Hexagonal Packing of Royal Tern Nests

Buckley, P.; Buckley, F.

Observed nest density as well as nearest-neighbor internest distances in a colony of Royal Terns on the southeastern U.S. coast demonstrate that the species has achieved an exceedingly close approach to maximal or hexagonal packing of its nests, probably the first firm demonstration of this effect in any aspect of a vertebrate social system. Various formulas for calculating both deviations from randomness and approaches toward hexagonality are discussed, using data in the form of nearest-neighbor distances, or in the form of nest density per unit area. The biological significance of Royal Terns' hexagonal nest packing is related to the species' high degree of sociality and low levels of aggression, and while observed predation on them at nesting time seems limited to egg-stealing (heaviest on the colony periphery), it is likely that the high nest density demonstrated here did evolve originally in response to just this sort of peripheral predation, synergistically magnified by the species' colony site choice of tiny shoals and sand bars with drastically reduced spaces for nesting.-North Atlantic Regional Office, National Park Service, 150 Causeway Street, Boston, Massachusetts 02114, and Manomet Bird Observatory, Manomet, Massachusetts 02345. Accepted 23 May 1975.

Hexagonal Packing of Royal Tern Nests

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