The effects of habitat on the vigilance of shorebirds: Is visibility important?

Interference from adults forces young red knots to forage for longer and in dangerous places

“…We recorded the proportion of time spent vigilant with respect to predator encounter frequency, distance from cover and flock size. Head-up vigilance was defined as the raising of the head from a head-down foraging position to at least a horizontal position (Metcalfe, 1984).…”

Difficulties in Monitoring Conspecifics Mediate the Effects of Visual Obstruction on the Level and Synchronization of Vigilance

“…Many features of the habitat, however, can obstruct the field of view during vigilance. Examples include stubble in a field (Murton and Isaacson, 1962), rocks on the shore (Metcalfe, 1984), and vegetation cover (Underwood, 1982). Visual obstruction can thus interfere with vigilance and increase predation risk (Lima, 1987).…”

Factors Affecting Group Spread within Wild Mixed-Species Troops of Saddleback and Mustached Tamarins

“…This suggests that 7 individuals alter their vigilance in response to the ease with which they can perceive predators 8 within their surroundings. Similarly, Metcalfe (1984) showed that the visibility of other group 9 members influenced vigilance. If so, individuals that differ physiologically in their perceptual 10 capabilities may be expected to differ in their spatial ecology, since they will differ in their 11 perception of predators, conspecifics, and other objects within their environment.…”