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Penguins have long been studied for the way they behave in colonies, their mating patterns and relationships.

But their squawks and calls have only ever been identified at a basic level.

For the first time, researchers in Italy studied 48 African penguins to not only discover they make six distinct calls – they were also able to identify these sounds in context.

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Researchers from Italy studied the vocalisations of African penguins (pictured). This included 32 adults and 16 chicks at Zoom zoo in Torino, Italy. They discovered four distinct calls in adults, and two in chicks, including display songs, contact calls and begging 'peeps' and moans

The researchers, led by Dr Livio Favaro from the University of Turin, collected, categorised, and acoustically analysed hundreds of audio and video vocal recordings.

All were taken from a captive colony of 48 penguins at the Zoom zoo in Torino, Italy.

This group was made up of 15 males, 17 females, eight juveniles aged between three and 12 months, and eight nesting chicks.

The results revealed that all the penguins have four essential vocalisations: a contact call emitted by isolated birds, an agonistic call used to signal aggression, an ecstatic display song uttered by single birds during the breeding season, and a mutual display song made by pairs at their nests.

The authors also identified two distinct vocalisations interpreted as begging calls by chicks, in the form of a begging 'peep', and a begging moan.

Secret language of penguins revealed

The results revealed four basic vocalisations: a contact call emitted by isolated birds, an agonistic call used during aggression, an ecstatic display song used during breeding, and a mutual display song made by pairs at their nests. The authors also identified a begging 'peep' and moan among the chicks

'The African penguin is a highly social and vocal seabird. However, currently available descriptions of the vocal repertoire of African Penguin are mostly limited to basic descriptions of calls,' said the researchers in the journal PLOS One.

'Here we provide, for the first time, a detailed description of the vocal behaviour of this species by collecting audio and video recordings from a large captive colony.

'Establishing a comprehensive classification of bird vocalisations is important, it allows comparisons between species and individuals, and also contributes to planning effective management and conservation strategies.

'Indeed, vocalisations have the potential to provide a variety of information about bird sex, age, behavioural state, condition, and relationships with surrounding animals.'

THE SECRET LANGUAGE OF THE AFRICAN PENGUINS 

Contact call

The contact call is a short call consisting of a single sound.

The vocalisation has a clear harmonic structure and during the call, the beak is half-open and the bird stands up, extending the neck upwards as much as possible. 

It is made by chicks and adults of both sexes.

Agonistic call

Similar to the contact call, the agonistic call is a short single utterance that shows a clear harmonic structure. 

During the call, the birds stand up and extend the neck towards the recipient of the aggression.

Ecstatic display song

The ecstatic display song is the longest and loudest vocalisation.

Penguins make this sound resting with their feet apart, their neck and beak facing upward, and their wings positioned horizontally. 

The song is composed of a sequence of vocal syllables combined in a phrase.

It begins with a sequence of short syllables during which the keeled sternum moves upwards and downwards and culminates with the emission of a long syllable during which the sternum remains upwards.

These spectrums reveal the different vocalisations. Contact call is shown at (a), agonistic call (b), ecstatic display song (c: arrows indicate short initial syllables 1, longest syllable 2, inspiration syllable 3), mutual display song (d), begging moan (e), begging peep (f)

Mutual display song

This call begins with pulsed noises and ends with a clear low-pitched harmonic structure.

All the while, the penguin's body is horizontal, the neck is extended as much as possible, and the beak is wide open.

Begging moan

The begging moan was only emitted by juveniles and featured a clear harmonic structure and a short duration. 

Juvenile penguins emitted long sequences of one to 10 begging moans, but they immediately stopped calling when they were fed, or when the parent moved away. 

During the calls, juveniles performed quick lateral movement with their heads.

Begging peep 

The peep is a begging call emitted by chicks inside the nest. 

The average duration of a single peep recorded in this study was only 0.36 seconds but this call was repeated by chicks in long sequences lasting for several minutes, until they were fed. 

The peep is a high-pitched vocalisation, up to 17 kHz. 

The calls are made through what's called the syrinx, which differs from the mammalian larynx.

In particular, the syrinx is at the base of the trachea, while the mammalian larynx sits above it.

The syrinx is made of two parts - an independent set of muscles, and membranes at the right and left sides.

Unlike mammalian vocal folds, this means many birds, including penguins, can produce two independent signals at the same time. 

Since the colony is captive, the authors said they can't be sure they've identified all possible vocalisations, but suggest this analysis helps to standardise the known sounds.

This chart reveals the six distinctive sounds recorded from the penguin colony. It plots where they sit in terms of discriminant function analysis (DFA). DFA is a statistical way of grouping objects together and predicting patterns. The mutual display song, agnostic call and begging moan overlap, but the begging peep is distinctive