Fitness benefits of grouping during foraging in beef cattle: Social behaviour or affinity to vegetation resources?

Abstract

Grouping behaviour in gregarious species expresses a dynamic cost-benefit equilibrium. The balance between costs and benefits differs amongst individuals that were selected to maximize their individual fitness. In environments where resources are limited, benefits of grouping may come at the expense of increased competition over resources. This study aimed to test whether grouping behaviour during foraging in a free-ranging beef cattle herd is a social choice bearing fitness benefits for all participants, or reflects affinity to vegetation resources with possible differentiating fitness benefits. GPS location data were recorded in a herd of 60 beef cows grazing a semi-arid pasture in northern Israel. Pasture vegetation was chemically and spectrally analysed. GPS location data were used to investigate individual and shared foraging locations and the temporal sequence of initiating foraging movement. Co-travel function in ArcPro v3.0 was used to investigate the amount and variability of individual proximity associations and their correlation with fitness. Fitness proxies were conception result (yes/no) and the interval between calving and conception within the cows who conceived. A positive correlation was found between fitness and the individual number of proximity associations, but not with the variability in associations' partners. No significant correlations were found between fitness and vegetation biomass, N content and spectral properties measured by REEVI2 index in foraging locations. Individual sequence of arrival at shared foraging locations and foraging movement initiation sequence were also not correlated with fitness. Vegetation biomass in grouping locations was lower than in individually foraged locations, but no difference was found in N content between individual and shared foraging locations. No differences were found in vegetation biomass and N content between herd foraging locations and random locations, thus no evidence for herd foraging strategy aimed to increase biomass or N consumption was found. No further differences in pasture resources availability, i.e., water, shade, human or predator presence could explain grouping. Circular variance values implied the absence of preferred movement direction. Our results suggest that grouping during foraging is fitness beneficial and is not related to vegetation biomass or N content. Our results further suggest the absence of consistent leading individuals and no significant correlations between foraging movement initiation and fitness. This study provides insights into social and vegetation factors affecting cattle foraging behaviour in constrained pasture, and may allow ranchers to improve grazing management systems. We suggest that further research into pasture characteristics that affect beef cattle pasture location choice is needed.