. Both performed above chance with the tonal signals but had much lower accuracy than with broadband signals, with Subject 1 at 44% and 33% and Subject 2 at 49% and 32% at the 4 kHz and 16 kHz conditions, respectively. These results demonstrate that manatees are able to localize frequency bands with wavelengths that are both shorter and longer than their interaural time distances and suggest that they have the ability to localize both manatee vocalizations and recreational boat engine noises.

Manatee vibrissae: evidence for a “lateral line” function

Aquatic mammals use vibrissae to detect hydrodynamic stimuli over a range from 5 to 150 Hz, similar to the range detected by lateral line systems in fishes and amphibians. Manatees possess ∼5,300 vibrissae distributed over the body, innervated by ∼209,000 axons. This extensive innervation devoted to vibrissae follicles is reflected in enlarged, elaborate somatosensory regions of the gracile, cuneate, and Bischoffs brain‐stem nuclei, ventrobasal thalamus, and presumptive somatosensory cortex. Our preliminary psychophysical testing indicates that in Florida and Antillean manatees the Weber fraction for detection thresholds for grating textures ranges from 0.025 to 0.14. At the lower end of this range, sensitivity is comparable to human index finger thresholds. For hydrodynamic stimuli of 5–150 Hz, detection threshold levels for manatees using facial or postfacial vibrissae were substantially lower than those reported for harbor seals and similar to reports of sensitivity for the lateral line systems of some fish. Our findings suggest that the facial and postfacial vibrissae are used to detect hydrodynamic stimuli, whereas only the facial vibrissae are used for direct contact investigation.

The mimetic Dolphin

Rendell and Whitehead note the necessary, complementary relationship between field and laboratory studies in other species, but conclude their article by de-emphasizing the role of laboratory findings in cetacean research. The ambiguity in field studies of cetaceans should argue for greater reliance on the laboratory, which has provided much of the available research supporting the hypothesis of cetacean culture.

Auditory evoked potential measurements with cetaceans

Auditory evoked potentials (AEPs) allow researchers to measure the hearing abilities of animals that would be difficult or impossible to train for behavioral measurements of hearing. The hearing abilities of live‐stranded cetaceans and wild dolphins can only be made with AEP techniques. In these situations, time with the animal is often restricted to an hour or less, and there is often little control over the acoustic environment in which the tests are performed. AEP measurements may be made while the animals are in air or in shallow pools. For cetaceans in air, sounds are typically presented with a suction cup jawphone. For cetaceans in water, sounds may be presented in a direct field (with the transducer located at some distance from the test subject) or with a jawphone. In each of these situations it is important to understand how thresholds derived from AEP measurements compare with behavioral hearing measurements. Examples of AEP measurements from wild and live‐stranded cetaceans are presented to ill...

Evoked potential measurements of the West Indian manatee modulation rate transfer function

Evoked potential measurements of two Florida manatees (Trichechus manatus latirostris) suggest that these herbivores have evolved an auditory system with high temporal resolution. The manatee modulation rate transfer function (MRTF) is maximally sensitive to a 600‐Hz amplitude modulation (AM) rate. This modulation rate is midway between the AM sensitivities of terrestrial mammals (chinchillas, gerbils, and humans) (80–150 Hz) and dolphins (1000–1200 Hz). We also demonstrate evoked potential responses to carrier frequencies up to 40 kHz. These results suggest that manatees may have reasonable underwater localization abilities despite the high speed of sound underwater, which could be important in enabling them to localize oncoming boats.