Movements and Conflicts in a Flock of Foraging Black-Tailed Godwits (Limosa limosa): The Influence of Feeding Rates on Behavioural Decisions

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.

Benefits of foraging in small groups: An experimental study on public information use in red knots Calidris canutus

Social foraging is common and may provide benefits of safety and public information. Public information permits faster and more accurate estimates of patch resource densities, thus allowing more effective foraging. In this paper we report on two experiments with red knots Calidris canutus, socially foraging shorebirds that eat bivalves on intertidal mudflats. The first experiment was designed to show that red knots are capable of using public information, and whether dominance status or sex affected its use. We showed that knots can detect the foraging success of conspecifics and choose a patch accordingly. Neither dominance status nor sex influenced public information use. In the second experiment, by manipulating group size, we investigated whether public information use affected food-patch discovery rates and patch residence times. We showed that the time needed before locating a food patch decreased in proportion to group size. Also, an individual's number of patch visits before locating the food declined with group size, and, to our surprise, their average patch residence time did as well. Moreover, knots differed in their search strategy in that some birds consistently exploited the searching efforts of others. We conclude that socially foraging knots have the potential to greatly increase their food-finding rate by using public information. This article is part of a Special Issue entitled: In Honor of Jerry Hogan.