The call of the penguin is a curious sound. It can range from the gentlest peep to a most unbecoming squawk. And yet, they appear to use the same vocal patterns as humans, researchers have revealed; the first non-primates found to do so.
Researchers studying the display songs of African penguins in captivity found that penguins communicate in the most efficient way using shorter sounds for the “words” they use most often and longer vocalizations with more syllables for more complex messages – both of which adhere to two linguistic principles found in human speech around the world.
The first, known as Zipf’s Law of Brevity postulates that the more frequently a word is used, the shorter it will be, and vice versa. This can be found in languages around the globe – yes and no are good examples, as are warning words like help, or fire. It’s thought information compression is a general rule that applies to all human language, due to selective pressures to communicate accurately but efficiently.
The second principle, Menzerath–Altmann Law, says the longer a word or sentence, the shorter the components in it, ie a complex word like "discombobulate" has shorter syllables compared to a simpler one-syllable word like "screeched".
Both principles have been documented in the vocalizations of non-human primates. However, “Our results provide the first evidence for conformity to Zipf’s and Menzerath–Altmann Laws in the vocal sequences of a non-primate species,” the study authors write in Biology Letters.
To discover this they studied the display calls of 28 adult African penguins – knowns as jackass penguins due to their donkey-like bray rather than their tendency to be a jerk – in three colonies in Italian zoos.
They collected and analyzed 590 “ecstatic display songs” (their words, not mine) during the 2016-2017 breeding season. These calls, usually uttered by males, signify their suitability as a mate, claim territory by warning off usurpers, and identify themselves as individuals to their comrades.
The researchers found that the songs were made up of sequences of three distinct sounds. The first two, a short croak lasting just 0.18 seconds, and a longer noise made when exhaling that lasted for 1.14 seconds, were the most and least used. The third, made when the birds breathe in, varied in length depending on lung capacity, but averaged 0.38 seconds long. The researchers think this one particularly demonstrated to mates they were the fitter prospective partner. Sort of like the penguin version of trying to impress a love interest with fancy words.
“As predicted, we found that the duration of the syllables was inversely correlated with the frequency of occurrence,” the researchers write, confirming the first documented case of non-primates using this complex linguistic behavior.
Although the researchers are quick to note that this study only looked at one form of vocalization in one species of penguin, they think it goes towards evidence that language laws are not intrinsically about the semantics and syntax, but are more about the fundamental principle of communicating information efficiently.
That they have been observed in non-primates suggests that “these laws can co-exist with other selective pressures specific to a species’ ecology,” meaning they probably occur in other animals, we just haven't documented it yet.