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Animal vocalisations encode a wide range of biological information about the age, sex, body size, and social status of the emitter. Moreover, vocalisations play a significant role in signalling the identity of the emitter to conspecifics. Recent studies have shown that, in the African penguin (Spheniscus demersus), acoustic cues to individual identity are encoded in the fundamental frequency (F 0 ) and resonance frequencies (formants) of the vocal tract. However, although penguins are known to produce vocalisations where F 0 and formants vary among individuals, it remains to be tested whether the receivers can perceive and use such information in the individual recognition process. In this study, using the Habituation-Dishabituation (HD) paradigm, we tested the hypothesis that penguins perceive and respond to a shift of ± 20% (corresponding to the natural inter-individual variation observed in ex-situ colonies) of F 0 and formant dispersion (ΔF) of species-specific calls. We found that penguins were more likely to look rapidly and for longer at the source of the sound when F 0 and formants of the calls were manipulated, indicating that they could perceive variations of these parameters in the vocal signals. Our findings provide the first experimental evidence that, in the African penguin, listeners can perceive changes in F 0 and formants, which can be used by the receiver as potential cues for the individual discrimination of the emitter., (© 2023. The Author(s).)

The ability to vary the characteristics of one's voice is a critical feature of human communication. Understanding whether and how animals change their calls will provide insights into the evolution of language. We asked to what extent the vocalizations of penguins, a phylogenetically distant species from those capable of explicit vocal learning, are flexible and responsive to their social environment. Using a principal components (PCs) analysis, we reduced 14 vocal parameters of penguin's contact calls to four PCs, each comprising highly correlated parameters and which can be categorized as fundamental frequency, formant frequency, frequency modulation, and amplitude modulation rate and duration. We compared how these differed between individuals with varying degrees of social interactions: same-colony versus different-colony, same colony over 3 years and partners versus non-partners. Our analyses indicate that the more penguins experience each other's calls, the more similar their calls become over time, that vocal convergence requires a long time and relative stability in colony membership, and that partners' unique social bond may affect vocal convergence differently than non-partners. Our results suggest that this implicit form of vocal plasticity is perhaps more widespread across the animal kingdom than previously thought and may be a fundamental capacity of vertebrate vocalization.

Information compression is a general principle of human language: the most frequent words are shorter in length (Zipf's Law of Brevity) and the duration of constituents decreases as the size of the linguistic construct increases (Menzerath-Altmann Law). Vocal sequences of non-human primates have been shown to conform to both these laws, suggesting information compression might be a more general principle. Here, we investigated whether display songs of the African penguin, which mediate recognition, intersexual mate choice and territorial defence, conform with these laws. Display songs are long, loud sequences combining three types of syllables. We found that the shortest type of syllable was the most frequent (with the shortest syllable being repeated stereotypically, potentially favouring signal redundancy in crowded environments). We also found that the average duration of the song's constituents was negatively correlated with the size of the song (a consequence of increasing the relative number of the shortest syllable type, rather than reducing the duration across all syllable types, thus preserving the communication of size-related information in the duration of the longest syllable type). Our results provide the first evidence for conformity to Zipf's and Menzerath-Altmann Laws in the vocal sequences of a non-primate species, indicating that these laws can coexist with selection pressures specific to the species' ecology.

In recent years, awareness of the controversial aspects connected with wild animal-visitor interactions (AVIs) in zoos and other facilities has increased due to cultural changes. Therefore, the need to apply transparent procedures to evaluate AVIs programs in zoos and similar facilities has also increased. This study presents results of animal welfare's assessment of a pilot test of a protocol based on six steps that aim to explore and assess the overall value of AVIs considering the impact both on animals and visitors. In the present paper, we discuss the multifaceted approach to animal welfare assessment during animal-visitor interactions, combining quantitative behavioural observations/analysis and a welfare risk-assessment procedure, which forms the basis of the six-step protocol. Pilot testing of said approach to animal welfare assessment involved giraffes ( Giraffa camelopardalis ) in an Italian zoo. No change in behaviour, suggestive of an increased welfare risk to the animals, was found. The risk analysis reported overall low risks for welfare, whereas enclosure analysis highlighted that the enclosure was suitable for allowing interactions without jeopardising animal welfare, mainly because it allowed animals to choose whether to interact or withdraw from interactions without decreasing the space available to them.

Genealogical relationships among colony members, inbreeding status, and presence of hybrids are crucial data that can assist zoo curators in captive colony management and decision-making on relocation for reproduction. This study employed molecular markers to study a large colony (n = 56) of African Penguin hosted in an Italian biopark. A panel of 15 STRs (single tandem repeats) was selected, and genotype data were analyzed using COLONY software to determine parentage relationships and compare the existing studbook information to a pedigree built from genetic analyses. The existence of extra-pair mating and the presence of hybrids were investigated: discrepancies in kinship relationships emerged following molecular parentage analysis and 10 unknown genetic relationships were revealed. Infidelity of one member of the pair was observed in 6 cases and extra-pair copulation was assessed by genetic analysis in 2 episodes. One member of the colony was found to be a hybrid (S. demersus × S. humboldti); his progeny, derived by extra-pair copulation, was traced. Three other hidden hybrids were discovered and assessed using the identified candidate private alleles. Overall, our results demonstrate that molecular methods to confirm parentage and analyze relatedness among colony members are a valuable tool to complement studbook-based genetic management of African penguin captive populations. Because a variety of behavioral dynamics (e.g., extra-pair mating) can make observations ineffective in some species and because molecular markers outperform studbook in identifying the presence of hybrids, reliance on studbook information alone is not recommended.