Cheleuitte-Nieves, Christopher (2011-08). Seasonal and Diurnal Patterns of Spatial Spread, Grouping Dynamics and Influence of Resources on a Free-Ranging Cattle Herd in a Semi-Arid Rangeland in South Texas, USA. Doctoral Dissertation.
Knowledge of scale-dependent factors that affect the distribution of ungulate herds, such as cattle, is essential for the development of more accurate predictive models of animal movement and the management of sustainable agriculture. Our objectives were to evaluate the seasonal and diurnal patterns of herd spread, explore grouping dynamics, and the influence of dominance ranks, seasonal changes in forage biomass, use of shade, water and supplemental feed areas on cattle distribution. Positional and activity information of eleven free-ranging Bonsmara, Bos taurus, cows were obtained at five minute intervals using Global Positioning System collars. We conducted a total of 12 trials each of three weeks from August 2007 to August 2009 in a 457ha shrub-dominated savanna in South Texas. Spread was obtained by calculating the average Euclidean distance of individuals to the center of the herd. The association software package, ASSOC1, was used to analyze spatio-temporal interactions. Normalized Difference Vegetation Index, an indicator of available forage biomass, was calculated using satellite imagery. Number of GPS fixes was used as an indicator of animal use of shade patches and water and supplemental feeding areas. In this semi-arid environment, herd spread was greatest and subgroup division occurred during summer when forage biomass was high. Herd spread was the least and shade patches were used more during winter when forage biomass was low. Throughout the year spread was smallest and use of shade patches highest during the midday period compared to other periods of the day. Location of individuals in the center of the herd was not associated with their dominance ranking. There was no significant overall pattern of seasonal changes in cattle use of water and supplemental feeding areas. Seasonal forage availability and shade patches seem to have a greater influence on herd dispersion patterns and grouping dynamics than any effect of social dominance. Herd distribution is likely related to changes in forage biomass and temperature fluctuations which drive compensatory night-time feeding and thermoregulatory actions. Accurate ethological studies of herds depend on our ability to understand herd dynamics at multiple scales that affect and are relevant to animal's response to the landscape.