The Black Tern (Chlidonias niger Linn.): Breeding Ecology in Upstate New York and Results of Pesticide Residue Analyses

Abstract

The purpose of this study was to determine if there were factors in the breeding area that may be adversely affecting the Black Tern, with the major objectives being: 1) to determine the breeding success of a particular colony over a period of two summers; 2) to make observations on predation and competition; and 3) to collect any dead or disabled terns and abandoned or non-viable eggs for pesticide or other chemical contamination. This study was conducted over two consecutive summers, 1983 and 1984. During the summer of 1983, Yanty Creek Marsh was visited a total of 28 times from 19 May until 6 August, from one to five times per week. From two to seven hours were spent at the marsh at each visit with an average of about four hours per visit. The hours ranged from early morning to after sunset on different occasions. In the summer of 1984, a total of 40 visits were made to the marsh, consisting of approximately the same number of hours per visit as the previous summer. Early in the study, visits to the marsh consisted of walking along the Yanty Creek nature trail to determine when the terns first arrived. Later, a canoe was used to observe birds in the interior of the marsh. Due to the thick growth of cattails surrounding most of the nests, bringing a canoe directly within observational distance of the nest would have been too destructive of the cattails which may act as a protective surrounding of the nest site. Nests were located by walking through the marsh and noting the behavior of the adult Terns. Initially, the Terns were watched from a non-threatening distance to try and pinpoint the spot where they landed. Then, by moving closer to a nest by foot or canoe, one or more adults would give threatening calls which would increase in intensity as the nest was neared. The adult would fly around low over the cattails and momentarily hover over the nest before resuming the attack. This hovering act was the important key in locating the nests. Each time a nest was visited, the number of eggs and the number of dead or alive chicks was recorded. In the beginning of the season, the nests were marked with a numbered flag. However, as the summer progressed, it became more difficult to locate these flags due to the growing vegetation. Towards the middle of June, sticks measuring 1-2 meters tall were stuck into the mud near the nests, yet these also were barely visible some weeks later when scanning the tops of the cattails with a binocular. Thus maps and behavior of adults were used to locate the nests during the course of the summer.