Foraging Patch Dynamics in the Teal (Anas Crecca): Effects of Sociality and Search Method Switching

The effects of social foraging and feeding method switching on foraging patch arrival-departure dynamics in the teal (Anas crecca) were studied. Overall patch arrival-departure dynamics was studied in three morning periods between 0300 h and 0900 h - early, mid and late morning. The arrival rate of flying individuals did not differ between morning periods but the departure rate increased from early to mid morning. The arrival rate of flying individuals exceeded the departure rate in all morning periods. In the course of a morning, teals switched their foraging methods so that feeding depth at the patch gradually increased. This indicated a decrease in patch quality and feeding rate. An important favourable consequence of search method switching was, however, that teals could lengthen their patch residence time. As patch quality further deteriorated (i.e. feeding depth increased more and more), teals responded numerically, and so that forager group size in the patch decreased. The increase in feeding depth may provide a cue when to leave a patch. Forager group size in turn affected the magnitude of the deterioration in patch quality; the greater the group size, the more rapid the deterioration.