Leopard seal song patterns have similar predictability to nursery rhymes.

During their breeding season, male leopard seals (Hydrurga leptonyx) spend hours perfecting their solo performance: singing unique sequences of stereotyped calls underwater to create their 'song'. These song bouts are made up of discrete call types common across leopard seals within a region, which begs the question - what determines the individually unique patterns of these calls? Information entropy quantifies the amount of randomness in a sequence, providing insight into the statistical patterns governing a sequence. The songs produced by 26 different Eastern Antarctic leopard seals have less predictable temporal structure than humpback whale songs and dolphin whistle sequences. The estimated information entropy of the leopard seal songs is comparable to nursery rhymes but unsurprisingly, lower than contemporary, classical and baroque music. The greater structure of the leopard seal's song improves the ability of distant listeners to accurately receive signals and identify singers, which is essential for this widely dispersed species. Future studies examining animal mating song would benefit from incorporating entropy analysis to question if information is conveyed through temporal structure alongside other acoustic variables.