Effects of foraging mode and group pattern on vigilance behavior in water birds: a case study of mallard and black-winged stilt

Vigilance behavior is affected by many factors including foraging mode and group pattern which we attempted to understand through a case study of mallard Anas platyrhynchos and black-winged stilt Himantopus himantopus in the Hengshui Lake National Nature Reserve, China. Mallard, a swimming bird, forages in irregular and loose circular groups in open water and its foraging mode (with its head underwater looking for food) does not allow for simultaneous monitoring of potential threats above the water surface, which is why its foraging is called “blind period of foraging”. In contrast, black-winged stilt is a wading bird and forages along riversides in long linear foraging groups. Its long beak, neck and legs enable it to scan around while foraging without any obviously blind period. We used the focal sampling method and measured vigilance behavior by the time spent vigilant, vigilance frequency, average duration of vigilance, alert distance and flee distance for the two species. We predicted higher levels of vigilance and longer alert and flee distance in mallard with long blind periods of foraging. Our results indicated significant differences (p