Spatial Relationships in Flocks of Sandhill Cranes (Grus Canadensis)

The Clark—Evans model of spatial distribution was applied to aerial photographs of flocks of Sandhill Cranes feeding in cultivated fields. Distance to nearest neighbor for a total of 1,326 individuals in 29 flocks varying in size from 3 to 252 birds had a mean value of 5.79 ± 0.16 ft and was remarkably uniform, regardless of flock size. Departure from random spacing was consistently in the direction of uniform spacing, although the degree of uniformity varied inversely with flock size. A modified model based on flocks occupying circular areas and composed of sub—groups, with a constant individual distance within groups and an additional space factor between groups, seems to provide a reasonable interpretation of dispersion in different—sized flocks of Sandhill Cranes. A conclusion drawn from the correspondence between the theoretical model and the data and observations is that large flocks of Sandhill Cranes are loosely organized assemblages of smaller groups which behave more as coordinated units and are based on a relationship of individual distances.