Common Terns prefer to nest on islands or in salt marshes in areas with sand, gravel, shell or rocky substrates with some scattered vegetation or other cover for sheltering chicks.  Colonies are generally placed within 20 km of foraging areas that have fish available 50 cm below the water’s surface (shallow coastal waters, bays, inlets, shoals, tide-rips, drift lines, saltmarsh creeks, lakes, ponds or rivers).  Common Tern nests are located 0-5 m above the high water mark and can be prone to washout from high tides. The species exhibits very high breeding site fidelity, although they will abandon a colony site and move en masse to another location because of predation or other causes of breeding failure.  Common Terns may be susceptible to crowding by other spceices; on the Atlantic Coast and the Great Lakes, colony sites have been occupied by Herring, Ring-billed, and Great Black-backed Gulls, forcing the birds into poorer quality habitat.  

For more information on Common Terns, including identification information, visit their page on the Cornell Lab of Ornithology.

Text References

1. Nisbet, I. C. T. 2002. Common Tern (Sterna hirundo).in A. Poole, editor. The Birds of North America Online. Cornell Lab of Ornithology, Ithaca 
2. Nisbet, I. C. T., J. M. Winchell, and A. E. Heise. 1984. Influence of age on the breeding biology of Common Terns. Colon. Waterbirds 7:117-126.