Abstract
In recent decades, the tight mutual specialization between nectarivorous birds and ornithophilous plants has been questioned, and instead, high degrees of generalization and interaction asymmetry have been highlighted. Here, we studied interactions among two sunbirds and four plant species in two Mount Cameroon forests, with two plant species from each forest.
First, we investigated whether sunbirds differ in frequencies of visitation to target plant species in natural conditions. Second, using a cage experiment, we investigated whether sunbirds prefer various plant species, plants with which they are more familiar and that occur in the habitat where they were caught and/or the only studied ornithophilous plant, Impatiens sakeriana.
In natural conditions, the short-billed sunbird, Cinnyris reichenowi, fed more on flowers with shorter tubes than the long-billed sunbird, Cyanomitra oritis. Likewise, sunbirds differed in their experimental preferences.
Local plants were generally preferred. This was most obvious in the case of I. sakeriana, which was often visited by both sunbirds, but only in the habitat where it grows naturally.
This study supports the importance of associative learning. Together with other studies, we suggest that the signalling traits of flowers with bird pollination syndromes evolved to filter out other visitors rather than to attract bird pollinators.