DO WILD BIRDS USE SIZE TO DISTINGUISH PALATABLE AND UNPALATABLE PREY TYPES

A field experiment offering wild passerine birds three different sizes of pastry bait was performed to investigate whether the birds could use the size of the baits as a label for palatability. The predator population avoided medium-sized baits when they were made unpalatable with quinine and mustard powder if the size difference between the baits was large enough. The limits of this size-distinguishing ability varied with experience. Birds that learned a large size difference were better able to distinguish a smaller difference. The birds appeared both to learn with experience of the task, and to resample each day rather than generalizing from one day to the next. They did not appear to be able to detect quinine by sight or smell. The consequences of the ability to use size as a label of palatability are discussed in the context of a model-mimic relationship and the frequently smaller size of Batesian mimics. © 1993 Academic Press, Inc.