There’s nothing quite like the sultry squawk of a jackass penguin. Coastal residents of Namibia and South Africa, African penguins (Spheniscus demersus) got the nickname “jackass” from their donkey-like calls.
But it turns out their vocalizations are a lot more complicated than haws and brays. A study published today in the journal PLoS ONE examines the vocal repertoire of African penguins. Researchers analyzed hours of audio and video and found that the quirky birds emit four different calls and that baby penguins emit two previously undescribed vocalizations. Perhaps most important, the researchers think they were able to discern what the penguins were trying to communicate with each call.
Understanding penguin call function has implications for conservation and learning about penguin biology. “Vocalizations have the opportunity to provide a huge amount of information about these birds,” says Livio Favaro, a biologist at the University of Turin and the lead author on the study. Encoded in penguin vocal calls are clues to their sex, age and social status.
Before this study, penguins were known to vocalize in four ways: contact calls (“Hey! I’m here. Where are you guys?”), agonistic or threat calls (“Watch it, buddy!”), and display songs directed towards mates, chicks and parents (“Heyyy”). Display songs fall into two categories, ecstatic and mutual, and are uttered alone or in pairs, respectively.
Most penguin vocal research has focused on species that don’t build nests, such as the Emperor and king penguin species in Antarctica, which rely on their vocal system to stick together. By contrast, aside from some basic descriptions and minimal audio, the vocalizations of African penguins—a species that does build nests—remain largely unknown. Previous work also limited the focus to the breeding season, rather than observing the birds over a longer time period.
Favaro and colleagues wanted to know if these nesting penguins voice different calls than their non-nesting cousins. They also sought to discern the accoustic intricacies of different types of calls. But studying penguin vocalizations in the wild can be difficult. Ambient noise, sounds from other animals and human interference can mess with the audio.
So for their study, Favaro and his colleagues selected a captive colony of 48 African penguins living at a zoo in Torino, Italy. For 104 separate days in 2010 and 2011 (both in and out of the breeding season), the researchers took audio and video of the penguins.
Using visualizations of the call notes called spectrograms, the researchers analyzed the acoustics of each call as well as the behavior of the penguin making the call. Based on patterns of behavior and acoustic similarities, four types of adult calls and two new calls unique to penguin chicks emerged from the noise. Statistical analysis of spectrograms confirmed that each call type represented a different vocalization.
You can see video footage of all six calls here:
Contact calls were single-syllable, averaging around half a second in length. When voicing them, penguins typically stood up with their beaks half open and extended their necks vertically as much as possible. When fighting, they extend their necks toward the other penguin and emitted agonistic calls, also one-syllable and sometimes followed by a peck.
Mutual display songs began with noise pulses, and when making them the penguins stretched out horizontally with wide-open beaks while emitting a lower pitched harmony. Finally, the penguins emitted an ecstatic display song, the longest and loudest of all vocalizations. The birds began with a series of short syllables as they thrust their chests upwards with wings spread and ended with one long note, occasionally two.
Both adults and juveniles displayed agonistic calls and contact calls, but penguin chicks emitted some additional calls of their own: begging moans and begging peeps. Begging moans were short, but typically emitted in sequence until fed. The chicks also bobbed their heads. Begging peeps were higher pitched and short, but could go on for several minutes until feeding.
Chicks began emitting begging peeps at three months of age. Moans, which sound more like adult calls, were more common in older chicks. So Favaro thinks that peeps and moans may represent the evolution of the same noise with age.
Understanding penguin lingo could be used to develop audio systems that could provide a cheap and easy way of tracking and estimating populations. From a practical perspective, deciphering penguin audio could prove useful in penguin conservation. The International Union for the Conservation of Nature (IUCN) elevated African penguins to endangered status in 2010, and the birds currently face threats from habitat destruction to pollution and even egg collection.
Such threats put pressure on researchers to learn as much as they can about penguin vocalizations—and how they fit into the broader picture of the evolution of animal communication—before it’s too late.
Favaro and his colleagues next plan to delve into how penguins produce these complex calls through their syrinx, the bird equivalent of the larynx in humans, and how vocalizations identify an individual. In non-nesting species, birds use a two-voice system that creates a beat pattern unique to each individual, while other nesting species, such as the Adelie penguin, use pitch, frequency, and harmony to make unique calls from one penguin to another.
It’s even possible, the researchers suggest, that African penguin speech production follows a theory based on human vocalization that links individuality to variation in the vocal tract. If that proves to be the case, we may be more similar to penguins than we ever imagined.