1. Sixteen Common Tern colonies in Rhode Island, New Jersey, Virginia, and North Carolina were studied from May through July 1980 by four investigators. Nests were marked during egg laying and were monitored every 5-7 days until fledging of young. 2. Results from 1980 indicate that ambient temperature differences in the four study areas account for differences in the onset of egg laying with North Carolina and Virginia colonies beginning 12-16 days before New Jersey and Rhode Island birds. Temperature alone, however, does not seem to have a significant effect on either median egg-laying dates or total duration of the season. 3. The low frequency of late-season nesting was not correlated with colony size or success of peak nests in 1980, but renesting (or late nesting) in all study areas was rare because of the benign weather conditions during the spring. Similarly, no significant correlation was found between success of nests and colony size.