Abstract:

Aims: The estrous behavior of polygynous ruminants is strictly seasonal, and males exhibit complex display behaviors during the rut, with vocal activity serving as an important display. The Milu (Elaphurus davidianus) is a typical large polygynous ruminant. During the rut, stags attract females and repel rivals through frequent roaring. This species has a large home range and a prolonged estrous period, making long term monitoring of its reproductive status challenging. Passive acoustic monitoring (PAM) technology has become an effective method for tracking vocalization behavior and population dynamics of wildlife due to its convenience, covertness, and capacity for long term operation. In this study, we employed PAM technology to conduct long term tracking of vocal activity in Milu across the rutting season. 

Methods: We employed PAM technology to record the group vocal activity of a Milu herd throughout the rut. Based on 92 days of acoustic data, we analyzed the seasonal and diurnal rhythms of vocal activity, examined the temporal coordination between mother - calf call interactions and the vocal activity of stags, and explored the effects of meteorological factors on the number of rutting roars produced by stags. 

Results: Vocal activity increased progressively as the rut advanced, peaking in mid July. The diurnal rhythm exhibited a distinct multimodal distribution, dominated by two primary peaks at dawn and dusk, with smaller peaks also occurring in the morning, afternoon, and at night. Calls of females and calves were highly synchronized, and mother - calf call interactions promoted vocal activity in rutting stags. The vocal intensity of rutting stags fluctuated with meteorological conditions and was significantly correlated with temperature, precipitation, and solar shortwave radiation, but not with wind speed, humidity, or atmospheric pressure. 

Conclusion: The vocal activity of Milu exhibited pronounced rhythmicity. Mother - calf call interactions promote the vocal activity of rutting stags, whose vocal intensity also fluctuates with meteorological conditions. This study provides valuable data for ecological monitoring of acoustic activity patterns in large ungulates during the rut and validates the feasibility of PAM technology for long term monitoring of large wildlife.

Key words: Elaphurus davidianus, rutting season, vocal activity, meteorological factors, passive acoustic monitoring