Cover: A male volcano hummingbird (Selasphorusflammulatorridus). Males of this species perform a courtship dive for females in which they produce a buzzing sound with their notched inner tail-feathers. Clark and colleagues (pp. 3395−3403) demonstrate that tail-feathers from this species and several relatives produce sound by aeroelastic flutter. Aeroelastic flutter is a dynamic oscillation caused by feedback between the feathers’ structural properties and aerodynamic forces. Moreover, Clark et al. demonstrate that the mode of flutter matches one of the resonance frequencies of the feathers. Photo credit: Anand Varma (www.varmaphoto.com).