Priorities for Future Research

The largest gap in knowledge of the Common Tern in the Western Hemisphere is its ecology in winter quarters. Although the winter distribution on the east coast of South America is reasonably well known, little is known about the species there except its occurrence at nocturnal roosts on the shore. On the Pacific Coast, even the distribution is poorly known. Because most mortality is believed to occur in winter, the population dynamics of the species will not be understood until more is learned about its foraging ecology, energetics, molt, causes of death, and other limiting factors operating in the winter quarters. In breeding areas, more information is needed on the basic natural history and ecology of the small isolated populations on the northern Gulf Coast, in Bermuda, and in the southern Caribbean, as well as their genetic relationships to the much larger continental populations. The Gulf Coast population is probably critically endangered and urgently needs study and conservation. Wider studies of the entire genus Sterna using modern molecular genetic techniques could clarify the relationships between Common Terns and several similar species of the Northern and Southern Hemispheres. More banding is needed in Québec and Manitoba to identify the locations and sharpness of the migratory divides between regional populations. More direct comparisons between the ecology and physiology of the populations breeding on salt and fresh waters would be valuable, including studies of the transition of fresh water birds to marine foraging in winter. Most of the published studies of displays and communicative behavior were conducted more than 40 years ago; they should be repeated using up-to-date techniques and concepts. The vocalizations of this species have never been studied systematically. Although natal dispersal and breeding dispersal have been documented in the Great Lakes, there is little precise information about dispersal among coastal colonies, despite many decades of chick banding and adult trapping; there are good opportunities for cooperative analyses or newly-designed studies to elucidate metapopulation dynamics. Finally, detailed studies of factors affecting the breeding performance of individual birds should continue. The extensive existing knowledge of the species can provide a sound basis for further detailed studies of basic questions in evolutionary and behavioral ecology.