Page 49 - Spring 2019
P. 49

led Earl to suggest that Heptuna (and by extension other dol- ery possible way to station on the vertical bite plate just as he
phins) had the abilityto focus his echolocation attention on a had before on the horizontal bite plate except turning on his
segment of time that encompassed the returning target echo, side. This was perplexing because this was a behavior that
allowing the dolphin to ignore sounds before and after the Donna McDonald had used in her study (it was found later
echo (Murchison, 1980). that he twisted in the opposite direction for Donna). The is-
When Earl finished his range resolution studies, Heptuna be- sue_was overafrfje by slowly r_°mtmg_fl_le hm Flam from ‘_he
. . . horizontal position to the vertical position over several train-
came available for other research. Whit Au wanted to contin- _ _ _
, . . . . . mg sessions and then Heptuna started the vertical measure-
ue to explore Heptunas hearing abilities. Because Whit and _ _
. . . merits. From these data, it was possible to compute Heptu-
Patrick Moore had worked together on earlier experu-nents , _ _ _ _ _ _ _
. . . . . nas directivity index and model a matched pair of receiving
involving sea lion sound source localization (Moore and Au, _ _ _ _
. . transducers that had the same directivity as the animal. Two
1975), they teamed with Heptuna to better understand his _ _
. . . . . . major observations of the beam patterns were that as the fre-
hearing using receiving models from classic sonar acoustics. _ _ _

. . . quency increased, the receiving beam became more narrow
This began a multiyear research effort to characterize Heptu- < _ H uh f d _ th b ‘ C d M__ H
nas hearing (e.g., Moore and Au, 1983; Au and Moore, 1984; 2:15:11 air‘: ‘ $35 o“_n_ mb e 3 ’ aspekisban d u 6:
Bmnsmter 6‘ 31” 2007) ) an a e receiving eam was muc roa er an

overlapped with the transmit beam (Au and Moore, 1984).
The first task was to collect masked hearing thresholds at un-
explored high frequencies and compute critical ratios and Heptuna and l:anI'.rallad Enhulocatiun
critical bands (Moore and Au, 1983). Armed with these data, Moore’s observations over several echolocation experiments
it was possible to start a series of experi.ments to measure Hep- found a wide variation in clicks, some with a high source
tunas horizontal- and vertical-receivmg beam patterns (Au level but with a lower frequency and vice versa. The ques-
and Moore, 1984). This was the first attempt to quantify the tion became, “does the dolphin have conscious control over
receiving beam pattern for an echolocating marine mammal. click content?” Can he change both the level and frequency
The investigators used a special pen with a 3.5-meter arc that of the click as needed to solve an echolocation problem or is
filled two sides of a 9-square-meter pen. Heptuna stationed at it a fixed system so that as the dolphin increases the level, the
the origin of the arc on a bite plate and was required to remain peak frequency also increases?
steady during 3 mal‘ Hjavmg Hepmm 5'“ fife bus Flam  Again, Heptuna was chosen to help answer this question.
easy as this was something he had done in earlier studies using . . . . .
_ _ _ _ _ This began a very difficult and long experiment involving
a chin cup. Still, having Heptuna transition to the new 1.5-me- . . . .
_ echolocation. Heptuna took part in a series of experu-nents
ter depth of the bite plate proved to be a challenge. Heptuna . . . . .
_ _ _ _ designed to tease out if the dolphin actually had cognitive
did not like the aluminum pole used to suspend the bite plate . .

_ _ _ _ _ _ control over the fine structure of the emitted click. Dr. Ron-
above his head to hold it in position for the horizontal mea- ald Schuster had ahead demonsmned tonal Comm]
suremenm Wild-born dolphins avoid filings over their heads’ over a dolphin’s echolocation Zlick emission Schusterman et
which is why it is necessary to train them to swim through . . '

_ al. (1980) trained a dolphin to echolocate on a target only
underwmer gmes with overhead supports‘ when a tone stimulus was present and to remain silent when
Once Heptuna was satisfied that the overhead pole was not it was not. This experiment started with the attempt to place
going to attack him, the experiment began. The arc in the both Heptunas echolocation click source level and frequency
pen allowed positioning of the signal source about Heptunas content under stimulus control while he was actively detect-
location in 5’ increments. For the horizontal beam measure- mg a target echo.
méms’1_tYofimat;hledhnols: sgmices were placed 1:20 m ‘:6 Heptuna had to learn to station on a bite plate and then place
a_mma S C an n_g t an ‘ C mVe?Ugamrs Co“, m°_ve  6 his tail on a tail rest bar behind him, close to his fluke. This
signal source. During all of the testing, Heptunas stationing mmoning Procedure was necessary ‘O ensure ‘hat Hepmm
was monitored by an overhead television camera to ensure was “able and an ned Wm] ‘he C1iCk_reCeivin h dmphone
he was correctly stationed and unmoving. . . g . . . g Y .)

ensuring on-axis sampling of his clicks. Heptuna found this

After data acquisition for the horizontal beam was finished, new positioning not at all to his liking. And much like the
Heptuna moved to the vertical beam for measurements. vertical bite plate with the beam pattern measurements issue
Again, Heptuna proved to be a dolphin of habit. He tried ev- mentioned in Heptuna and Echolocation Studies, Heptuna
Spring 2019 | Annuslzlcl Tnduy | 47

   47   48   49   50   51