Feeding-Vigilance Trade-Off in the Teal (Anas Crecca): Effects of Feeding Method and Predation Risk

Abstract

AbstractFeeding and vigilance are conflicting demands in teals (Anas crecca) that use feeding methods where the eyes are beneath the water surface. This trade-off was compared across different beneath-surface feeding methods (head submerged, neck submerged, upending) and between the absence and presence of live predators, ospreys (Pandion haliaetus). A comparison across feeding methods indicated that the proportion of time spent scanning for predators and scanning rate decreased from head submerged to upending. Similarly, within a particular feeding method the level of vigilance decreased as average feeding bout length increased. Teals thus sacrificed vigilance as foraging demands increased. When a predator was present, however, teals increased the proportion of time spent scanning at the expense of feeding time in all feeding methods. This was achieved by lengthening scanning bouts, not by increasing scanning rate. As a consequence, feeding efficiency decreased. Feeding methods differed in terms of predator detection probability. An examination of the role of grouping in increasing predator detection probability indicated, however, that grouping would provide only a marginal benefit to foraging teals in this respect, whatever the feeding method.