Acoustic features of long-distance calls of wild cheetahs (Acinonyx jubatus) are linked to the caller age from newborns to adults

Wild cheetahs Acinonyx jubatus of all age classes, from newborns to adults, use their long-distance chirps for communication with conspecifics. We investigated the ontogenetic changes of eight acoustic parameters of the chirps produced by wild-living cheetahs across 14 age classes in Kenya. Chirp maximum fundamental frequency (f0max) was found to be best acoustic correlate of cheetah age. The f0max was the highest in neonates (up to 10 kHz), then decreased steadily across age classes and reached a plateau of about 1 kHz in mature adults older than 4 years. Based on a close relationship of f0max with age, we fitted polynomial models for estimating cheetah age by their chirps. We discuss that gradual changes of chirp f0max suggest the gradual development of cheetah vocal apparatus. Model for age estimation by chirps in the cheetah proposed in this study may provide conservationists a non-invasive bioacoustic tool for estimating cheetah age, particularly at ages younger than 4 years. However, introducing more data from cheetahs of precisely known age would be necessary for obtaining more accurate results of age determination by voice for the older individuals.