NEST-SITE SELECTION OF THE BLACK TERN IN WESTERN NEW-YORK

Black Tern (Chlidonias niger) nest site selection and habitat availabi lity were investigated in 1994 and 1995 at the Iroquois National Wildl ife Refuge and adjoining Tonawanda and Oak Orchard State Wildlife Mana gement Areas in western New York. Nest site selection was evaluated wi th a logistic regression model using habitat variables collected in 26 12-m radius circular nest plots and 31 random non-nest plots. Signifi cant model variables were vegetation density, horizontal cover 0.5 m a bove the water, cover:water ratio, and water level. The model correctl y classified 77.2% of all plots. Most nests (84.6%) were in sparse to moderately dense vegetation. Horizontal cover 0.5 m above the water le vel was less than or equal to 50% in 84.6% of nest plots as compared t o 58.1% of random plots. Cover:water ratio was medium (40%-60% cover) in 65.4% of nest plots, while random plots were evenly distributed amo ng the low medium, and high cover:water ratio categories. Mean water l evel at nests was 48.2 cm and 42.1 cm in 1994 and 1995, respectively, similar to random plots. More than 80% of the nests were in bur-reed ( Sparganium spp.) in both years. Habitat availability was evaluated by classifying all emergent vegetation within the study area into 4 habit at quality categories. Highly Favorable Habitat (HFH) was habitat in w hich the model predicted greater than or equal to 0.50 probability of a nest site and suitable nest mats were available. Only 7.5% of the to tal available emergent vegetation in the study area was classified as Highly Favorable. Black Terns selected nest sites in HFH more than exp ected and used 72.5% of the total area of HFH in nesting marshes and 5 1.4% of the total area of HFH in all marshes within the study site in 1995. Muskrat (Ondatra zibethicus) structures were the most frequently used nesting substrate in both years. HFH could become limiting if th e size of this breeding colony increases or if nest site selection is influenced by social structure of the colony, habitat patch size and i solation, nesting density, or substrate availability.