Bird migration over the open sea (BIRDMOVE)
Institute of Avian Research - Ornithological Station Helgoland
The German Bight is regularly crossed by land birds during migration between breeding and wintering sites. The rangeof species crossing the open water ranges from the smallest songbirds to large waterfowl such as geese and cranes. While general migration trajectories and timing are well described for many species, surprisingly little is known about movements of individual birds. Why, for example, does a blackcap choose to cross the open sea, while a conspecific prefers to follow the coastline? Especially in small songbirds, which are too light to carry GPS tags and fly rather secretly during the night, information on such individual decisions is scarce.
The BIRDMOVE project uses a network of automatic receivers located in the area of the German Bight (www.motus.org). Birds are equipped with small and light weighted, (approx. 0,25 gram) radio telemetry tags via leg loop harnesses. . These tags, can be located bythe receiver network. The two research platforms FINO1 and FINO3 in the North Sea are an important addition to the coastal network of receivers. For the first time, individual movement patterns of small songbirds with high spatial and temporal resolution are available at the German Bight.
Various songbird species are equipped with miniaturized radiotags. They send at very low power (in comparison: a cell phone emits 500 times stronger signals). Still, these individually coded signals, emitted every few seconds, are strong enough to be detected over a few kilometres by the receivers.
The birds selected for the study are medium and long-distance migrants. Medium distance migrants are e.g. blackbird, robin and song thrush. They cross the German Bight and spend the winter in Europe. The long distance migrants, e.g. Pied Flycatcher, Redstart and Whitethroat, cross the Sahara Desert to reach their wintering grounds.
This project aims at drawing a better picture of the reasons for individual routing decisions of song birds at the German Bight. Inner state, such as physical condition, as well as external conditions, i.e. the weather, will be analysed. Given the recent development of offshore wind farms already operating and still to be built in the German Exclusive Economic Zone, this study contributes to a better understanding of the potential risk of these new structures for nocturnal migrants. Consequently, it helps to further improve nature conservation assessment of offshore wind farms.