Strength of parrot flight feathers is a function of position on the wing.

Powered flight in birds is reliant on feathers forming an aerodynamic surface that resists air pressures. Many basic aspects of feather functionality are unknown, which hampers our understanding of wing function in birds. This study measured the dimensions of primary and secondary flight feathers of 19 species of parrots. The maximum force the feathers could withstand from below was also measured to mimic the pressures experienced during a downstroke. The analysis tested whether: (1) feather dimensions differed along the wing and among secondary and primary remiges; (2) the force that feathers could withstand varied among the remiges; and (3) there would be isometric relationships with body mass for feather characteristics. The results show that body mass significantly affected vane width, rachis thickness, maximum force, and ultimate bending moment, but the relationship for feather length only approached significance. Many of the proximal secondary feathers showed significantly lower values relative to the first primary, whereas for distal primaries the values were greater. There were isometric relationships for force measurements of primary and secondary feathers with body mass, but there was positive allometry for feather lengths and vane widths. The forces feathers can withstand vary along the wing may be a proxy for the aerodynamic properties of the feathers in situ. Broader taxonomic studies that explore these topics are required for other species representing a range of different orders. A better understanding of the functionality of feathers will improve our understanding of how avian flight works particularly considering the variety in flight style and wing shape in birds.