Relation of environmental factors to breeding status of royal and sandwich terns in South Carolina, USA

The population ecology of the royal tern Sterna maxima and sandwich tern Sterna sandvicensis was investigated in South Carolina from 1970 through 1977. Royal and sandwich terns nested together in all of the colonies that we located.

The peak in egg laying usually occurred in early May; peak hatching occurred from late May to mid-June. Clutch size for both species was one egg. Tidal flooding was the major factor in egg loss.

The breeding population was 15,499 pairs in 1974 and 18,096 pairs in 1975; sandvicensis made up about 5% of the breeding population. The average number of young fledged per nest ranged from 0·36 to 0·44.

Residues of organochlorine pollutants in most eggs and tissues were low and posed no identifiable threat to the terns. There was a decline in DDE and dieldrin residues in eggs of maxima.

The future of royal and sandwich terns in South Carolina seems fairly secure as the population is apparently at or near carrying capacity and most of the major nesting sites are dedicated to protection of nesting birds.