Characteristics of successful nest sites for marsh-nesting common terns

Abstract

The relationship between nest site characteristics and nest success during tidal flooding was studied in six New Jersey colonies of marsh-nesting common terns (Sterna hirundo). Most colonies were on high ground with a northeast water exposure, and almost all nests were on mats of dead vegetation. Terns nested on the thickest areas of the mats and, whether nesting on mats or on the ground, they selected nest sites with low vegetation density. The characteristics of successful nests differed with the height and date of the flood tide, and with wind direction. In the 1975 flood, nests on high ground were more successful, whereas nests in tall grass and on large mats successfully survived tidal flooding in 1976. Because grass height and ground height are negatively correlated in the marsh, it is difficult for the terns to maximize both characteristics when selecting a nest site. The large mats associated with flood survival in 1976 were also associated with higher prédation rates, indicating a further complication in selecting a safe nest site. Data from these floods were compared with floods studied by other researchers to further test whether certain nest site characteristics are associated with nest success in different types of floods.