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Zusammenfassung:
Diurnal and seasonal variation in foraging behaviour of Yellowhammers Emberiza citrinella and activity of their avian predators were studied in an unmanipulated winter field situation around Uppsala, Sweden. In December, when time available for foraging was lowest, Yellowhammers seemed to be time-stressed. In order to meet their energetic needs, they reduced the time allocated to vigilance and increased the time allocated to foraging. Yellowhammers did not systematically change the time spent foraging during the day in December, which indicates time-stress, while they decreased the time spent foraging during the day in both November and February. Predator activity was highest in the afternoon, when Yellowhammers spent the least time foraging. Yellowhammers may have adopted a routine with decreasing foraging rates over the day in November and February, when time available for foraging was longer, in order to avoid foraging during periods of high predator activity. The diurnal activity pattern of predators together with daylength and energetic needs are factors that might be important in shaping daily foraging routines in small birds.
