Contextual impacts on individual and synchronous breathing rate variations in three captive odontocete groups

Breathing rates are often collected both in the wild and in captivity to inform on cetaceans' internal state. However, few studies have investigated the effect of various factors on this breathing rate. We investigated the variations of individual and synchronous breathing rates depending on individual features (species, sex, age), displayed behavior, social parameters (social grouping), and environmental parameters (diurnal variation, presence of enrichment, unusual events, and presence of visitors in three groups of captive odontocetes (Yangtze finless porpoises, Neophocaena asiaeorentalis asiaeorientalis, East-Asian finless porpoises, Neophocaena asiaeorentalis sunameri, bottlenose dolphins, Tursiops truncatus). Both individual and synchronous breathing rates were the highest when animals engaged in energetic or social behaviors. Individual breathing rate decreased but synchronous breathing rate increased with the presence of enrichment. Both rates increased during unusual events (e.g., pool cleaning, presence of a diver in the pool, noise, transport) and when public was present for Yangtze finless porpoises. Finally, synchronous breathing rate increased for Yangtze finless porpoises when experiencing social separation. We suggest that individual and synchronous breathing rates are useful parameters to measure, both in wild and captive animals, to obtain information on their arousal/stress state. However, these rates should be interpreted with caution and should be used together with other parameters to allow more accurate inferences.