More complex anti-predator behaviors develop with age in Chinese water deer fawns

An anti-predator strategy increases the fitness of the prey itself, in which vigilance behavior plays an important role. Numerous studies have explored the correlation between prey age and the level of vigilance towards an approaching predator. However, limited studies have delved into the development of vigilant behaviors, much less the vigilant decision-chains. Chinese water deer (Hydropotes inermis), an extremely timid and sensitive animal capable of independent movement at birth, exhibits changes in vigilance strategy from newborn to the end of suckling period. Through individual recognition and standardized flight initiation trial, we measured the distances between the approaching predator and the occurrence of various vigilance behaviors (stare, flight, roaring, stretching neck, vigilant stomping). Our results reveal that Chinese water deer exhibited the vigilant strategy of roaring in the early stage (<3 weeks), and stretching neck and vigilant stomping in the late stage (≥10 weeks), displaying an overall trend of increasing complexity. The vigilant decision-chains of the fawns become more diverse with age. Fawns prioritize their own intrinsic status when making flight decisions under the same threat, with age, birth weight, and pre-flight behaviors emerging as the dominant determinants. Overall, our findings indicate that suckling fawns of Chinese water deer adopt different vigilance behavioral strategies with their development and depending on their age, birth weight and pre-flight behaviors when faced with a threat.