Crocodilian Communication
A. mississippiensis hatching call

The first sounds that an alligator makes are just before hatching - from within the egg. These "hatching calls" continue after hatching and they trigger parental care behaviour in the adults.


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
HATCHING CALL
(post-hatching, 3 calls)
8-bit
16.3 k
16-bit
65.0 k
0.76 s
Spectrogram

Power spectrum The spectrogram (above) shows the first two hatching calls you can hear in the sequence. The spectral structure of these calls is distinct - a concave, frequency modulated (i.e. changing frequency) downsweep. This means that the frequency decreases from the start to the end of the call, and the rate of change decreases as the call progresses. Each call comprises the fundamental and several detectable harmonics. The maximum energy of the call is not necessarily in the fundamental harmonic, as you can see in the second call.

The power spectra show the first (a) and second (b) of these calls, and show peak frequencies at 1.16 kHz and 0.90 kHz respectively.

I divide hatching calls into those produced before hatching (pre-hatching) and those produced after the hatchlings starts to emerge from the egg (post-hatching). There are some spectral differences between these calls (as perceived by the listener), and it may be possible that they play slightly different roles. The calls shown here are post-hatching calls. They are produced when the crocodile is in the process of emerging from the egg, and for several minutes after hatching. Their role is to attract the parent (which is normally the female, but may be the male in some species) and trigger "parental care" behaviour (opening the nest, picking up the hatchlings, transporting them to the water). They also have an effect on conspecifics, causing them to stay relatively close to one another (creating a creche or a pod). Spectrally, these calls may be indistinguishable from "contact calls", but in the context in which they are produced, they trigger a different behaviour from the adult crocodiles.

Hatching calls are normally produced when the mouth is shut. If the mouth is open, the palatal valve appears to be shut in most cases. The crocodile does not appear to assume a particular posture during call production.

If you were to translate this call, it would mean "Mum! Dad! Here I am! Come and protect me!"


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