1. Measuring Underwater Hearing in Diving Birds
Jennifer James, NUWCDIV NPT
Heather Hopkins, NUWCDIVNPT
Sara Crowell, I.M. Systems Group, Inc.
Alicia M. Berlin, USGS PWRC
Jonathan Fiely, Cornell Laboratory of Ornithology
Glenn H. Olsen, USGS PWRC

2. Underwater Hearing in Birds
Auditory Brainstem Response (ABR)
Electrophysiological method to test hearing
Subdermal electrodes are used to observe a scalp-recorded potential representing large population neural responses occurring along the auditory nerve and auditory brainstem nuclei, as the bird hears sounds played from an underwater sound source.
Time-efficient, minimally invasive technique
ABR measurements recorded within an hour.
Birds are anesthetized, intubated, and suspended underwater on a platform during ABR tests.

3. Background Test Location
ABR occurs at the USGSs Patuxent Wildlife Research Center in Maryland
Houses active research colony of 150 individuals of 9 bird species; 7 of which are diving species
Harlequin duck, surf scoter, white-winged scoter, black scoter, common eider, long-tailed duck, lesser scaup.
Two large dive tanks (2.4 m x 1.8 m x 2.4 m; 7,571 liter capacity).

4. Dive tank with suspension platform
Dive tank with suspension platform. During ABR testing, individual seabirds are suspended from the platform and lowered underwater.

5. Subjects – Surf Scoters
4 adult male surf scoters (Melanitta perspicillata) – captive raised from eggs.
Chosen because of their participation in other hearing studies at PWRC.
2 of the 4 have been part of ongoing behavioral hearing tests.
Allowed for direct comparison of audiograms resulting from ABR and behavioral examinations.

6. Experimental Design Concrete tanks
Ducks tested at approximately 2.5 m deep
Acoustic source centrally located
General ABR procedures followed
Ducks were sedated and then intubated by on-staff veterinarian
Stabilized prior to submersion in the tank
Ducks were stabilized on platform for submersion
Breathing for ducks was maintained throughout the experiment while heart rate was also monitored

7. Details
Ducks were presented stimuli made up of tone bursts (very short tones).
Tone burst frequencies were 500, 1000 and 2,000 Hz, with pressure ranges from 105 to 145 dB re 1 µPa.
Each set was composed of a pulse train of nine single frequencies tone bursts that increased successively in pressure and were presented at a rate of 4/s.
Each ABR represents an average response of 600 stimulus train presentations.

8. Results
Peaks for ABRs within the first 5 ms of the stimulus reaching the bird’s ear canal.
Peak sensitivity was 1,000 Hz with an average threshold of dB re 1 µPa.
While only 3 frequencies tested, data suggests the likelihood of a U-shaped audiogram found in the in-air ABR audiogram of the same species and the underwater behavioral audiogram.

9. Results

10. Discussion
3 frequencies were tested, the average Surf Scoter underwater ABR audiogram suggests a U-shape common to Surf Scoters and other bird species tested in-air using both ABR and behavioral methods (Crowell et al., 2015; Crowell et al., 2016) and underwater (unpublished data, McGrew, 2017).
Sensitivity peaks at 1,000Hz with an absolute average threshold of dB re 1 µPa. Average ABR thresholds were higher then behavioral.
Disparity most likely attributed to a variety of factors including stimulus characteristics, physiological state of the ducks and other differences in the nature of the two methods.

11. Special Thanks! U.S. Fleet Forces – Hank Eacho, Laura Busch
NUWC Newport – Joe Iafrate, Matt Gilchrest

12. QUESTIONS???