IMPORTANCE OF DOMINANCE STATUS AND DISTANCE FROM COVER TO FORAGING WHITE-CROWNED SPARROWS - AN EXPERIMENTAL-ANALYSIS

We address the importance of a nearby source of cover to foraging Whit e-crowned Sparrows (Zonotrichia leucophrys) belonging to different cla sses of social status and plumage. An artificial source of cover was p rovided, in the form of a constructed bush, which allowed manipulation of the degree and position of cover. In various manipulations, the bi rds were offered no cover, the position of the cover was switched, and a simple perch was offered as an alternative to the bush. White-crown ed Sparrows usually perched first in a nearby source of cover before t hey fed, and strongly preferred to feed dose to the artificial bush. E xperiments demonstrated that the bush was used as a source of cover an d not merely as a perch. The bright-colored dominant adult birds fed c loser to cover than did the more subordinate, dull-colored, and relati vely cryptic immatures. Adults apparently displaced the latter from si tes close to cover as immatures fed closer when no adults were present . These results may explain why dull-colored subordinate birds do not cheat by displaying the brighter plumage of dominant sex/age classes. Cheaters might be more prone to predation than noncheating subordinate s because both classes might be forced to feed away from cover by inhe rently dominant birds (i.e. actual adults), but cheaters would be more conspicuous than noncheaters due to their brighter plumage. Thus, the potential benefits of cheating may not outweigh the increased cost of heightened susceptibility to selection by a predator.