What determines the time-activity budgets of Avocets (Recurvirostra avosetta)?

Time-activity budgets of birds are known to be affected by many different f actors. The aim of this study is to explain the intra-specific variation of activity patterns (in particular foraging activity) of one particular wade r, the Avocet. Sixty-seven series of scan observations of 12 h to 12.5 h le ngth were made at several sites on the flyway of the northwest European pop ulation and at various stages in the species' annual cycle. In estuarine ha bitats the activity pattern war mainly influenced by the tide. As soon as t he conditions allowed (neap tides) Avocets abandoned the tidal rhythm. No t ime of day effects on activity patterns could be detected. Activity pattern s by day and at night were essentially the same, except during very dark ni ghts (owing to artificial illumination at some of the study sites such nigh ts were a rare event), when foraging activity was reduced. The breeding sea son induced considerable changes of the activity patterns, including a redu ction of foraging time to less than 20% of the budget at the end of the bre eding season. Outside the breeding season, activity patterns were mainly in fluenced by the type of food (fish: reduced foraging time, Chironomid larva e: prolonged foraging time), by temperature (increase of foraging time with decreasing temperature), by windspeed (reduction of foraging time at wind speeds above 10 m/s) and by the darkness of the previous night (compensator y feeding after dark nights).