MOBILITY OF IMPATIENS-CAPENSIS FLOWERS - EFFECT ON POLLEN DEPOSITION AND HUMMINGBIRD FORAGING

Flexible pedicels are characteristic of bird-pollinated plants, yet ha ve received little attention in studies of hummingbird-flower interact ions. A major implication of flexible pedicels is that flowers may mov e during pollination. We examined whether such motion affected interac tions between ruby-throated hummingbirds (Archilochus colubris) and je welweed (Impatiens capensis) by increasing pollen deposition and by al tering the effectiveness of nectar removal. For I. capensis, flower mo bility enhanced pollen deposition: birds had significantly longer cont act with anthers and more pollen deposited on their bills and crowns w hen foraging at mobile flowers than at flowers that had been experimen tally immobilized. In contrast, flower mobility imposed a cost on humm ingbirds by significantly increasing their handling times and reducing their extraction rates relative to their interactions with immobile f lowers. Field observations indicated that the motion observed during h ummingbird visits did not occur when bees (Bombus spp., Apis mellifera ) visited I. capensis flowers, which suggests that the mobility of I. capensis flowers is an adaptation for hummingbird pollination.