Spatial and temporal domains of scale of grazing cattle

Abstract

Spatio-temporal patterns of cattle grazing were studied in four annual grassland pastures in California, differing mainly in tree canopy cover. Cows were equipped with global positioning collars that recorded position, temperature and head movements at 5-min intervals during 6 days in each of four seasons repeated during 2 years. The time animals took to traverse areas of varying diameter revealed patches of 6–9-m diameter in the pastures with low, and 18–21-m diameter in the pastures with high tree canopy cover. In agreement with the current model, crookedness of cow paths had two distinct domains. Within distances of 0–40 m, paths were relatively straight and similar, but from 40 to 200 m, they became increasingly tortuous. Correlation of sequential turning angles identified patches of movement with diameters between 40 and 100 m, which correspond to the ‘patch’ level of grazing within grazing sites. Seasonal changes in meal patterns were consistent with changes in temperature and forage quality and interacted with the distribution of shade. Thus, spatial distribution of grazing and temporal distribution of meals were inextricably linked. Low forage quality and high temperatures in summer resulted in highly concentrated grazing around trees. Conversely, winter and early spring forages of very high quality and low availability motivated more widely distributed grazing, with low proportion of areas being re-grazed. Resting sites acted as beginning and end of grazing bouts. We conclude that shade distribution can modulate meal start and duration.