Abstract

Recent models have considered the problem of how a solitary animal should make efficient foraging decisions when it must acquire information while it forages. However, the presence of others likely has important consequences for this information-gathering (sampling) process. This thesis tests the hypothesis that when foraging socially, European starlings (Sturnus vulgaris) use both "personal information" (gathered from their own foraging activities) and "public information" (obtained from observing the foraging activities of neighbouring conspecifics) to direct their foraging decisions in a profitable manner. In an aviary experiment, the ability of captive starlings to use environmental cues discovered via their own patch exploitations and via those of others was examined to evaluate the contribution of each source of information to individual feeding efficiency in groups. The ability to recognize "public" cues correctly enabled starlings to take advantage of the foraging activities of others both by arriving at their profitable discoveries more quickly and by actively avoiding their unprofitable discoveries, thus saving valuable foraging time. In a series of aviary experiments, starlings were found to assess poor patches more rapidly by combining information obtained from their own unsuccessful sampling efforts with information obtained from observing the unsuccessful sampling efforts of another individual foraging in the same patch. The degree to which public information was used, however, depended on the cost of patch assessment; when this cost was high, personal sampling declined and the use of public information increased. Finally, in a field experiment, the ease with which personal and public information could be acquired simultaneously and the variability in patch quality were manipulated in order to determine what sources of information free-living starlings were using to monitor patch depletion. When both personal and public information were available simultaneously, starlings were sensitive both to their own foraging rates and to those of other flock members, and used this information to estimate patch quality and direct their patch departure decisions.