Underwater foraging increases the incidence of head-up position in dunlin (Calidris alpina)

Antipredator vigilance may be affected by feeding techniques that obstruct animal’s vision, such as underwater foraging. I examined the effect of underwater foraging on head-up position in spring staging dunlins (Calidris alpina), predicting that this type of foraging would positively affect the frequency of head-up vigilance in this species. The results of analysis showed that significant predictors of the occurrence of head-up positions were underwater foraging and head-up position that occurred in the imminent past. Results of this study imply that dunlins are less likely to raise their heads above the shoulder line if they have not obstructed their vision by underwater foraging in the previous moment and that birds are able to acquire visual information from their surroundings not only when their heads are in the upright position but also during head-down foraging and/or during horizontal head position.