Animal Myths I Believed: Marine Mammal Hearing Range Edition

There are a few things that I've heard during my time as a marine mammals trainer that have turned out to be well, not so correct.   To be honest, this piece of information has almost reached Myth Status in my mind.

Animal myths are where it's at!

Now before anyone gets a little irked, let's remember something important here: the study of the natural world is progressive.  What we take for granted as fact today may very well not be fact tomorrow.  In some cases, this seems really unlikely (the theory of gravity*, for example).  In others, we can expect to see some big changes, like in the medical field.

The better our technology gets, the better our scientific understanding becomes.  For example, I learned from a helpful commenter on one of my blogs that skunks are no longer considered mustelids.  When did this distinction change?  In 2006, thanks to our ability nowadays to do observe cool stuff at a molecular level.  Turns out, skunks are currently the sole member of Mephitidae.  

Mephitidae, mustelidae....I say we have a Cuteidae family and we can lump lots of critters into it.

So when I say there are things I learned as a marine mammal trainer that turn out not to be true, that's not a knock on anyone.  It may be information that was simply not updated, because the scientific world changes rapidly at times.  ESPECIALLY when it comes to animals.

I've already addressed some of these Myths of sorts (like this blog about anthropomorphism and  animals having emotions, and the fact there are literally hundreds of empirical studies supporting that non-human animals have emotional responses).  But the one I'm talking about...well, you've probably heard some version of this one:

"Dolphins can't hear human voices clearly."

I'm a tad deaf in this ear, speak with a little higher frequency.

Some people have gone as far to say, "Our voices sound like Charlie Brown's teacher."

You know, Charlie Brown's teacher with the "wah womp wahhh womp wah wah" voice, ala muted trumpet sound.

Trumpet mutes?  Or technological advancement in interspecies communication between  H. sapiens and T. truncatus?

When I first heard this, about the fact that dolphins could not hear human voices very well, I believed it.  For those of you readers who are not in the zoological industry and/or who enjoy being hyper critical of people in my profession, let's just get something straight.  I don't just blindly accept what people tell me as truth. I spent a good number of years studying animal (especially cetacean) behavior and physiology.  I could tell you about the structure of a cetacean eye (including translating a paper on dolphin retinas  from Russian to English), the differences between social structures in different species of dolphins, or every Latin name for every dolphin species found on this planet.  My understanding of their hearing range was limited to knowing their upper hearing threshold was around 150kHz.  

I just had no clue what the human vocal range was.

So when someone said, "Hey, dolphins can't really hear you talking.  Or at least not that well," that made sense to me.  They have an insane range of hearing, well above what humans can hear.  They also seem to super compress acoustic information; what sounds like one whistle to us may in fact be many whistles happening simultaneously or in quick succession, but our brains cannot process this information the way a dolphin brain can.

The only thing I didn't understand is how anyone knew that we sounded like Charlie Brown's teacher with the unfortunate voice.  Did we ask the dolphins?  Like Carl Sagan's Voyager, drifting into space with a Golden Record to play sounds of mankind to life in other galaxies, did Jacques Cousteau send down a submarine filled with pop culture references so that the alien world of the ocean could know A Charlie Brown Christmas?  

Surely the dolphin hearing range encompasses a low enough frequency to enjoy  the incredible piano compositions of the Vince Guaraldi trio.

In all seriousness though, are we assuming something about dolphins that maybe isn't true?

Going further, how many pinniped trainers out there have heard that the reason we use verbal SDs with them is because they can hear us well, like a dog?  I heard that, and it also made logical sense to me.  So many facilities use verbal SDs with their sea lions, seals, fur seals, and walruses.  And let's be honest, there are a few of us who have been a little sassy when we've heard of some facilities using verbal SDs with their dolphins.  I remember hearing a former trainer tell me that they "didn't believe" that it was possible to really train a dolphin on audible SDs; that a sort of Clever Hans thing** was happening.  

You so clever.

Well guess what.  It's time to clear the air.  Get ready because here's the answer:

Dolphins can hear our voices. Yep.  And dolphins can absolutely be trained using verbal SDs.  In fact, the first trained bottlenose dolphin in the 1950s was conditioned on verbal cues, because that was the traditional method of animal training back then.  And it's successfully done currently at other facilities.

I can hearrrrr youuuuuuuuuu

Let's look at some science though, just in case you think I'm crazy.

The hearing range of a bottlenose dolphin is:

75 Hz to 150kHz

It's one of the largest hearing ranges in the animal kingdom.  

What does 75 Hz sound like?  Here you go:

Low, huh?

What's a normal vocal range for a human being's voice?  Unless you're some kind of sexy dude like Kevin Richardson from the Backstreet Boys (oh godddd his voice), the average tone for an adult male is 125 Hz, and for females it's around 200 Hz.  That range falls well into the hearing range of a bottlenose dolphin.  Fact fact fact.

Baby, you know I'm hurting'.  But looking at you right now I feel like I could love again

Does that mean we sound muddled or unclear?  Who knows?  I mean, unless someone's asked them that question.

As an aside, one of my fears is talking to a dolphin and having a conversation like this:

Me: Wow, Alvin, this is a real honor to get to talk to you.  This conversation will be the absolute best day of my life.  

Alvin:  I'm sorry, what? I can't understand you, you sound like a muted trumpet.

Where does that leave our friends the California sea lions?  What's their hearing range, considering many of us are told as trainers that the sea lions can hear us "better" than the dolphins?

As of right now, the most acute underwater hearing range is:

0.4 kHz to 32 kHz.   And there is evidence in one study animal that she could hear down to 0.1 kHz.  That's 100 Hz.  ***

With more auditory research, we could find out that in fact sea lions DO hear lower tones than dolphins, but as of right now, they still do not seem to hear frequencies as low as bottlenose dolphins.  And that's just how well they hear underwater.   The general consensus is that hearing ability becomes lesser in air for seals and sea lions, but that tends to deal with the higher frequencies versus the lower ones.  

Marine mammals of the world unite in your ability to hear the naked apes of the Earth!

Does that mean to sea lions, we sound like we have socks stuffed in our mouths?  I don't know, but we've collectively decided that sea lions can hear us better than dolphins, so we train them with our voices.  And we assume for some reason that dolphins cannot hear us, so we train them using SDs that are not out voices.  And some of us mistakenly criticize other facilities who do use verbal cues.  Hmmm.

What's the point of this blog then?  It's not to make us feel sheepish or bad.  It's simply to be like hey trainers (myself included!!!!!!), let's remember that it's a good idea to continuously read up on our field, and not just about training.  We are so good about this when it comes to providing great quality of life for our animals.  If using verbal SDs was a critical quality of life topic, I have no doubt this myth would not have gained ground.  Plus, most of us (even those of us who say they can't hear us) talk to the dolphins incessantly.  There is no lack of social interaction and lots of gooshy love going around.  But when it comes to stuff that is just interesting, I think many of us (again...can you see me raising my hand and saying, "ME TOO!") get stuck in this "well this is how it is" instead of thinking more scientifically: Is this how it is?  What about this? What about that?  What's the latest information on this topic?  How often do I read new published articles on the animals in my care?  Or talk to people who like to read that stuff?

Hey look, if Al said it, we should probably take it seriously.

Also, embrace learning something new, even if it meant you were mistaken before.  Being right all the time is impossible.  And in a scientific field, you can't afford to be set in your ways.   Plus, it may mean that you can really expand your training program's variability.  And let's be honest, for us Animal Lovers, isn't it nice to know that all of those lovely compliments you give your dolphins every day aren't falling on deaf ears? :)


________
* Yup, it's a theory.  If you thought it was a law, technically that is the Law of Gravitation, which is the computational element of gravity (e.g. you can calculate the gravitational pull of the Earth).  The theory of gravity describes WHY objects are attracted to each other.  Semantics, really.  But boy do I love words.

** Clever Hans was a horse who was trained to tap out answers to math problems with his hoof.  Upon further investigation, it turned out Clever Hans was watching the person asking him the questions carefully; if the questioner knew the correct answer, Clever Hans picked up on some very subtle cue that told him when to STOP tapping his hoof, "correctly" answering the question 89% of the time.  If the questioner didn't know the answer to the problem, Clever Hans only got the answers right 6% of the time.

*** I research lots of these things, but this is a laid back blog that I don't feel requires me to cite references in order to prove a point (although I want to give credit!).  But!  This is a really great article:  http://pinnipedlab.ucsc.edu/publications/pub_146_2011.pdf