Contribution to the breeding occurrence of the black tern, Chlidonias niger, in Schleswig-Holstein from 1966 to 1969

Abstract

1. Between 1966 and 1969, a total of 101 different breeding sites for the black tern were identified in Schleswig-Holstein. In addition, there are six questionable breeding sites.

2. Forty-nine breeding sites are located in the marshes, 31 in the geest, and 21 in the eastern hills. Seventy-five percent of the breeding sites are located within a 40 km radius of Friedrichstadt on the west coast. The highest colony density is found in Eiderstedt and Norderdithmarschen.

3. The total number of breeding pairs recently recorded in the individual breeding colonies is 570, suggesting a total breeding population of around 800 breeding pairs.

4. The breeding colonies are spread across three different breeding habitats: a. Drinking troughs, ditches (38 breeding sites), b. Moors (40). c. Lakes, ponds (23). The immediate nesting habitat, which serves as a base and support for the nests, is subdivided in more detail and its decisive influence on the start of the breeding season is highlighted. The breeding pair strength of the individual colonies can be seen in Table 1: Breeding colonies with 5-15 breeding pairs are most common.

5. The annual population fluctuations of the individual colonies are shown in Tables 1 and 4. The following factors were identified as influencing the population: changes in water levels, storm losses, changes in the breeding habitat caused by humans, displacement by other bird species.

6. The population development of some key breeding areas indicates a strong downward trend. Over the last 25 years, the total breeding population in Schleswig-Holstein appears to have declined by more than 50%.