Friday, May 27, 2016

How hyenas use whoops to communicate

Communication: The whoop.

If you were asked to define communication, what would you say?
You might think it is an obvious subject to define; I talk and you listen. You may also recognize that within the animal kingdom there are numerous ways to communicate and therefore, it can be difficult to find one definition that includes all the modes of communication between species. Here I would like to define communication and explain how animals, like hyenas, do so.

Communication is defined as a signal being sent from one individual (sender) and received by another individual (receiver). The signal has some sort of information within it and the receiver uses that information to make a decision.

Signals can take many forms (i.e visual, acoustic, chemical, auto-communication) and signals can carry different types of information the sender wants the receiver to know. A signal is made by the sender in order to affect the receiver’s behavior in some way.
Signals that have been favored by selection elicit a response from the receiver that most likely benefits the sender while indirectly or directly benefiting the receiver.

For example, what does it mean when your mother glares at you for sticking your hand in the cookie jar before dinner. The glare is a visual signal sent from your mother across the room to be received by you, when your eyes become locked onto hers. Most of us know exactly what she means without a sound coming out of her mouth. The information the glare carries is “Don’t you dare take a cookie out of the cookie jar!” 

In addition to signals taking visual form they also can take acoustic or sound form. We all can think of a moment when an animal makes some sound or vocalization that we have perceived as having some sort of meaning. When my dog needs to go outside, like the good boy he is, he whines at me. I perceive that he is trying to get my attention and tell me something. The vocalization he makes is a signal to tell me he wants to go outside and I am going to make a decision either to let him out or not.

It’s interesting to think that if I can interpret what my dog is trying to tell me, other animals must have ways to communicate certain information with one another. This idea is just one of many questions we investigate in hyenas.

What is sound and how do hyenas use it to communicate?

Like most mammals, hyenas use a combination of signal forms to communicate to each other, but for the purposes of this blog entry I will be focusing on acoustic or sound signals produced by hyenas.

In order to understand how hyenas use sound to communicate, it is important to know how sound functions and the properties of sound. However, I do not think you all want to get a full physics lesson today so I will make a short list of things to review:

1.     Sound is the movement of dense perturbed molecules through a medium away from the initial source.
2.     To create sound an animal has to create a local concentration of molecules denser than the surrounding molecules.
a.      For example, air molecules are less dense than water molecules. This is why you are louder outside of water (easier to create denser molecules) when you scream to the top of your lungs vs when you scream inside of water (harder to create denser molecules).
3.     Sound moves in waves. A wave’s properties include: period (time), frequency or “pitch” (cycle per time; Hz), amplitude or “loudness” (height of wave), phase and wavelength.
4.     Sound responds to changes in pressure.
5.     Sound propagates at different speeds through air, water and solids, and can be impeded by the matter it moves through.

It is also important to know sound is produced.
Sound is produced by three steps:

1.     Creating Vibrations
2.     Modifying Vibrations
3.     Coupling Sound

Most mammals use their larynx to produce sound. Animals make vibrations either through muscular contractions, stridulation (i.e. crickets), percussion or forced flow of medium through small opening. The vibration then is filtered by an internal mechanism or constraint which results in the modified signal. The modified signal is sent out and must be coupled or matched properly to the animal’s environment. Coupling or matching depends on the morphology and internal mechanisms the animal uses to produce its vibrations.

Receivers of the sound also have to couple, modify and analyze the information given to them before making a decision. 

Hyena Sounds

Hyenas produce many different vocalizations. Some include:
The giggle or most commonly known as a hyena "laugh." The groan, which is a low humming sound. The growl, like how your dog may growl. The low, sounds like the mooing of cattle. And the whoop, a long distance sound compiled of high and low frequency notes.

The whoop is a powerfully unique sound not found in any other mammalian species.  For this reason, and many others, the whoop vocalization has been a target for research. 

Historically, researchers have investigated the whoop vocal structure, as well as, the whoop’s behavioral functions (East & Hofer, 1991). Hyenas display their own identify through their whoops. The literature provides evidence to hyena’s abilities in recognizing individuals by their whoops. They also discuss how an individual’s whoops remain relatively stable throughout their lifetime but are modified as they mature.
Additionally, researchers have shown whooping is used to broadcast a caller’s location so others can locate her. This function allows callers to defend food resources and territories by rallying allies.

Whoops, as you can see, can communicate various information. This is why our project and graduate student Kenna Lehmann have been working hard to deconstruct the whoop.

Whoop Bout

Within a whoop bout there are three different types of whoops, asymmetrical (A type), symmetrical (S type) and terminal (T type). A whoop bout can combine any of the three types, but are not held to any order.

A type are asymmetrical whoops starting at a low frequency rising to a high frequency with an abrupt fall.

S type are symmetrical whoops starting at a low frequency rising to a high frequency and decline to a low frequency.

T type are terminal whoops; these do not rise in frequency but remain at a constant low frequency. T type are typically heard at the end of a whoop bout.

The recording below illustrates one entire whoop bout.
The whooper is Roswell (RSWL); a tenured immigrant male who reigns over the Pond Lugga group in Talek West clan. He is one of the only males who is allowed to get up close and personal with the females and is speculated of being the sire to many of the cubs in this small group. He begins his bout with a long symmetric (S type) whoop and repeats it 4 times then continues with 2 asymmetric (A type) whoops and ends with a soft terminal whoop (T type). 

When I found RSWL he was sacked on in the road by himself so I decided to stay with him for a while. As I waited he let out this mighty call. Based on the information you have above you may speculate that he was either sending a call to elicit a response from another hyena or letting others know he was around—friend or foe. Regardless, Roswell was definitely announcing his presence and letting all of the Mara know who is Big Daddy.

I hope you have learned a thing of two about whoops and hyena vocalization. I have asked our camp to show our fans a little love and say a little something to encourage people like you to share all you’ve learned about the spotted hyena, crocuta crocuta.

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