Group size effects in jackdaw flocks

Bird flocks may range in size from only a few birds to hundreds or thousands. Characterizing the ways in which the structure and properties of flocks vary with the size is critical for understanding their dynamics and function. We will describe the structure and dynamics of more than 100 transit flocks of jackdaws, a highly social corvid species, measured in the field. We find that some properties, such as the bird number density, vary with size but saturate quickly. Other properties, such as the typical speeds, appear to be independent of flock size. We interpret our results in the context of the (topological) interaction range in flocks and compare them with similar measurements in insect swarms.