Date of Award

Spring 2019

Degree Type


Degree Name

Doctor of Philosophy (PhD)



Committee Chair

Alen Hajnal

Committee Chair School


Committee Member 2

Heidi Lyn

Committee Member 2 School


Committee Member 3

Richard Mohn

Committee Member 3 School


Committee Member 4

Jason Mulsow

Committee Member 5

Mark Xitco


As human populations rise, the level of man-made noise increases globally. Naval sonar and boat traffic are underwater sound sources of particular concern to marine mammal welfare. To better understand the impact of these noise increases on cetaceans, studies can explore animals’ behavioral changes in response to noise. Studies have investigated the ‘dose-response’ relationship between the received sound pressure level of sonar signals and the behavior of cetaceans in the wild, but exposure studies in controlled environments are limited. The studies in this dissertation examined bottlenose dolphin vocal modifications during various experimental noise treatments. Acoustic recordings previously obtained for bottlenose dolphins (Tursiops truncatus) exposed to simulated (1 s, 3.25–3.45 kHz) sonar signals (Houser et al. 2013) were analyzed in Experiment I. Thirty dolphins were trained to swim across an enclosure, touch a paddle, and return to the starting location. Each dolphin was placed into one of six groups which received a single sonar “ping” exposure of 115, 130, 145, 160, 175 or 185 dB re 1 μPawhile crossing the midpoint of the enclosure on exposure trials. Dolphins produced fewer whistles in exposure trials except at the highest received level (185 dB re 1 μPa) where more whistles and higher whistle repetition rates occurred. Dolphin vocalizations mirrored previously reported behavioral responses from Houser et al. (2013) in that vocal displays and behavior varied with increasing received level. This suggests that dolphins show a differential vocal response to varying levels of simulated mid-frequency sonar exposure, with the most dramatic changes occurring at the received SPL where trained behaviors are abandoned.

Experiment II examined the vocal modifications of three dolphins (ages 30-52) used in the presence of experimentally controlled background noise conditions. Behavioral hearing tests using an adaptive up-down staircase, go/no-go procedure emitted 40-kHz tones which dolphins responded to with a conditioned whistle. Dolphins performed this task in San Diego Bay during ambient noise (control) conditions, as well as three elevated bandpass noise (experimental) conditions: 0.6-5 kHz (125 dB re 1 μPa, mean 1/3-octave band level) and 0.6-10 kHz (115 and 125 dB re 1 μPa, mean 1/3-octave band levels). The acoustic parameters of the dolphins’ response whistles and burst pulses were analyzed, and provided examples of the Lombard effect in both whistles and burst pulses, as well as increases in whistle harmonics and highest frequency present. These results fill a gap in basic research and complement field studies of odontocete noise-induced vocal modifications in the wild.