Crocodilian Communication
A. mississippiensis threat call

When an alligator doesn't want to be disturbed, it may produce a "threat call" when approached. This is one of several kinds of threatening calls produced by a juvenile alligator. Both the spectrogram and the power spectrum of the call are shown below.


Alligator mississippiensis
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To listen to the call which is shown here, click on either 8-bit or 16-bit to download the sounds.


WHAT IT ALL MEANS

The spectrogram to your right shows the sound in a visual form - it plots frequency against time, with intensities shown as different colours. The power spectrum plots frequency against intensity, averaged over the whole call.


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DESCRIPTION QUALITY & SIZE DURATION RELATED CALLS
THREAT CALL
(low intensity hiss)
8-bit
72.3 k
16-bit
289.3 k
3.36 s 1 | 3
Spectrogram

Power spectrum The spectrogram (above) shows a low level threat - a drawn-out hissing.

Although there is little apparent structure to the call, it is divided into two distinct sections. The first is associated with an expiration (breathing out) and, after a short pause, the hiss continues (at 2.0 s) during inspiration (breathing in). In longer hisses, this pattern can continue for several breaths. Notice that the second part of the call, the inspiration, has a lower intensity compared with expiration. The only time that crocodiles makes a noise during inspiration is when they hiss like this. The sound is created by air passing through a constricted opening such as the glottis, nostrils or the even the palatal valve. In the call shown here, it is likely that contraction of the glottal valve is responsible. Although there is no real frequency structure, there are three bandwidths which contain the most energy - these are clearly visible in the first part of the call. The power spectrum shows all three of these quite plainly, the second containing the most sound energy over the entire call (at 3.93 kHz).

This is a "threat call" which, as the name implies, is used against potential threats or aggressors. This hiss variant is produced when the crocodile is starting to feel threatened in some way. During the hiss, the crocodile may also use a number of visual signals to add meaning to the threat - opening the mouth is a very effective signal (exposing the teeth) but other signals include inflating the body, standing up, angling the back and head towards the threat, and twitching the tail. If the nature of the threat persists, then the intensity of the call is increased, and the animal may lunge towards the threat in a bluff or a real biting attack. Alternatively, if the odds are against it, the animal may flee (preferably into water).

If you were to translate this call, it would mean "Come any closer, and I'll attack you."


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