Predator detection and avoidance by starlings under differing scenarios of predation risk

Abstract

Practically all animals must find food while avoiding predators. An individual's perception of predation risk may depend on many factors, such as distance to refuge and group size, but it is unclear whether individuals respond to different factors in a similar manner. We tested whether flocks of foraging starlings responded in the same way to an increased perception of predation risk by assessing three factors: (1) neighbor distances, (2) habitat obstruction, and (3) recent exposure to a predator. We found that in all three scenarios of increased risk, starlings reduced their interscan intervals (food-searching bouts), which increased the frequency of their vigilance periods. We then examined how one of these factors, habitat obstruction, affected escape speed by simulating an attack with a model predator. Starlings were slower to respond in visually obstructed habitats (long grass swards) and slower when they had their head down in obstructed habitats than when they had their head down in open habitats. In addition, reaction times were quicker when starlings could employ their peripheral fields of vision. Our results demonstrate that different sources of increased risk can generate similar behavioral responses within a species. The degree of visibility in the physical and social environment affects both the actual and perceived risk of predation.

Habitat characteristics and seed crops used by Blue ChaffinchesFringilla teydeain winter: implications for conservation management

“…Buckingham & Peach 2006, Siriwardena et al 2007. Recent experimental research has also shown that seed-eating birds alter their foraging behaviour in response to vegetation manipulation (Devereux et al 2006, Whittingham et al 2006a) and the perceived predation risk has been suggested as a key factor explaining why granivorous birds prefer areas with greater visibility for foraging and feeding on the ground. Our results do not depart from this pattern because the occurrence of Blue Chaffinches in less sheltered locations (TC < 38%) was influence by the availability of pine seeds on the ground.…”

Predation of migratory Little Stint (Calidris minuta) by Barbary Falcon (Falco pelegrinoides) is dependent on body mass and duration of stopover time

“…Further, an important factor influencing the speed of predator detection is habitat structure (Whittingham et al 2004;Devereux et al 2006). In our case, the advantage is clearly with the falcons--open salinas, no escape routes or shelter, and foraging singly are all disadvantageous to the waders.…”

Modeling scan and interscan durations in antipredator vigilance

“…A greater visual acuity would result in the detection of threats at a greater distance. The presence of visual obstacles in the local environment, like vegetation cover or rocks, can also reduce the ability to detect a threat at a given distance (Arenz and Leger, 1997;Devereux et al, 2006;Lima and Zollner, 1996).…”

“…Predator presence is a well-known factor leading to longer scans in birds and mammals (Dacier et al, 2005;Devereux et al, 2006;Glück, 1987;Li et al, 2009;Mathot et al, 2009) although there are exceptions (Jones et al, 2007;Lima, 1992). Scan duration is also known to increase when animals are disturbed by people (Dyck and Baydack, 2004).…”

“…Alpine marmots (Marmota marmota) increased scan frequency but not scan duration in more visually-obstructed habitats (Ferrari et al, 2009). European starlings foraging in more visually-cluttered habitats reduced scan duration and interscan duration to increase scan rate (Devereux et al, 2006). Starlings increased their scanning when barriers blocked their lateral view but this scanning was mostly aimed at conspecifics rather than predators (Fernández-Juricic et al, 2005).…”