Impacts of free-ranging yaks on habitat occupancy and population density of a high-mountain rare pheasant species

Abstract

Free-ranging yak grazing is a regime specially adapted to high-elevation environments across the Pan-Tibetan Highlands, yet its impacts on alpine birds remain poorly understood. The Chinese Monal (Lophophorus lhuysii) is a rare pheasant species that serves as a representative and umbrella species for alpine meadow ecosystems in the mountains of Southwest China, and has long been regarded as threatened by free-ranging yaks. However, the actual impacts and specific mechanisms through which yak grazing influences Chinese Monal have not been empirically tested. Here, we conducted infrared camera monitoring in alpine meadows within the Wolong National Nature Reserve, Sichuan, China, from 2019 to 2022. We analyzed the effects of free-ranging yaks on habitat occupancy, activity pattern, and population density of the Chinese Monal using multispecies occupancy models, kernel density estimations, avoidance attraction ratios, and random encounter models. We found that interactions with yaks affect monal habitat occupancy in conjunction with other ecological factors. Specifically, the presence of yaks alters monals’ occupancy responses to variations in grass cover and elevation, causing monals to use habitats with lower grass cover and elevation more frequently. Additionally, the activity patterns of the Chinese Monal and yaks are significantly different, and the presence of yaks significantly prolongs the time until monals re-occupy the same habitats. As an outcome of the cumulative effects of spatial and temporal avoidance, the population density of the Chinese Monal negatively correlated with increasing grazing intensity. This study provides the first empirical evidence of the negative impacts of free-ranging yaks on the Chinese Monal and elucidates the underlying mechanisms, highlighting great risks to conservation of this vulnerable species. Our findings inform the optimization of grazing management that balances production with conservation. Strict control over yak numbers and grazing areas in critical habitats for Chinese Monal and other threatened species could be a feasible compromise to mitigate these pressures.