Seasonal movement behavior of domestic goats in response to environmental variability and time of day using Hidden Markov Models.

Abstract

Background: Current research on livestock movement ecology focuses on quantifying the factors that trigger alterations in movement behavior and understanding hidden mechanisms. Modern tracking technologies and robust statistical analysis models deliver new opportunities for investigating how individual animals cope with the joint effect of biotic and abiotic factors at different time scales.

Methods: We applied multivariate Hidden Markov Models (HMMs) to characterize the fine-scale movement behavior (30-second intervals) of GPS-tracked domestic Zhongwei goats (Capra aegagrus hircus) for 124 days and analyzed the combined influence of biotic and abiotic factors and specific time of day on their seasonal movement behavioral transition in a predator-free, semi-arid mountain grassland in China.

Results: We classified the behaviors of goats into two states: foraging (low step length, varied turning angle) and travelling (long step lengths, small turning angles). The terrain slopes had the most impact on their movement behavioral transition in the full year, spring, autumn, and winter. However, in the summer with hotter temperatures, the specific time of day explains their movement behavior most. Forage resources indicated by the Normalized Difference Vegetation Index (NDVI), and terrain ruggedness measured by the Vector Ruggedness Measure (VRM), had less impact on their behavior transitions compared to terrain slope and specific time of day. Elevation and solar radiation could not explain their movement behavior in different seasons, nor could NDVI in winter or VRM in spring and autumn. Across different seasons, the probability of foraging behavior increased with the later times of day, steeper terrain slopes, and higher NDVI, while it decreased with increasing VRM. The impact of NDVI on the probability of foraging behavior was largest during the early onset of vegetation growth in spring, and lowest in winter coinciding with a lower availability of food resources. The movement speed was lower, and the daily foraging percentage was higher in spring and winter due to lower food resources and shorter daylight hours. In contrast, movement speed was higher, and the daily foraging percentage was lower in summer and autumn with more food resources and longer daylight hours. The percentage of time allocated to foraging increases hourly from 9:00 am to 8:00 pm across various seasons.

Conclusions: HMMs were found to be useful for disentangling the movement behavior of goats. Our approach provides new insights into the seasonal and daily behavioral strategies of goats. Results demonstrate that in the mountain region, terrain slopes and specific times of the day more effectively trigger domestic goat behavioral transition from one state to the next compared with biotic factors, represented herein by NDVI, across different seasons. The early onset of vegetation growth and a shorter period of available high-quality forage in spring, significantly influenced goat behavioral transitions. Overall, these results are important for designing appropriate grazing management strategies that satisfy the ecological and socioeconomic demands of semi-arid grassland ecosystems.