Species composition of foraging birds in association with benthic fauna in four intertidal habitats of the Wadden Sea

Abstract About 10 to 12 million birds per year use the intertidal flats of the Wadden Sea in north-eastern Europe as a food source during their moulting, wintering or breeding season and as a stop-over site along the East Atlantic Flyway. The tidal flats are inhabited by a highly productive benthic fauna representing an important link between the marine microflora and -fauna and higher trophic levels such as birds. Due to differences in the food preference, bird species might distribute on different habitat types formed in the Wadden Sea. In the present study, the diversity of foraging birds was studied in four intertidal habitats (seagrass meadow, sand flat, mud flat, Elbe tidal flat) and their macrozoobenthic food sources were analysed. Samples of benthic macrofauna were taken seasonally while foraging birds were counted monthly at the studied sites. Results revealed different benthic communities in each of the studied sites with large variation in abundance and diversity of foraging birds. Peak numbers of birds during spring and autumn reflected migration through the region. While the majority of bird species shows an opportunistic habitat choice, some species (e.g. Bucephala clangula, Philomachus pugnax) were observed foraging at one site only. However, results revealed only a weak link between bird assemblages and benthic communities within the tidal flats. As indicated by clear relationships between bird species abundance and tidal stage, avian distribution patterns are probably also strongly dependent on abiotic factors such as distance to roosting sites, inundation time and anthropogenic influences. Therefore, it is not sufficient to study the distribution of favoured prey items in the tidal flats alone but additional information needs to be taken into account to understand the complex distribution patterns of birds in the intertidal environment.