Morphological adaptations for nectarivory in birds

Scientists have been interested in adaptation of nectar-feeding birds for a long time. I tried to summarize information about these adaptation. About hummingbirds's, sunbird's and honeyeater's bill and tongue, about body size and how flower influences nectar intake. Nectar-feeding birds has extended and curved bill, which is an adaptation to flowers visiting by these birds. The tongue is a tool for nectar intake, its inner structure allows nectar intake. Tongue is tubular and hummingbird's and sunbird's tongue is proximal bifurcate, honeyeater's tongue has brush tip. Nectar-feeding birds are generally of small body size and larger species have to intake more insects because of higher energetic requirements. Some flowers don't allow to perch and nectar-feeding birds have to intake nectar in flight. Therefore especially hummingbirds and some sunbirds evolved a hovering. If its possible, these birds perch when they collect nectar