Numerous other birds can be seen, especially during the spring and autumn migration. Sand martins ("Riparia riparia") arrive early and can usually be seen hawking over the water for insects in the second or third week of March. Flocks of tits (Paridae), swallows (Hirundinidae) and terns (Sternidae) can regularly be seen. Waders, such as lapwings ("Vanellus vanellus"), dunlin ("Calidris alpina") and common snipe ("Gallinago gallinago"), are attracted to the muddy shores if the water level drops in autumn. By midwinter up to 55,000 gulls, mostly black-headed gull ("Chroicocephalus ridibundus") and common gull ("Larus canus"), may be roosting. Good numbers of reed warblers ("Acrocephalus scirpaceus") and sedge warblers ("A. schoenobaenus") nest in the fringing reeds, along with grebes (Podicipedidae) and Eurasian coots ("Fulica atra").