Final answer:
Goldfinches flocking to feed together on seed heads of plants demonstrate social behavior, which constitutes a social group due to their interaction and coordinated activities.
Step-by-step explanation:
Out of the given options, goldfinches flocking to feed together on seed heads of plants growing in open fields comes closest to constituting a true social group. A true social group involves the interaction among individuals, often to share resources or benefits, and mutual communication for coordinated activities.
Observing the patterns of population distribution and understanding the environmental factors influencing such patterns are essential in determining what constitutes a social group. Animals that travel in clumped distribution patterns, like goldfinches feeding together, exhibit social behavior. They may coordinate their actions for foraging or predator avoidance, suggesting a level of social organization unlike the passive aggregation of oak seedlings or the independent attraction of flies and cattle to food or water sources.