YANEGA, GREGOR; RUBEGA, MARGARET; University of Connecticut: Placing intramandibular kinesis in hummingbirds in the context of tetrapod feeding evolution

During previous studies with ruby-throated hummingbirds (Archilochus colubris), we discovered a novel mode of intramandibular flexion in birds attempting to catch fruit flies. We document this mode of kinesis in two additional hummingbird species, magnificent hummingbird (Eugenes fulgens) and blue-throated hummingbird (Lampornis clemenciae). These findings suggest it is a widespread trait within the family Trochilidae (Apodiformes), and underscore the potential importance of this feature in the context of insectivory in hummingbirds. A survey of the literature reveals that members of other closely-related families, the swifts (Apodidae: Apodiformes) and nighthawks (Caprimulgidae: Caprimulgiformes), also use some form of mandibular kinesis for the purpose of aerial insectivory. The kinesis of hummingbirds differs from these other two groups in certain key respects (both morphological and ecological), and these three differ from all other birds capable of mandibular kinesis (1) in the elements of the bones responsible for the motion of the mandible, (2) in the extent of mobility and direction of the motion in the lower jaw, and (3) in their use of both cranial kinesis (mobility of the upper jaw relative to the brain case) as well as mandibular kinesis. As such they represent a potentially informative reversal in an avian trend toward fusion of elements of the jaws and skull for stability and weight reduction, and our footage of hummingbird foraging may provide valuable insight into the application of this feature for insectivorous foraging.