Behavioral patterns of yaks (Bos grunniens) grazing on alpine shrub meadows of the Qinghai-Tibetan Plateau

摘要

Proliferation of shrubs at the expense of native forage in pastures has been associated with large changes in biomass and spatial distribution of forage for grazing livestock, and such changes influence the grazing behavior of ruminants. However, little information is available concerning the effect of pastoral shrub coverage on grazing pattern. To better understand the grazing behavior of yaks and their response to increased shrub coverage in alpine meadows, 48 yak steers were randomly assigned to four pastures with shrub coverage of 0, 5.4 %, 11.3 %, and 20.1 % (referred to as control, low, middle, and high, respectively) on the Qinghai-Tibetan Plateau. The primary behavioral patterns (grazing, walking, and ruminating/resting) of three focus animals per experimental group were recorded repeatedly in scan sampling every 10 min from 07:00 to 19:00 h in three observation periods (the first 10 days of each month) from July through September. Furthermore, the secondary behavioral patterns (bites per minute, steps per minute, and bites per step) were observed 15 times per focus yak on each observation day. Behavioral observations showed that yaks had similar diurnal behavioral patterns with two main grazing bouts-in the morning and afternoon-and a ruminating/resting peak at midday when grazing in pastures with different shrub coverage. However, yaks significantly enhanced the time allocated to walking (P = 0.029) and decreased ruminating/resting time (P = 0.045) with increasing shrub coverage, although the grazing time was not significantly different (P = 0.663). Compared with the control and low shrub-coverage groups, yaks in the middle and high groups had more bites per minute (P = 0.036) and steps per minute (P = 0.029), whereas the number of bites per step was not influenced (P = 0.877) by shrub coverage. The increased time allocated to walking at the expense of ruminating/resting as well as the high number of feeding stations may be an adaptive strategy for searching and obtaining sufficient forage resources. Increased walking time and step rate for the yaks grazing in the high shrub-coverage pasture could increase the energy expenditure and consequently reduce the energy available for growth and production. Our findings provide evidence for the influence of shrub coverage on grazing behavior of yaks grazing in alpine meadows as well as insights into the sustainable production of grazing yaks on lands with increasing shrub coverage on the Qinghai-Tibet Plateau.