Short-term learning and the searching accuracy of egg-laying butterflies

Searching constraints influence foraging patterns in three species of Colias butterflies. The activity of egg-laying females is partitioned into periods of searching for oviposition plants and periods of visiting flowers for nectar. Eggs are laid most frequently upon legume host-plants, although females frequently land upon non-legume species, particularly those bearing a superficial resemblance to suitable hosts. The average frequency of these landing ‘errors’ decreases over the course of an egglaying flight, implying thet females learn to identify host-plants more accurately on the basis of recent experience. Landing accuracy is low after periods of nectar-feeding, which suggests a trade-off between the two searching modalities. Within oviposition sequences, females that visit a narrow range of host specis make fewer landing errors than females visiting a broader host-plant set. Two interpretations of these data are presented: (1) that partitioning searching time into discrete modes may enhance overaccuracy in invertebrates, as has been demonstrated previously for vertebrates. Searching dynamics of this type may explain some discrepancies between the predictions made by simple optimal diet models and the occurrence of ‘switching’ behaviours in foragers.