Frank T. Awbrey

Low‐frequency underwater hearing sensitivity in belugas, Delphinapterus leucas

The underwater hearing sensitivity of three captive belugas (Delphinapterus leucas) was measured at octave intervals between 125 Hz and 8 kHz. The average threshold of the three animals was 65 dB re:1 μPa at 8 kHz, which is in excellent agreement with previously published data [White et al., HSWRI Tech. Rep. No. 78‐109, Sea World Research Institute, San Diego, CA (1978)]. Below 8 kHz, sensitivity decreased at approximately 11 dB per octave, and was 120.6 dB at 125 Hz.

Natural History Aspects of Marine Mammal Echolocation: Feeding Strategies and Habitat

The state of knowledge of echolocation in marine mammals and cetaceans in particular has been reviewed effectively in recent years (Wood and Evans, 1980; Watkins and Wartzok, 1985). Both of these reviews reveal that most efforts are still directed toward biophysics rather than the natural history, biological, and functional aspects. At the First Animal Sonar Conference in 1966, Donald Griffin and others asked researchers working with cetaceans how echolocation is used in navigation or feeding. Unfortunately 20 years later these two “obvious” uses of this extraordinary capability are still understood mainly by inference. The “Scylla” paradox described in Wood and Evans (1980), indicated that a dolphin deprived of vision can use directional hearing rather than active acoustic scanning to detect and capture moving, avoiding prey. This use of listening (“passive sonar”) has been well studied in bats (Fiedler et al., 1980), but not considered, in print at least, for use by marine mammals. That is changing. Recent tests by Sonafrank, Elsner, and Wartzok (1983) demonstrated that a spotted seal could use vision and listening to find ice holes and to navigate.

Effects of fixed‐wing military aircraft noise on California gnatcatcher reproduction

To test the assumption that high levels of aircraft noise impede bird reproduction, noise analyzers were placed for 1 week in the nesting territory of each of 39 California gnatcatcher pairs on Naval Air Station Miramar. The 1‐week average sound levels (7DL) recorded in those nesting territories were then related to the number of nest attempts; number of eggs laid; number of chicks hatched; number of chicks fledged; and number of eggs, chicks, and fledglings per nest attempt. Nest attempts and eggs laid have weak negative correlations (p=0.14 and 0.28) with 7DL. That is, the birds may tend to build fewer nests and lay fewer eggs in noisier areas, which is consistent with the common observation that bird nesting is more easily disturbed before eggs are laid than after. None of the other indicators is correlated with sound levels. Once a nest is established, with eggs in it, military aircraft noise has no detectable influence on reproductive performance. Gnatcatchers reproduced in places where 1 HL exceeds ...

Concluding Comments on Cetacean Hearing and Echolocation

About forty years ago biologists began to learn that dolphins have an extraordinary ability to use sound to find food and get precise information about their environment. That line of research proved to be very fruitful. Hundreds of studies cover a range of topics from simple descriptions of sounds to complex theoretical models of cetacean echolocation and hearing. The result of all that effort is that we know quite a bit about some aspects of echolocation and hearing in a few odontocete species but almost nothing about it in most cetacean species, especially the mysticetes.

Modeling noise interference with animal communication

Regulators are proposing to set simplistic limits for anthropogenic noise in natural environments. These proposed limits specify only SPL, without regard to the method of measurement, frequency or time weighting, normal ambient levels, or spectra. In some cases such limits may be inadequate, but in others they may be much too severe, resulting in unrealistic restrictions on human activities, including scientific investigations, without real benefit to the animals. Realistic limitations on noise level should incorporate information on the time history and spectrum levels of the noise and the animals’ communication signals, with estimates of hearing threshold curves. This paper outlines an initial effort to devise such a model and to estimate how seriously noise of different kinds will limit communication.

Sonic booms of space shuttles landing at Edwards Air Force Base

At a place 33 miles westerly of Edwards Air Force Base, we measured the sonic boom of Space Shuttle Orbiter STS‐1: a peak flat sound pressure level of 125 dB and a A‐weighted sound exposure level of 81 dB. When STS‐1 was 33 miles distant it was approaching EAFB at Mach 2.6 at an altitude above ground of about 23 km (75 kft); slant range from STS‐1 to the sound measurement position about 25 km. Three miles west of EAFB South Base we measured the sonic boom of Orbiter STS‐9: a peak flat sound pressure level of 131 dB (1.4 psf), a flat sound exposure level of 122 dB, an A‐weighted sound exposure level of 95 dB. The duration of the N wave was 380 ms. Presumably, the boom was generated by STS‐9 decelerating through Mach 1.2, and turning eastward, at an altitude above ground about 16 km (52 kft); slant range south to the sound measurement position was about 28 km (90 kft). We also measured in the vicinity of EAFB for STS‐2, STS‐4, STS‐5, STS‐6, STS‐7, and STS‐8. Dc‐to‐5‐kHz recordings of the later booms provide...

Incidental evidence for echolocation in polar pinnipeds

Efforts to experimentally demonstrate echolocation in California sea lions, Zalophus californianus [W. Evans and R. Haugen, Bull. So. Cal. Acad. Sci. 62, 165–175 (1963); R. J. Schusterman, Psych. Rec. 16, 129–136 (1966)] and in grey seals, Halichoerus grypus [B. Scronce and S. Ridgway, in Animal Sonar Systems, pp. 991–993 (1980)] have been unsuccessful. However, similar studies on polar pinnipeds have not been conducted previously. No studies have investigated the potential for ultrasonic vocalizations in pinnipeds. Echolocation in polar pinnipeds has been suggested because of their highly developed vocal abilities and their need to find food and navigate during the dark austral winter [G. Kooyman, Ant. Res. Ser. 11, 227–261 (1968); J. Thomas and V. Kuechle, J. Acoust. Soc. Am. 72, 1730–1738 (1982)]. This presentation will summarize observations and evidence that indicates the presence of echolocation in polar pinnipeds and report the production of ultrasonic vocalizations by a captive leopard seal (Hydru...

Are ANSI standards for describing airborne impulses applicable to underwater transients

ANSI standards exist for measuring and assessing airborne impulsive sounds. This paper reviews those standards and considers their applicability and utility in measuring and assessing underwater transient sounds.

Using FFT spectrum analyzers to measure animal sounds

Sound‐pressure levels of animal sounds have been measured in so many different ways that comparison between studies is very nearly impossible. The transient, repetitive nature of most vocalizations means that standard sound level meters may yield very different numbers, depending on meter time constant and frequency weighting. Integrating sound level meters, which average sound over various periods and measure sound exposure level directly, are an improvement, but are hard to use for measuring single, transient sounds such as a frog call or an echolocation pulse. A better way, with brief signals, is to record them through calibrated transducers, along with calibration tones of known amplitude, onto tape recorders with linear response to varying levels. These recordings can then be measured with digital spectrum analyzers in a way that is reliable, accurate, and repeatable. Possible measures include peak, octave, one‐third octave, maximum, time‐average, sound exposure, and spectrum levels. Comparability re...

Sonic boom spectra of Atlantis landing 6 December 1988

After circling the world 69 times, orbiter Atlantis came to a stop on Runway 17 of Edwards Air Force Base in California, at 1537U on 6 December 1988. Some 10 mi to the west, and 4 min previous to landing, its 394‐ms sonic boom swept over our measurement site at latitude 34.886°N, longitude 118.036°W, elevation about 2.5 kf above sea level. When the decelerating Atlantis heading southeast passed nearest to the microphones at lateral slant range of 100 kft, it was gliding at Mach 1 about 48 kft above ground. The peak flat sound pressure level of the sonic boom was 129 dB; the peak C‐weighted sound pressure level, 125 dB; the peak A‐weighted sound pressure level, 110 dB. The flat sound exposure level was 118 dB; the C‐weighted and A‐weighted sound exposure levels of the initial transients were, respectively, 102 and 84 dB. If sound exposure level is wanted for a 400‐ms sonic boom with primary emphasis in the range 0.8–3 Hz, flat sound exposure level is appropriate; with primary emphasis in the range 10–50 Hz...