Louis M. Herman

Acoustic properties of humpback whale songs

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.

Underwater frequency discrimination in the bottlenosed dolphin (1–140 kHz) and the human (1–8 kHz)

Frequency difference limens (DLs) were obtained for frequencies (F) from 1 to 140 kHz for the bottlenosed dolphin, Tursiops truncatus (Montagu), and from 1 to 8 kHz for two human subjects tested underwater. Discriminations were required between constant‐frequency (pure‐tone) signals and frequency‐modulated signals, using a successive discrimination procedure. Relative DLs (DL/F) for the dolphin generally ranged from 0.002 to 0.004 between 2 and 53 kHz, and never exceeded 0.008 through to 130 kHz; at 1 and 140 kHz, relative DLs increased to 0.014. No responses were obtainable at 150 kHz. These findings demonstrate excellent frequency discrimination throughout the audible spectrum (above 1 kHz) of Tursiops and support electrophysiological evidence of highly sensitive frequency detection mechanisms. Results for the humans showed smaller DLs than the dolphin at 1 kHz, approximately equal DLs at 2 kHz, and progressively larger DLs at 4 and 8 kHz. The human underwater thresholds were generally consistent with t...

Bottlenosed Dolphins (Tursiops truncatus) Comprehend the Referent of Both Static and Dynamic Human Gazing and Pointing in an Object-Choice Task

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 informants 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 informants eyes obscured, and demonstrated that gaze-directed cues were as effective as point-directed cues in the object-choice task.

MEMORY FOR RECENT ACTIONS IN THE BOTTLENOSED DOLPHIN (TURSIOPS TRUNCATUS) : REPETITION OF ARBITRARY BEHAVIORS USING AN ABSTRACT RULE

Little is known about how animals represent their own actions in working memory. We investigated whether bottlenosed dolphins could recall actions they had recently performed and reveal those recollections using an abstract rule. Two dolphins were trained to respond to a specific gestural command by repeating the last behavior performed. Both dolphins proved to be able to repeat a wide variety of behaviors on command and were able to generalize the repeating rule to novel behaviors and situations. One dolphin was able to repeat all 36 behaviors she was tested on, including behaviors involving multiple simultaneous actions and self-selected behaviors. These results suggest that dolphins can flexibly access memories of their recent actions and that these memories are of sufficient detail to allow for reenactments. The repeating task can potentially be used to investigate short-term action and event representations in a variety of species.

Bottlenosed dolphin and human recognition of veridical and degraded video displays of an artificial gestural language.

2 bottlenosed dolphins proficient in interpreting gesture language signs viewed veridical and degraded gestures via TV without explicit training. In Exp. 1, dolphins immediately understood most gestures: Performance was high throughout degradations successively obscuring the head, torso, arms, and fingers, though deficits occurred for gestures degraded to a point-light display (PLD) of the signers hands. In Exp. 2, humans of varying gestural fluency saw the PLD and veridical gestures from Exp. 1. Again, performance declined in the PLD condition. Though the dolphin recognized gestures as accurately as fluent humans, effects of the gestures formational properties were not identical for humans and dolphin. Results suggest that the dolphin uses a network of semantic and gestural representations, that bottom-up processing predominates when the dolphins short-term memory is taxed, and that recognition is affected by variables germane to grammatical category, short-term memory, and visual perception.

Responses of wintering humpback whales (Megaptera novaeangliae) to playback of recordings of winter and summer vocalizations and of synthetic sound

SummaryThree natural sounds and one synthetic sound were played back to humpback whales during their 1985 and 1986 winter residency in Hawaiian waters. Playback was conducted from a vessel positioned within visual range of an elevated shorestation equipped with a high-precision surveyors theodolite, used to determine the positions and movements of observed whale and of the playback vessel. A playback session consisted of 20 min of pretest observation with the vessel in place and underwater speaker deployed, followed by a 20-min test phase during which sound, or a blank tape control, was introduced. A total of 143 playback sessions, involving a total of 338 pods (a single whale or a group of whales), were completed over the two winter seasons. The major response observed during playback was a rapid approach to the playback vessel, characterized in some cases by velocities up to 9 km/h and approaches to within 50 m or less. Whales approaching were mainly singletons and, secondly, apparent adult pairs. No cow-calf pair ever approached. The approach was selective: 21.6% of targeted pods approached in response to a feeding sound recorded in summer feeding grounds in Alaska; 8.3% approached in response to social sounds recorded in the Hawaiian winter grounds in the presence of large surface-active pods; 3.4% responded to playback of winter song; and 4.1% responded to playback of synthetic sound. There were no approach responses to the blank tape control. Singing whales have been identified as males by many researchers. Data from Alaska suggested that the feeding sound was produced by a female; data from Hawaii suggests that the social sounds were produced by males. The different rates of response were attributed to the behavior of sexually active males seeking to affiliate with sexually mature females. Although a female may be present in pods producing social sounds, the presence of multiple males exhibiting aggression may inhibit the approach of other males. Song did not serve as an attractant for females, as measured by direct approach, but may still serve as a basis for female choice.

Migratory Timing of Humpback Whales ( Megaptera novaeangliae ) in the Central North Pacific Varies with Age, Sex and Reproductive Status

Humpback whales migrate seasonally between high-latitude summer feeding grounds and low-latitude winter breeding grounds. Identification photographs of humpback whales were collected in the Hawaiian Islands between 1977 and 1995, and sighting histories were compiled for individuals. Analyses revealed that (a) mean dates of first identification were significantly earlier for juveniles and females with no calf than for males and females with a calf off the Big Island, and significantly earlier for juveniles than for females with no calf, males and females with a calf off Maui; and (b) mean dates of last identification were significantly earlier for juveniles and females with no calf than for males and females with a calf off the Big Island, and significantly earlier for females with no calf than for males and females with a calf off Maui. A within-subjects comparison showed that the date of first identification tended to be later for individual females in the years when they had a calf than in the years during which they had no calf. It was concluded that (a) migratory timing varies as a function of age, sex and reproductive status, (b) migratory timing is intimately connected with reproductive success and (c) migratory timing has important consequences for our understanding of humpback whale behaviour on the winter grounds.

Humpback Whale Song: Our Current Understanding

More than 20 years have elapsed since the first detailed descriptions of humpback whale song (Payne and McVay, 1971; Winn, Perkins and Poulter, 1971) and despite considerable attention, the function of song remains elusive. In this paper, we review the literature on humpback whale song and describe general methods used to collect data on free-ranging whales. Then, we present the results of three current studies that have used different methods to shed light on the function of whale song.

Seeing through sound: dolphins (Tursiops truncatus) perceive the spatial structure of objects through echolocation.

Experiment 1 tested a dolphin (Tursiops truncatus) for cross-modal recognition of 25 unique pairings of 8 familiar, complexly shaped objects, using the senses of echolocation and vision. Cross-modal recognition was errorless or nearly so for 24 of the 25 pairings under both visual to echoic matching (V-E) and echoic to visual matching (E-V). First-trial recognition occurred for 20 pairings under V-E and for 24 under E-V. Echoic decision time under V-E averaged only 1.88 s. Experiment 2 tested 4 new pairs of objects for 24 trials of V-E and 24 trials of E-V without any prior exposure of these objects. Two pairs yielded performance significantly above chance in both V-E and E-V. Also, the dolphin matched correctly on 7 of 8 1st trials with these pairs. The results support a capacity for direct echoic perception of object shape by this species and demonstrate that prior object exposure is not required for spontaneous cross-modal recognition.

Receptive competencies of language-trained animals

Publisher Summary The chapter discusses on what is known of the receptive competencies of animals in language like tasks. The emphasis is on the extensive work with apes, as well as the recent work with marine mammals, bottle-nosed dolphins. Sign language projects have given little attention to receptive competencies. Generally, data from these studies are insufficient for judging the degree to which apes understand the signs of their trainers. The most extensive attempt to quantify sentence comprehension in apes was that by Premack. The chimps Sarah, Peony, and Elizabeth were tutored in a system in which plastic symbols of arbitrary shape and color were used to represent objects, properties, and actions within an artificial language. Sentences could be constructed, by the experimenter or by the chimp, by arranging the symbols in a linear array on a board. There is evidence for an asymmetry of comprehension and production in the development and maintenance of language in humans. During early childhood, comprehension generally precedes and exceeds production. The ability of dolphins to understand imperative and interrogative sentences expressed within artificial acoustic or gestural languages is examined. Two young female bottle-nosed dolphins (Tursiops truncatus), housed together in a large seawater tank, were tutored in the artificial languages.