WIND EFFECTS ON PREY AVAILABILITY - HOW NORTHWARD MIGRATING WADERS USE BRACKISH AND HYPERSALINE LAGOONS IN THE SIVASH, UKRAINE

Large numbers of waders migrating northward in spring use the Sivash, a large system of shallow, brackish and hypersaline lagoons in the Bla ck Sea and Azov Sea region (Ukraine). The bottoms of these lagoons are often uncovered by the wind. Hence, for waders the time and space ava ilable for feeding depend on wind conditions. In hypersaline lagoons t he benthic and pelagic fauna was very poor, consisting mainly of chiro nomid larvae (0.19 g AFDM.m-2) and brine shrimps Artemia salina, respe ctively. Brine shrimp abundance was correlated with salinity, wind for ce, wind direction and water depth. Dunlin Calidris alpina and curlew sandpiper Calidris ferruginea were the only species feeding on brine s hrimp. As brine shrimp densities are higher in deeper water, smaller w aders such as broad-billed sandpipers Limicola falcinellus are too sho rt-legged to reach exploitable densities of brine shrimp. In brackish lagoons the benthic and pelagic fauna was rich, consisting of polychae tes, bivalves, gastropods, chironomid larvae, isopods and amphipods (8 .9 to 30.5 g AFDM.m-2), but there were no brine shrimps. Prey biomass increased with the distance from the coast, being highest on the site that was most frequently inundated. Dunlin, broad-billed sandpiper and grey plover Pluvialis squatarola were the most abundant birds in the brackish lagoon. Due to the effects of wind-tides only a small area wa s usually available as a feeding site. Gammarus insensibilis was the a lternative prey resource in the water layer, and their density varied with wind direction in the same way as brine shrimp. Curlew sandpipers and dunlins in the hypersaline lagoons and broad-billed sandpipers in the brackish lagoons often changed feeding sites, probably following the variation in prey availability. Only because of the large size and variety of lagoons are waders in the Sivash always able to find good feeding sites.