The Influence of Spring Flood Water Levels on the Distribution and Numbers of Terns (On the Example of the Lower Desna River)

Abstract

The floodplain reservoirs of the lower Desna River are known to represent suitable breeding habitats for the Black Tern (Chlidonias niger) and the White-winged Tern (Chlidonias leucoptera), while the Common Tern (Sterna hirundo) and the Little Tern (Sterna albifrons) nest on sandy islands and river spits at the river bed. We combined analysis of Landsat 8 satellite images and the breeding abundance of the lower Desna River resident terns to investigate if the levels of the floodplain inundation affect the terns’ distribution and numbers. Under the high flood conditions of 2013, we observed a significant decrease in the numbers of colonies and nesting pairs of the Common and Little Terns, which was probably caused by the delayed exposure of their breeding habitats at the river bed. In contrast, in the low water conditions of 2014, areas of sandy islands and river spits increase in the form of temporary sandbanks. Under low-water conditions, we observed a marked increase of the number of colonies and nesting pairs of the Little Tern, while the White-winged Tern disappeared from nesting sites and the Black Tern decreased in numbers.