Influence of the trailing-edge notch on flight performance of galliforms

Abstract

Trailing-edge notches, formed by shortened first secondaries, characterize the wings of most galliforms. I investigated the function of these notches with comparative measurements of notch size taken from extended-wing specimens and with experimental studies of model wings of four representative species. Pheasants, quail, and turkeys, all of which use flight to escape predators, have wide wings and deep notches. Grouse with dark flight muscles have long, narrow wings with small trailing-edge notches and typically fly relatively long distances from one foraging site to another. Grouse with light colored flight muscles have short, broad wings with large trailing-edge notches and mostly fly from ground to canopy or from branch to branch to reach their food. Model wings of two pairs of galliforms with different wing shapes were used in the experiments. White-tailed Ptarmigan (Lagopus leucurus) and Sage Grouse (Centrocercus urophasianus) have small notches, high aspect ratios, relatively heavy wing loadings, low maximum lift coefficients, and dark pectoral muscles. In contrast, Wild Turkey (Meleagris gallopavo) and California Quail (Callipepla californica) have deep notches, low aspect ratios, relatively light wing loadings, high lift coefficients, and light colored pectoral muscles. Experiments using model wings in a water flow tunnel show that the trailing-edge notch increases the maximum lift-to-drag ratio and stabilizes airflow around the wing, but reduces the maximum, lift coefficient. Thus, the trailing-edge notch increases performance in vertical and slow flight but reduces efficiency in level flight. Such a function is consistent with the suite of differences these birds show in muscle color, wing shape, and predominant mode of flight.