Allometria acustica nei begging calls del pinguino Africano in pre-fledging

Acoustic allometry is the study of biological scaling relationship between animal vocalizations and body size. Vocalizations play a primary role in penguins’ social interactions, as these represent the most important and widely used communication channel. Acoustic allometry in birds, especially in penguins, has been little studied. The African penguin is an endemic seabird species of South Africa listed as endangered since 2010 by the International Union for Conservation the of Nature (IUCN). The purpose of this study was to document the presence of acoustic allometry in the African penguin juveniles hosted at the Nursery department of the Southern African foundation for the conservation of coastal birds (SANCCOB). Specifically, the subjects of this study were 69 penguins weighting more than 1.5 Kg, approximately from 36-45 days-old, to fledging age. Vocalizations were collected from 1st of February to 15th of April 2022. Recordings were made during the facility’s predetermined feeding period with a RØDE semi-directional microphone and a ZOOM H5 digital recorder. A sample of 58 penguins and 510 vocalizations was selected and used in the analysis as they met the selection criteria. The following acoustic parameters were extracted for each vocalization: Sound duration, maximum, minimum, mean, modulation, and time to maximum of the fundamental frequency. A series of Generalised Linear Mixed Effect Models (GLMMs) were built to analyse the relationship between acoustic parameters and the weight of the penguins. The results showed no effect of the weight on any of these acoustic parameters. Accordingly, my findings suggest that there is no acoustic allometry in the African penguin during the pre-fledging phase. The absence of acoustic allometry can be related to the attainment of the final skeletal size and the stability of the membranes of the syrinx. However, further studies are needed to confirm the arrest of skeletal growth at the pre-fledging stage in the African penguin and to better understand how stabilization of the syrinx membranes occurs in the transition between the two phases identified, from the chick weighing less than 1.5 Kg to the pre-fledging chicks in the nursery.