Factors that affect detection of threats from food competitors within a group.

Early detection is crucial to avoid threats from predators and competitors. Factors that affect threat detection have rarely been investigated in the context of food competition. I examined the ability to detect threats of displacement from feeding areas by competitors in flocks of staging Semipalmated Sandpipers (Calidris pusilla (L., 1766)). I predicted that targeted birds would be more likely to detect competitors attacking from the side or from the front rather than from behind because a blind area behind the head interferes with detection. Preening or sleeping birds in feeding areas might be less likely to detect attacks if such activities interfere with vigilance. If targeted birds maintain vigilance against attackers, attacks launched from farther away should be detected more frequently since more time is available for detection. As predicted, attacks were detected less often when launched from behind and more often when launched from farther away. The longest attacks were detected less often perhaps because birds relaxed their vigilance when neighbours were farther away. The ability to detect threats did not vary with targeted bird activity. Several factors influence the ability to detect threats from food competitors providing us with a novel context in which to investigate threat detection. [ABSTRACT FROM AUTHOR]